UDK 621.3:(53+54+621 +66)(05)(497.1 )=00 ISSN 0352-9045 22001 INFORMACIJE MIDEM, LETNIK 31, ST. 2(98), LJUBLJANA, junij 2001 UDK 621,3:(53+54+621 +66)(05)(497.1 )=00 ISSN 0352-9045 INFORMACIJE MIDEM 2 o 2001 INFORMACIJE MIDEM LETNIK 31, ŠT. 2(98), LJUBLJANA, JUNIJ 2001 INFORMACIJE MIDEM VOLUME 31, NO. 2(98), LJUBLJANA, JUNE 2001 Revija izhaja trimesečno (marec, junij, september, december). Izdaja strokovno društvo za mikroelektroniko, elektronske sestavne dele in materiale - MIDEM. Published quarterly (march, june, september, december) by Society for Microelectronics, Electronic Components and Materials • MIDEM. Glavni in odgovorni urednik Editor in Chief Dr. IztokŠorli, dipl.ing., MIKROIKS d.o.o., Ljubljana Tehnični urednik Executive Editor Uredniški odbor Editorial Board Časopisni svet International Advisory Board Naslov uredništva Headquarters Dr. Iztok Šorli, dipl.ing., MIKROIKS d.o.o., Ljubljana Doc. dr. Rudi Babič, dipl.ing., Fakulteta za elektrotehniko, računalništvo in informatiko Maribor Dr.Rudi Ročak, dipl.ing., MIKROIKS d.o.o., Ljubljana mag.Milan Slokan, dipl.ing., MIDEM, Ljubljana Zlatko Bele, dipl.ing., MIKROIKS d.o.o., Ljubljana Dr. Wolfgang Pribyl, Austria Mikro Systeme International AG, Unterpremstaetten mag. Meta Limpel, dipl.ing., MIDEM, Ljubljana Miloš Kogovšek, dipl.ing., Ljubljana Prof. Dr. Marija Kosec, dipl. ing., Inštitut Jožef Stefan, Ljubljana Prof. dr. Slavko Amon, dipl.ing., Fakulteta za elektrotehniko, Ljubljana, PREDSEDNIK - PRESIDENT Prof. dr. CorClaeys, IMEC, Leuven Dr. Jean-Marie Haussonne, EIC-LUSAC, Octeville Dr. Marko Hrovat, dipl.ing., Inštitut Jožef Stefan, Ljubljana Prof. dr. Zvonko Fazarinc, dipl.ing., CIS, Stanford University, Stanford t Prof. dr. Drago Kolar, dipl.ing., Inštitut Jožef Stefan, Ljubljana Dr. Giorgio Randone, ITALTEL S.I.T. spa, Milano Prof. dr. 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Grafična priprava in tisk BIRO M, Ljubljana Printed by Naklada 1000 izvodov Circulation 1000 issues Poštnina plačana pri pošti 1102 Ljubljana Slovenia Taxe Perçue UDK621.3:(53+54+621 +66), ISSN0352-9045 Informacije MIDEM 31(2001)2, Ljubljana ZNANSTVENO STROKOVNI PRISPEVKI PROFESSIONAL SCIENTIFIC PAPERS VV.Marks, S.Ritz: Integrirano vezje za PWM regulacijo DC motorja z odlično EMC skladnostjo 69 W.Marks, S.Ritz: PWM DC Motor Regulator IC with Excellent EMC Behaviour Ž.Čučej, P.Cafuta, R.Svečko: Tokovna regulacija skupka napetostno izvorni pretvornik - izmenični motor brez uporabe modulatorja 74 Ž.Čučej, P.Cafuta, R.Svečko: PWM-less Current Control at VSI-IM Drive F.Novak: Upoštevanje zmožnosti testiranja pri načrtovanju sistema-v-čipu 84 F.Novak: Testability Issues of System-on-chip Design T.Dogša: Dodatni primerjalni testi za simulatorje SPICE 88 T.Dogša: Additional Benchmark Tests for SPICE Simulators Ž.Čučej: Gradniki močnostne elektronike: pregled 94 Ž.Čučej: Power Electronics Building Blocks: a Survey R.Osredkar, B.Gspan: Študija omejitev planarizacijske tehnike s tanko plastjo tekočega stekla, (SOG) 102 R.Osredkar, B.Gspan: A Study of the Limits of Spin-on-glass Planarization Process M.Bunc, J.Rozman: Elektronska opornica za pasivno gibanje pasje noge in meritev kontrakcije v pasjem kolenskem sklepu 106 M.Bunc, J.Rozman: Electronic Brace for the Measurements and Eliciting of Muscle Contractions in a Dog's Ankle APLIKACIJSKI ČLANKI APPLICATION ARTICLES I.Šorli: Zamenjava tantalovih kondenzatorjev s keramičnimi 110 I.Šorli: Tantalum Capacitor Replacement with Ceramic Capacitor POROČILA S KONFERENCE CONFERENCE REPORTS M.Hrovat: Konferenca Micro Tech 2001, London 115 M.Hrovat: Conference Micro Tech 2001, London PRIKAZ MAGISTRSKIH DEL IN DOKTORATOV - LETO 2000 119 MS and PhD ABSTRACTS - YEAR 2000 MIDEM prijavnica 133 MIDEM Registration Form Slika na naslovnici: Družina mikrokontrolerjev firme STM - pot do uspeha Front page: STM MCU ST Family - Road to success VSEBINA CONTENT 37th INTERNATIONAL CONFERENCE ON MICROELECTRONICS, DEVICES AND MATERIALS and the WORKSHOP on OPTOELECTRONIC DEVICES AND APPLICATIONS October 10. - 12. 2001 Bohinj, SLOVENIA PRELIMINARY PROGRAMME http://paris.fe.uni-lj.si/midem/conf2001/ Elektrotehniška Zveza Slovenije Slovenia Section IEEE UDK621,3:(53+54+621 +66), ISSN0352-9045 Informacije MIDEM 31 (2001 )2, Ljubljana PWM DC MOTOR REGULATOR IC WITH EXCELLENT EMC BEHAVIOR W.Marks, S.Ritz AMS, Austria Mikro Systeme International AG, Graz, Austria Key words: electric motors, DC motors, Direct Current motors, motor control, motor regulation, PWM regulators, Pulse Width Modulated regulators, AS8410 IC Integrated Circuits, EMC, ElectroMagnetic Compatibility, single chip solutions, high voltage technologies Abstract: This is an introduction to the AS8410 control IC and associated device modules for PWM DC motor control. This IC enables equipment manufacturers to combine two features of electronically controlled DC motors, which were previously considered incompatible: High power efficiency (>95 %) and minimal electromagnetic radiation, to include the high frequency range (RF emission significantly below VDE0871, VDE0875, VDE0879 standards) with high PWM frequencies. Extensive load failure diagnosis and error processing routine, as well as easily programmable operating modes, provide secure and low-cost application over a spectrum of DC motor control application. Integrirano vezje za PWM regulacijo DC motorja z izvrstno EMC skladnostjo Ključne besede: motorji električni, DC motorji na tok enosmerni, krmiljenje motorjev, regulacija motorjev, PWM regulatorji modulirani impulzno širinsko, AS8410 IC vezja integrirana, EMC kompatibilnost elektromagnetna, izvedbe na enem chip-u, tehnologije visokonapetostne Izvleček: V prispevku je predstavljeno Integrirano vezje AS8410 proizvajalca AMS za PWM regulacijo DC motorja. To integrirano vezje omogoča uporabnikom kombinacijo dveh lastnosti, ki sta pri elektronsko krmiljenih motorjih do sedaj bili nekompatibilni: visok izkoristek moči (>95%) in minimalno elektromagnetno sevanje zlasti na področju visokih frekvenc (RF sevanje občutno pod standardi VDE0871, VDE0875 in VDE0879 ). Možnost nadzora in analize odpovedi bremena, rutina za obdelavo napak, lahko programljivi načini dela omogočajo varno in ceneno uporabo tega integriranega vezja v široki paleti regulacijskih elektronik za krmiljenje DC motorjev. Motivation The principle of DC motor speed or power/torque control and regulation through a pulse-width modulated electronic switch is not new. Such switch operation produced the desired motor speed-torque control, but caused electromagnetic emission of significant amplitudes in a wide, mainly high frequency range, making an obstacle to its wide application. It also prevented application in EMC-sensitive environments (e.g. automotive applications near other interference-sensitive electronic systems like car radio, air-bag, etc.) or required additional, economically questionable shielding procedures. In such cases, exclusive analog motor control has been used, which holds the great disadvantage of poor power efficiency (high dissipation in the power regulating transistor). The tremendous demand for energy-saving, convenient, environment-friendly (low-noise, EMC-conform) and cost-effective devices for electric motors with variable (controlled) speed and/or speed-torque has resulted in world-wide R&D activities of considerable expenditure. These developments match the increasing use of brush-less, electronically commutated motors. To reach a broad, low-cost electronic control systems are absolutely necessary for these motors. We developed our standard product AS8410 and the associated modules for DC motor regulators (voltage regulators) with PWM control. On one hand, this allows the advantage of pulse control without the disadvantage of high interference emission, and on the other hand, provides a low-cost device for a broad application spectrum (for motors power-rated from a few watts to several kilowatts in different operating modes with comprehensive load diagnosis and error processing mechanisms). The AS8410 realization was also designed to generally enable PWM control of inductive loads and/or inductance-affected loads (e.g. switch regulators) with very good EMC behavior. Since automotive field application was planned from the very beginning, all requirements for 12V or 24V direct system operation had to be met (load dump, burst and surge impulses on the battery supply, EMC susceptibility, minimal RF emission, broad supply voltage range, low current consumption, automatic sleep mode, etc.) System solution and EMC- conform operation The AS8410 is made with analog/digital CMOS (BiCMOS) high-voltage technology (2) and delivered in a standard SOIC16 package. The system concept realizes an ana- 69 Informacije MIDEM 31 (2001 )2, str. 69-73 W.Marks, S.Ritz: PWM DC Motor Regulator IC with Excellent EMC Behavior log/digital (mixed signal) IC with primary analog functions. It contains a complete load regulator loop. Additionally, comprehensive load diagnosis and failure processing procedures, temperature and supply voltage monitoring and protection are integrated. The AS8410 operates in a supply voltage range of Vmin = 6V to Vmax = 34 V (or 44V) enabling direct application to 12V or 24V automotive power supply. Operating temperature range:-40 °C to +125 °C. The remarkable feature for achieving this good EMC behavior is the power (switch) transistor drive method. The power FET driver unit consists of fast current and voltage controlled current sources, and the control of these current sources through the instantaneous value of the onload (motor) voltage (slew rate regulation). Finally, the motor performance rating (rated load current) is selected through the current control of these current sources (externally programmable), and the voltage control realizes the EMC-conform operation. With this application, the gate of an external power FET and the motor voltage time variation during the PWM motor voltage rise and drop is controlled by the motor voltage instantaneous value. In this way, the electromagnetic emissions of the entire control module are minimized and almost totally dissipate in the high-frequency range (Fig. 1). The exceptionally low emission levels, particularly in the high-frequency range, are clearly seen in Fig.1. The motor regulator application does not require any filter devices. The AS8410 system concept The AS8410 forms a complete PWM DC motor regulator loop and consists of the following sub-blocks: Set value input signal processing, generating the characteristic curve of the regulator (see Fig. 2), feedback value measurement (load detection at the high side of the motor), and a PWM generator (controlled by the set value and the actual motor current value) as well as the power FET gate driver. The control of the external power FET is effected by the special current controlled feedback sources described above. The control voltage is generated by an internal charge pump and is 10 V higher than the system power supply. The AS8410 requires only one supply voltage, which usually is the same as the motor supply, and ranges from 6V to 34V (Vmax = 40V). Regarding the security concept, load failure detection circuits (over current, motor blocking, no load of the motor, or open wire, commutator and power FET short circuits) as well as over temperature and over or under voltage detection, are integrated. Additionally, a special circuit protects the power FET in generator mode of the motor (coast-down of motor due to mechanical inertia). Sequence control is performed by a logic block, detecting systems status (failures, operating modes) and translating them into internal control signals and an external failure feedback signal (operating modus 1). See Fig. 2 for AS8410 system schematic. a 4 s i ,' 5 ;; 2 :i * * is ? ¡? .2 is ; 4 ?; s « a ' ¡4 Fig. 1 Emission spectrum comparison - AS8410 controlled motor regulator versus a commercially available solution, showing much lower RF emission using a 10A rated motor current. 70 W.Marks, S.Ritz: PWM DC Motor Regulator IC with Excellent EMC Behavior Informacije MIDEM 31 (2001 )2, str. 69-73 Fig. 2 Block diagram - AS8410 PWM DC Motor Regulator Circuit Security concept Another significant aspect in the system design of AS8410 was comprehensive failure diagnosis in the load circuitry (DC motor and power switch) and AS8410 self-controlled failure processing procedures (relieving the IC-controlling MP or IC application in systems without MPs). The AS8410 detects and treats various failure states of the power load circuit, returns a failure report signal to the set value pin, and performs an analog/digital failure processing procedure according to the type of failure. Load circuit monitoring is performed by analog motor current measurement at the high side of the motor, and motor voltage mean measurement. The following specified failures are diagnosed by the AS8410 in operating mode 1, and processed with analog/ digital procedures by the IC itself: 1. Over current or short circuit of the motor. 2. No load of the motor (e.g. torn belt) or open wire. 3. Short-circuited power switch (power FET). 4. Mechanically blocked motor, 5. Short-circuited commutator (carbon brush clogging). 6. Protective function for the power FET and the AS8410 itself, when motor is in generator mode (during coast-down due to mechanical inertia). 7. Over or under voltage (supply voltage). 8. Over temperature. Fig. 4 gives an example of some sequences of AS8410 internal events during an analog/digital failure processing procedure. TeK Stop: 250 S.'s ? Acqs Fig. 4 Example of an AS8410 motor failure processing procedure. 71 Informacije MIDEM 31 (2001 )2, str. 69-73 W.Marks, S.Ritz: PWM DC Motor Regulator IC with Excellent EMC Behavior The wide application range and main application properties An additional aspect in the development of theAS8410 was its wide application scope. The following functional and parametric properties can be customized by simple programming with external devices: 1. Adapting to different DC motor power ratings is effected by programming the control currents at two analog pins. With this, control currents to the gate of the power FET-switch up to 300 mA can be delivered on chip, so that even high-performance FET's (or parallel power FET's for rated load currents in the >100A range) with effective gate source capacities of 10nF switching time down to 150 ns are possible (slew rate > 100 V/ms). Even with these short switching times, good EMC behavior is achieved by the edge-control-led drive. The short switching times allow relatively high PWM frequencies (presently 20kHz are realized) with a power efficiency of > 95 %. At the other end of the motor performance ratings, motors with rated currents in the mA range can be driven with the same properties. 2. The programming of different functional properties is realized by two additional pins (a digital pin and an analog pin): 2.1. Set value input mode and temperature monitoring are set with the digital pin as follows: a) Operating mode 1: The set value (motor cur-rent or speed) is given as duty ratio of a low frequency PWM signal. The frequency of this signal is optional within a wide range (e.g. 10Hz, like the PWM output signal of many microprocessors). b) Operating mode 2: The set value is given as analog voltage in the range 0 - 5V at the same set value input pin. c) Temperature monitoring by an excess-temper-ature threshold, which is externally and analog programmable, with two different control modes in the case of over temperature: Operating mode 1 brings the motor current (motor speed) to 100 % of the rated value, if the temperature threshold is exceeded. This protects a system where dissipation is not produced by the controlled DC motor (e.g. overheated combustion engine fan-cooled by the DC motor). Operating mode 2 regulates the load circuitry for the system temperature not to exceed the threshold value (comparable to a thermostat). This protects a system where dissipation is produced by the controlled DC motor (or the switching transistor itself). In this case the motor output is brought down - independent from the set value - to a predefined temperature threshold value (this might even lead to a total DC motor shut-down). A special control was planned for cooling an overheated combustion engine (heat accumulation in a parked automobile): The DC motor regulator control is switched over from mode 1 to mode 2 with the ignition key. If the engine was overheated, the DC motor (cooling fan) starts operating in mode 2 after shut off with 100% PWM repetition rate, until the permissible temperature is reached. 2.2. Within a wide option range, the regulator time constant can be set by the analog pin using a capacitor. A time constant in the seconds range, for example, enables soft regulating behavior, i.e. relatively slow motor speed increase or decrease toward the programmed set value. 3. In operating mode 2 the ASIC is automatically put in power-down mode through set values of < 4 % of the rated current (nominal speed). Current drawing is ap-prox. 300 mA. Despite its extensive programmability, the AS8410 has only 16 pins and is delivered in a standard SOIC16 package. This standard product is a successful, cost-effective bulk product. The application circuitry in operating mode 1 and 2 is shown in Fig. 3. Fig. 3 Application circuits of the DC Motor regulator in operating mode 1 (left) and operating mode 2 (right) 72 W.Marks, S.Ritz: PWM DC Motor Regulator IC with Excellent EMC Behavior Informacije MIDEM 31 (2001 )2, str. 69-73 The most remarkable property of DC motor regulator modules associated with the presented AS8410 is certainly the nearly RF emission-free (EMC complying) operation combined with high efficiency (>95 %) and relatively high PWM frequency (approx. 20kHz, which is beyond the audible range). This enables compliance with EMC regulations and application of PWM controlled DC motor regulators in electromagnetic sensitive environments (e.g. automotive field). The low radiation susceptibility (> 300 mV) and the reliability of the control modules proved successful in their multiple automotive industry application. The simple programmability for various rated DC motors, the entire security concept, and the operating modes have opened large application fields to the AS8410. face and, on the other hand, control/regulator ICs that provide a single chip solution to the mass market of controlled DC motors. Literature /1/ Maurice, Bruno: Mit dem richtigen Dreh in Schwung kommen. Elektronik 24/1996, Pages 76 - 87 /2/ Austria Mlkro Systeme International AG, CMOS-Hochvolt-Tech-nologien /3/ Kupris, Gerald: Mehr als eine Vernuftehe. Elektronik 24/2000, Pages 62 - 68 /4/ Murarl, Bruno: Verknüpfung von Leistung und Intelligenz. Elektronik 15/1996, Pages 30-36 A glimpse of the future The AS8410 in PWM DC motor regulators can now already be applied, whereverthe described properties result in significant, cost-effective inherent utility increase, and favorable EMC behavior of DC motor-operated equipment (e.g. do-it-yourself machines, household appliances, automotive applications, variable speed and actuating drive units in automation systems, etc.). With this PWM control, DC-DC converters can also be applied (good EMC behavior). Advance developments on the basis of the AS8410 deal with the system concept (e.g. brushless motor control, effective speed control, etc.), single system components, and motor control/regulator ICs with convenient pP inter- W.Marks, S.Ritz AMS, Austria Mikro Systeme International AG Schloss Premstaetten A-1841 Unterpremstaetten, AUSTRIA Tel.+43 3136 500 5449, fax.+43 3136 500 5420 Further information can also be found on Internet web-page: www.amsint.com Prispelo (Arrived): 03.04.2001 Sprejeto (Accepted): 01.06.2001 73 Informacije MIDEM 31 (2001 )2, Ljubljana UDK621,3:(53+54+621 +66), ISSN0352-9045 PWM LESS CURRENT CONTROL AT VSMM DRIVE Žarko Čučej, Peter Cafuta, and Rajko Svečko University of Maribor, Slovenia Keywords: electric motors, IM, Induction Motors, FOC, Field Oriented Control, current control, PWM Inverters, Pulse Width Modulated inverters, VSI, Voltage Source Inverters, VSC, Variable Structure Control, BLSC, Boundary Layer Switching Controllers, SCC, Switching Current Control, time-discrete switching variable structure control, optimized mappings Abstract: This paper discusses time-discrete field oriented variable structure current control of induction motor - voltage source inverter system without use of a pulse-width modulator. The controller is supplemented by feedforward selection of optimized mapping of controllers into voltage source inverter states. This proposed approach of direct inverter control depends on the boundary layer control, and the sign, nominal value and maximal values of the back e.m.f. estimate. It lessens back e.m.f. influence on chattering and makes It possible to extend the field angular velocity range of constant rotor field. Boundary layer control separates variable structure control modes. Supporting preassigned switching order and control objectives is assigned to each attraction domain. Tokovna regulacija skupka napetostno izvorni pretvornik -izmenični motor brez uporabe modulatorja Ključne besede: motorji električni, IM motorji indukcijski, FOC krmiljenje v orientaciji polja, krmiljenje tokovno, PWM Inverterji modulirani impulzno širinsko, VSI inverterji napetostno izvorni, VSC krmiljenje s strukturo spremenljivo, BLSC, krmilniki komutacijski plasti mejnih, SCC krmiljenje toka komuti-rajočega, krmiljenje s strukturo spremenljivo časovno-diskretno, preslikave optimirane Povzetek: Članek obravnava časovno diskretno tokovno regulacijo s spremenljivo strukturo v poljskih koordinatah skupka asinhronski motor - napetostno izvorni pretvornik brez uporabe modulatorja. Regulatorje izpopolnjen s predkrmiljenjem izbiranja optimalne preslikave stanj v stanja pretvornika. Ta predlog direktnega krmiljenja pretvornikov je odvisna od režima regulacije in predznaka, minimalne ter maksimalne inducirane napetosti v motorju. Z njo se v veliki meri kompenzira vpliv inducirane napetosti motorja na drhtenje. V primerjavi z običajnimi rešitvami omogoči tudi razširitev vrtne hitrosti pri konstantnem rotorskem polju. Pasovni regulator razmeji režime regulacije s spremenljivo strukturo. Vsakemu režimu predpiše atrakcijsko domeno, ki omogoča predpisano zaporedje preklapljanja in kriterije kvalitete regulacije. 1 Introduction For an Induction Motor (IM) the Pulse-Width Modulation (PWM) of the Voltage Source Inverter (VSI) plays an important role in the control system, since not only the level but also the phase of input signal must be controlled. These occur as certain disadvantages of PWM inverters because they are determined by the characteristics of PWM and are not addressable by controllers /1 / . These drawbacks can be eliminated by switching the variable structure (which has a direct control VSI - IM system) constructed by signals as the position, velocity, and currents, which contain information about disturbances and parameter variation, consequently the entire control system is completely accessible to control and can be optimized in a Variable Structure Control (VSC) design. Unfortunately, time-discrete implementation of switching type VSC causes chattering, degrading all the benefits of direct switching control. In /2/,/3/ we describe chattering reduction using hysteresis controllers and in /4/ using finite automaton. The recent article /5/ proposes quasi VSC implemented with a first order deadbeat controller and a space-vector PWM. Regardless of the fact that the ob- tained average current error is smaller than at direct switching control, this solution has some serious limitations. Disturbances should be smooth and limited, control robustness depends on the disturbance estimator used, and PWM properties are uncontrollable. In this paper we present the Boundary Layer Switching Controller (BLSC) used in Field Oriented Control (FOC) adapted with a feedforward steering selection for mapping of the controllers states into VSI states. Using BLSC the fixed order switching is determined, and to each of its phases mapping is optimized in regard to the following control objectives: sliding mode reaching time, average current error offset, chattering, VSI switching losses. Mapping optimization compared to /6/ involves zero voltage vectors. This introduced feedforward selection is similar to predictive current control /7/, except that: (i) the control is still VSC, and (ii) instead of back e.m.f., only information about the field velocity sign, and minimal and maximal values of back e.m.f. estimates are used. This work was supported in part by the Slovene Research Ministry under Grant J2-1644-0796-99. 74 Ž. Čučej, P. Cafuta, R. Svečko: PWM less current control at VSI-IM drive Informacije MIDEM 31(2001)2, str.74-83 This article is organized as follows. Problem presentation with description of VSI, IM model and a summary of VSC is contained in section 2. In section 3 the proposed control with compensation of back e.m.f., feedforward steering and design of ST is given. Results of simulations are collected in section 4. This article ends with conclusions and appendices containing derivation of zero dynamics, IM model and analysis of stability for use of zero voltages. 2. Problem presentation IM is feed by a 3-leg bridge VSI supplied by DC voltage E and direct controlled by current switching controllers In the inner loop of FOC. VSI has eight states, which determine six active voltage vectors uk,k = 1,... 6 with constant amplitude uk =2E/3 and two zero voltage vectorsuk e {k0,«7} (Fig. 1). 2.1 FOC We assumed that FOC has a multi-loop structure and Is sampled every Ts seconds, i.e. algorithms are implementa-ble in the digital signal processor. Outer loops contain state controllers and estimators for the load torque T, , rotor magnetization current imR , and angle $. They are responsible for the tracking of drive kinematics variables and the regulation of imR . Field weakening is not considered. The selection of design coefficients c,, c,, and c3 (elaborated in Appendix A and Appendix B) of outer control loops should guarantee stable zero dynamics with a stationary point: ft = 0 = i//R = o and 0 = cp = ijrR = 0. Outputs from outer loops and current control loops. serve as command values for inner ; H, = ! =0 H(l,l,0) ; -En 1 i u{ =u(svs2,s3) \ =«(1,0,0) ; w g -b W/J i C «JiSAto -m — ' slak» v'O « ; 0.(1.01 «7 —tt(l,l,l) -> d «(0,1,1) SoAi) H(1'°'1) Fig. 1: Voltage vector representation from the d-q frame perspective, inverter, and load circuit. A symmetrical, 3-phase IM with Y stator windings with a galvanic isolated central tap is considered. Its voltage model in d-q frame is described by the following MIMO system: w0 = Ris + Lsapis0 + e0 , 0 e {d, q}, (1) where u = (d qj is stator voltage vector, Rs and Ls0 are rotor resistance and rotor leakage inductance respectively, is sum of back e.m.f. and crosscoupled voltages (e,i = e„q + e,n > e„ = e<„, + e„i), and pi = di/dt ■ Latter, In the design we use a simple modified model: LsaPho ~ 11 kO eo which is derived in Appendix C. (2) 2.2 Current variable structure control The control problem being considered Is a determination of sequence and the duration of VSI states, so that by tracking and the drive FOC is satisfied: s = |V J ■iREF - i (3) i.e. VSC is established in stator currents error space []2 where s0 - 0, Oed,q are switching subspaces. This formulation embraces the control of stator currents and modulation of VSI outputs as one problem, which is solved by a MIMO VSC. It is well known /9/, /10/, that the design of VSC can be done by satisfying a reaching condition. In FOC the torque and magnetization control are decoupled, meaning that the MIMO current control is designed by two independent controllers, which fulfill reaching conditions written in compact form as: Sr sdsd < 0 5ß : šgSq < 0 S0: SD H SQ by discontinuous control: (4a) (4b) (4c) vA K if |X if < o (5) with discontinuity on the switching subspaces S,. The set of control vectors v = [v(/ v,Je v., _/ = !,... 4 is present- 75 Informacije MIDEM 31(2001)2, str. 74-83 Ž. Čučej, P. Cafuta, R. Svečko: PWM less current control ai VSI-IM drive ed in Fig. 2a. Control (5) ensuring (in ideal circumstances, when switching frequency is infinite) or sliding on SD with reaching to S0, or sliding on SQ with reaching to SD either sliding on S0. Only in the last case is the request (1) completely satisfied. The PWM's less mapping between control vector v and stator voltage vector u gives IM stator voltage equation (2). Combining (4a), (4b) and (1) gives: H A |«il = 2£73=l , ' ! u 0,96 -...........-7„; / *>\/*< \ \60° v.. : V;-V'- ,„ ud -0,96 Fig 2: Presentation of control vectors (a) and mapping range (b). L, -(Uk0~e0) 'Sa S« < 0 -> s0 < 0 , uk() > j0 > 0 , uk0 < e, (6) and can be simply implemented using digital signal processors. ST performs mapping where selection of columns addressed by p quantizer performs an inverse transformation from d-q to abc space. Time discrete implementation of the decoupled SCC causes inverter outputs to have a finite pulse such as pulse width modulation. Their duration is equal to one sample interval and occasionally to an integer multiple of Ts. Therefore the decoupled SCC is never in SM. Consequently difference in control vector amplitudes, i.e. |vr e. cause offset in | e | and subharmonic oscillation (in regard to frequency 1/TS) of local average of |e | (determined by stator time constant) causing torque chattering. If VSC, for control robustness is designed at max|e0|, for mapping v —» u from (6) it follows: uko(P) when uk0 < - max e0 when uk0 > maxleJ (7) Due to the rotation of the active voltage vectors and their angular displacement at 60°, the mapping links control vectors {v;} with four angular sectors in d-q frame containing voltage vectors } involved in mapping. The sectors placements depend on terms e0 (or cl(), see (31) in Appendix C), but in the case of (7) only on their maximal amplitude. Therefore angle sectors are placed symmetrically as are the symmetrical control vectors v. (Fig. 2b). 2.3 Implementation of decoupled switching current control This described current control is named decoupled Switching Current Control (SCC). It is of simple structure (Fig. 3) Fig. 3: Realization of decoupled SCC. The other important drawbacks of mapping (7) are: (i) zero vector voltages are uninvolved, and (ii) for components of the selected voltage vector the following holds max jud I = max |uq | and min |ud | = min\u\ (8) which limits the velocity range of nominal magnetization to: max e0 <0,25(25/3) (9) Absence of zero voltages cause high total switching frequency of VSI (at least twice that of 1/TS), consequently VSI switching losses are very high. 3 Proposed switching current control Decoupled SCC performances are well enhanced with Fixed-order sliding mode switching scheme /10/, where the sliding mode takes its place in a preassigned order while state is traversing the state space: 76 Ž. Čučej, P. Cafuta, R. Svečko: PWM less current control at VSI-IM drive Informacije MIDEM 31 (2001 )2, str.74-83 moving along SD only in initialization phase during the establishment of nominal rotor magnetization; in regular control it mode moves in order Sn ^ iS"n (10) and then maintaining limit cycle around S0. Mappings supporting (10), should adopt attraction to VSC modes. For SQ the minimal S0 reaching time is requested, after reaching S0 it is desirable to maintain the limit cycle around s-origin so, that the current ripple is redirected from torque into magnetization control (where it is well dumped by large rotor lag) and in VSI switching sequences the minimal number of switches is involved. This is achieved by deliberate use of zero voltage vectors in mapping. 3.1 Boundary Layer Switching Control The fixed-order sliding mode switching scheme is made possible by the Boundary Layer Switching Control (BLSC), which separates the associated VSC modes. According to above description it has to differentiate between three VSC modes: mode of moving along SQ mode of limit cycle at S0, which has two phases: phase of obeying (4b). phase of obeying (4c). These modes besides the mapping range presented in Fig. 2b, which accommodates attraction domain ADQ, need two further domains: domain A() belonging S0, where v~,v* are mapped into u with minimal amplitudes of ukq fulfilling (6), and vj, vj into u with maximal amplitudes of ukq, domain AQ belonging SQ where mapping requests are opposite to requests for domain \ . BLSC, which fulfills the above requirements, has three layers of coaxial arrangement with a center in s-plane origin (Fig. 4). -(¡A I domain A r :W2f: ^ domain ADq ■ i domain Ar % + b sq=0\ The borders between attraction domains are determined by the current error caused by maximal voltage amplitude, which arises in a stationary condition in one sampling interval. Using the estimation of sq with difference A^/T, for border between AQ and ADQ we can state: L, (11) 'Sa For inner border (between ADQ and we consider in (11) maximal allowed back e.m.f.. Because u max e„ - > 2 (12) it follows, that in q direction the inner border is b / 2 . Boundaries in d direction we settled to ±b . This choice is based on a consideration that in the limit cycle around the error plane origin (s = 0) a sequence of voltage vectors could be formed, where zero voltage vectors follow each active vector. In this case the border in d direction should be at least so far from the origin of s-plane that sd, i.e. current error in d direction can be zeroed by max | ud \. Thus borders in d direction should be calculated similarly to borders in q direction, i.e. by (11) with consideration for adequate voltages in d direction. Because and max \ ed |< max \ e \ we justify max u i - max 111 „ Fig. 4: Borders and discrete VSC modes. aforementioned choice of ±b for d direction. Note, the boundaries are tied to the sampling interval Ts, and their size actually determines the duration of sampling interval. In many IM control designs, the value of the sampling interval Ts is influenced more by desired rotor field angular accuracy, the rms value of stator current chattering, and invertervolume power density than by IM dynamic requests. One of this project's goals was to make the sampling interval as short as possible in regard to the limitations of the used digital signal processor. The target value was 25 jus. 3.2 Compensation of eq Use of zero voltage vectors u0 uy in mapping during limit cycle reduces offset and chatter of local average (in interval determined by the motor's time constants respectively), but for dump these phenomena, e0 should be compensated. Due to switching controllers they cannot be compensated by subtraction of e0 as is done for predictive controllers / 77 Informacije MIDEM 31 (2001 )2, str. 74-83 Ž. Čučej, P. Cafuta, R. Svečko: PWM less current control at VSI-IM drive /7/. Rather, the slowly-occurring magnetization offset (caused by ed) is minimized by rotor magnetization control (see Appendix B), and oscillation of local average of sq causing torque chattering, is effectively minimized by mapping with property (13) sin pXB>- mine u » smft8 mine, >-'L (16) Sector is placed in p]B < p< piB + f and similarly for sector hold p3B < p < p3B + f . When hold p < 0 , then we obtain: From (7) at eq > 0 follows vq = uq + eq and v+q = uq - eq where u',u* denotes voltages to which v" and v* are '■! '■/ ^ CI 0 and limit min (v* ) = max (eq), after a short calculation we obtain: sin As ^ mine >-1 u , sin p3B < mm e„ 'i u (17) The position of even sectors and $4 are symmetrically over q-axe to position of and respectively. Zero voltage vectors take place in A0 domain only and their selections is independent of field angle p . They are applied according to: min m = - min el (14) This suboptimal solution enables a simple construction of the angular sectors distributions. Moreover, exact calculation in the case of min(^) is by (7) limited to (14). Mapping, considering (13) and (14) and the preassigned switching order is then: I vd when sd > 0 vt when s,, < 0 (15a) if« [(n - 1)TS ] = m7 v u2 v u4 v u6 then u («Ts) = u1 (18) else u(nTs~)-u0 where nTs is the sampling instant. This selection gives minimal VSI over-switching at the voltage vectors change [2], As this is excellent for VSI and enables good compensation of eq, it should be noted that at zero vector voltage the IM is effectively allowed to coast. Control seems to be lost during this time, but stability is still preserved because besides conditions (33) and (10) the following condition ukq{p)~eq when u,, > - min el Kci [ H | when u,., < max\e. (15b) sign i = sign e (19) is also fulfilled (see stability analysis in Appendix D). when «,, < min e I kci i (i i when u, > - max \er (15c) where (15b) and (15c) are valid for positive and negative eq respectively. The position of angular sectors dj, containing vectors uk is determined by the geometric relationship between | uq \ and | u(p) | at pjB and pjK , where angles pjB and pJE denote the beginning and end of angular sector &j (Fig.5). At p>0 for odd sectors plB and piE can be generally written as: I/' . "sector // max|e;, "iq\ i) i/ I iq I v min|i> | = 0 I ' X \ i .JS*^ _____y&zL. ► - - 'f\\ ^ /¡\ x ...X....T.... is i£° j/ > 78 Ž. Čučej, P. Cafuta, R. Svečko: PWM less current control at VSI-IM drive Informacije MIDEM 31 (2001 )2, str.74-83 sector i3i: 02£ <1 W "o- / «i cB Hq J 2 e Jh / \ max\ek <4 d min| eiq | = 0 sector -64:/ Fig. 5: Determination of pjB and pjE in nominal field angular velocity range. 3,3 Implementation of proposed current control The structure of the proposed current switching control is shown in Fig. 6. BLSC is implemented by a 2-dimensional 4-level quantizer separating the attractors domains A0, ADQ and Aq . Switching table ST is result of logic superposition of angular sectors determined in subsections 3.1 and 3.2 respectively. Feedforwarded p is quantized by a four-lev-el quantizer. It determines max and min value of back e.m.f. (because eq = eiq + edq, whereas constant field is proportional to p and edq varies according to p and fast iSd, it is simple to evaluate max9 and mmeq for positive and negative angular velocity range of p). In the case, where distinguishing between ADQ and Ag domains is less important than maximal p with constant rotor field, the voltage range for AQ can be exploited in ADQ domain. This in comparison to decoupled SCC enables to doubling of the p range of the constant rotor field, Table 1. JfcL 5 W- BLSC abc W: feedforward steering .....N —1/ '42 <5 V VSI p quantizer (onJ5° sectors) p A uk = u(a,b,c) is(d,q) \abc dq\ is(a,b,c) Fig. 6: Proposed control with mapping and feedforward steering. Table 1: Pairs max e? - mmeq in nominal and extended velocity ranges. pscc is maximal p range of SCC. velocity range max e p> 0 0,25(2E/3) 0 0 >p> -pscc 0 - 0,25(25/3) 2 Pscc ^P^ Pscc 0,5(203) 0,25(203) -Pscc ^P^ -2Pscc -0,25(203) - 0,5(2£73) ST consists of 9 subtables, see Table 2. They are addressed by attractors domains A: and angular velocity range p.. The rows in the subtable are determined by the signum functions of BLSC. Columns are addressed by p quantizer determining 24 angular quants 6C. The inverse transformation from d-q to abc frame is the domain of columns. Determination of zero voltage vectors according to (18) follows ST. 79 Informacije MIDEM 31(2001)2, str. 74-83 Ž. Čučej, P. Cafuta, R. Svečko: PWM less current control ai VSI-IM drive Table 2: Switching table (ST). The VSI switches states are denoted by the corresponding voltage vectors. 0,: 0>p>-^ V d2L 6, Ö3 % dn subtable #1: AD0 ; pscc > p > -pscc li- M, u, M, "fi "fi "fi "fi M| V, li, "fi M, M, M, M, M7 H, v. u? i/, "3 «4 «4 V4 U3 "4 "4 "4 "4 "5 "5 «5 "5 subtable #2: A0 ; pscc > p > 0 u, »4 «4 «4 "4 M, us us "5 "fi V2 "fi i/. "l M, ii. u7 II, 11, H, U3 U, U, u3 «4 «4 u4 V4 u, Ziç "3 "4 "4 «4 "4 "5 "s «5 subtable #3: A0 ; 0 > p > ~pscc u, H, "fi "fi "fi "fi ii. ï/j M, V2 "fi "fi "fi M, M, a. u7 u0 ii. II-, M, i/, u, «4 II, «4 "4 "4 "4 "5 "5 "5 "6 subtable #4: Aq ; pscc > p > 0 us "s "fi "fi "fi "fi M, M, i/. v, u6 "fi "fi i/. M, U, V3,v4 zero voltage vectors, determined by (18) subtable #5: Aq ; 0 > p > Oscc V,, v2 zero voltage vectors, determined by (18) v3 u, M? M3 U3 «4 V4 U3 «4 "4 «4 «4 "5 M, M, "5 "fi subtable #6: AD0 ,A0\ p> pscc "l "4 "4 "4 «4 "s M, M, "fi "a Mfi "l Ž/, H, ii, ll? M, M, U, "4 "4 "4 11, M3 i/3 "4 "4 "4 "4 «5 M, M, subtable #7: AD0 , A0 ; -pscc > p M, "5 "fi "fi "fi "fi i/, 11, v, "fi "fi "fi M, M, ÏÎ. M| i/, M, U? V3 M, M, M? "3 "3 "4 "3 «4 "4 «4 M5 u5 "5 "5 "fi subtable #8: \ ; p > Pscc U, "4 "4 «4 M4 M, Us K, us "fi V, "fi M, ii. M, W? ll1 M? U? U, ... zero voltage vectors, determined by (18) subtable #9: Aq ; ~pscc > p V, . V, zero voltage vectors, determined by (18) H? "9 Uj w3 M3 u4 ^4 «3 «4 «4 "4 "4 "5 "5 "5 "fi 80 4. Simulation A property of the proposed control with feedforward steering of optimized mappings has been evaluated by simulation. Data for IM, VSI, controllers, and perturbed tracking task considered in simulations are collected In Table 3. Table 3: Motor, inverter, controllers, and task data. Motor: four pole, 1480 rpm, Y connected stator windings with isolated central tap Parameters: Rs = 0,65 Q Ls= 1,65 mH Te =4Nm TP= 0,12 s 7 =0,000656 kgm2 Inverter: 3-phase bridge, supply voltage £ = 310 Control: SCC proposed BLSC border: b - 3 A . ¡iff magnetization reference 4,75 A 4,75 A Kinematics: c, =70000, c1 = 1000 , c, =100 Perturbed tracking task: 4.7 I [rail]--' position (p max ~ angular velocity ij' T,. J -lL_T ,.,.,.,.-., ..t 10 20 30 40 50 [ms] The chosen task enables testing of the proposed mapping in all VSC modes. Simulation starts by initialization, where the nominal rotor magnetic field is established, then AQ and Adq follow, which are disturbed in 15th milliseconds with a change of the load torque. It pushes VSC into RM. The perturbation of the inertia J is used for evaluation of the robustness against IM parameter variation. To show the properties of the proposed mapping, a comparison to SCC (characterized by Fig. 2b and presented in Fig. 3) has been made. The significant simulation results are collected in Table 4, and shown in Fig. 7. From these results it follows that the proposed mapping with optimized voltage patterns has several advantages In comparison to SCC: the number of switches involved in voltage vector switch-over and the number of voltage vector changes are reduced by 60 % and 40 % respectively, chattering of iSq is reduced by 40 %, reduction of (¿s ),,,„. 1,73 % slightly reduces motor losses, the angular velocity range of the constant rotor field is doubled, tracking of kinematics variable is slightly improved. 400 -300 -200 -100 - Ž. Čučej, P. Cafuta, R. Svečko: PWM less current control at VSI-IM drive Informacije MIDEM 31 (2001 )2, str.74-83 Table 4: Simulation results. parameter SCC proposed nax (iSq) - min (iSq) [A] 20,26 10,83 L Sq [A] 12,51 12,62 (ls1 )„,„ [A] 13,39 12,97 max (iS9)-min(/S9)_ 1,62 0,87 max(iSd)-min(iw) [A] 4,92 5,96 he [A] 0,93 0,57 ('S'l )r„u [A] 1,98 2,17 (h) ' ' rms [A] 13,39 13,15 u changes frequency total switch-over freq. [Hz] [Hz] 19800 48200 11400 18800 end position error A
» s 0. Moreover, the stator windings resistance in IM is usually low, and the term -/?4.i0 can be neglected. Furthermore, considering that during the sampling interval is constant, its derivation is zero. From (31) it follows that d0 - e0. Hence, the simplified model Lsaso(P) = uko(P)-eo is assumed in presented design. (32) Considering simplified IM model (2) at constant rotor field, where pimR = 0 and consequently ekl = 0, condition (33) can be written as: y =f- [> (P) - edq ] + ^ [ukq (p)- eiq - edq ] < 0 L 'Sa (34) In the case of selected zero voltage vectors (34) becomes: y Lsa Sa (35) and it is also evident that it is negative as long as p ^ 0 and the condition (19) for selecting of zero voltage vectors is fulfilled. In the case of p = 0, (34) is equal to zero, meaning that the system is at a standstill. But there is an assumption for neglecting the influence of Rs for simplified IM model is not valid anymore, consequently full IM model had to be considered in (33). Assuming selection of zero voltage and that during sample interval i*Eh is constant, (35) becomes: y = L, ~Rshd h — Rshg 'Sa (36) which is negative until the condition (10) is satisfied, since according to (19) signs of sq and eq are reciprocal. Those facts can serve as proof of the following theorem: Theorem: Zero voltage maintains sliding along switching lines, or limit cycle around the error plane origin, if and only if their use satisfies the conditions of (10) and (19). Žarko Cučej, Peter Cafuta, and Rajko Svečko University of Maribor, Slovenia e-mail: zarko.cucej@uni-mb.s D. Stability analysis For attraction domain Aq the reaching condition is derived by second Lyapunov method /9/ from quadratic form |ssr, V>0 as: Prispelo (Arrived): 24.03.2001 Sprejeto (Accepted): 01.06.2001 83 Informacije MIDEM 31 (2001 )2, Ljubljana UDK621,3:(53+54+621 +66), ISSN0352-9045 TESTABILITY ISSUES OF SYSTEM-ON-CHIP DESIGN Franc Novak Institut "Jožef Stefan", Ljubljana, Slovenia Keywords: microelectronics, SOC, System-On-Chip, SECT IEEE P1500, Standards for Embedded Core Test, design, testability, IC, integrated circuits, embedded cores, core wrapper, computer languages, CTL, Core Test Languages, testing strategies, TAM, Test Access Mechanisms, STAM, Serial Test Access Mechanisms, Automatic Test Equipment, BIST, Built-in Self-Test, STIL IEEE P1450, Standards Test Interface Language IEEE P1450, WIP, Wrapper Interface Port, WIR, Wrapper Instruction Registers, WBR, Wrapper Boundary Registers Abstract: The paper describes current trends in standardisation of design-for-testability approaches for complex circuits with embedded cores also referred to as system-on-chip. The concept of core wrapper and the corresponding core test language, the main two issues of the forthcoming IEEE P1500 Standard, are briefly Introduced. Possible strategies for test Integration of cores conforming to the standard are discussed. References to the available IEEE P1500 Standard documents and papers are given. The goal of the paper was to enlighten the issues that may be of most interest to a potential user/designer in the applications of our national electronic industry. Upoštevanje zmožnosti testiranja pri načrtovanju sistema-v-čipu Ključne besede: mikroelektronlka, SOC sistem-v-chip-u, SECT IEEE P1500 standardi za preskušanje jeder vgrajeno, snovanje, preskusljivost, IC vezja integrirana, jedra namenska, ovoj jedra testni, jeziki računalniški, CTL jeziki za opis preskušanja jeder, strategije preskušanja, TAM mehanizmi dostopa za testiranje, STAM mehanizmi dostopa za preskušanje serijski, ATE oprema za preskuse avtomatska, BIST preskušanje vgrajeno vase, STIL IEEE P1450 standardi za jezik preskuševalni vmesniškl, WIP vrata ovoja vmesnika, WIR registri ovoja inštrukcijski, WBR registri ovoja mejni Povzetek: V članku opisujemo sedanje smeri razvoja standardizacije postopkov načrtovanja zmožnosti testiranja kompleksnih vezij z vgrajenimi namenskimi jedri, imenovanih tudi slstem-v-čipu. Na kratko sta opisana zasnova testnega ovoja jedra in jezik za opis testiranja jeder, ki predstavljata glavni značilnosti prihajajočega standarda (EEE P1500. Opisane so strategije povezovanja jeder, ki ustrezajo standardu, v sistem, ki ga bo možno učinkovito testirati. Navedene so reference na dokumente o standardu IEEE P1500 dosegljive preko spletne strani delovne skupine ter objavljene članke in referate. Cilj prispevka je osvetliti tiste vidike standarda, ki bi bili najzanimivejši za potencialnega uporabnika/načrtovalca v aplikacijah domače elektronske industrije. 1 Introduction Recent technology advances allow to integrate functions that have been traditionally implemented on one or more complex printed circuit boards into one single IC, often referred to as system-on-chip (SOC). The development of this new class of ICs is based on the design technique which integrates large reusable blocks (i.e. cores) that have been designed and verified in earlier applications in practice, /1 /. A core may be soft, firm or hard, /1 /-/4/. A soft core is a synthesizable register-transfer level code of a logic block. It allows much flexibility to the designer and can be realised by different technological processes. A hard core consists of a technology-dependent layout and lacks flexibility since it has been optimised for a given performance requirements. A firm core contains a gate-level netlist that is ready for placement and routing and thus represents a compromise between the two. Embedded cores provide a wide range of functions, like CPUs, DSPs, interfaces, controllers, memories, and others. The advantage of embedding reusable cores in the design of a new product is a shortened design cycle resulting in reduced time-to-market and reduced cost. The design of a complex system-on-chip normally requires expertise in different technology areas which is difficult to find in a single design house. Consequently, embedded- core design involves two parties: core providers and core users. In most cases, the core user (i.e., system integrator) does not have the knowledge about the design of the building blocks (cores). It is neitherthe interest of core providers to reveal design and implementation details in order to protect their intellectual property. However, the core user is responsible for manufacturing and testing the whole system-on-chip Including cores, interconnect logic and possible additional user-designed logic. Complexity of the design and limited knowledge about implementation of cores make the problem of SOC testing rather challenging to the core user. The problem could only be adequately handled by involving both core providers and core users in a joint effort to develop efficient test solutions. In order to provide an independent openly defined design-for-testability method for Integrated circuits containing embedded cores, an initiative to develop a standard has been taken by the IEEE P1500 Working Group, /6/. 2 Testing of core-based chips The SOC designer (core user) has limited knowledge about the adopted cores and he cannot develop adequate tests for them. The core providers need to provide tests for the cores and all the necessary information (i.e., test patterns, timing and protocol description). A SOC normally consists 84 F. Novak: Testability Issues of System-on-chip Design Informacije MIDEM 31(2001)2, str. 84-87 of cores from different providers and the integration of different core tests into a composite SOC test may become a difficult job because of the diversity of descriptions and test implementation details. Core internal tests need to be described in a commonly accepted way. The forthcoming IEEE P1500 standard defines standard format (i.e., Core Test Language) for the description of core test /6/. Conventional production test of assembled boards consists of a sequence of separate component tests, bare board test, static test of assembled board (detecting shorts and opens) and dynamic functional test (detecting timing faults). In the case of testing SOC, all the above tests are merged into one composite test instance. Furthermore, in most cases direct access to the core terminals is not provided which makes it difficult to run internal tests of deeply embedded cores. The principle of embedded core testing is presented in terms of conceptual test architecture /3/ consisting of test pattern source and sink, test access mechanism (TAM) and core test wrapper (Figure 1). In order to test a core, a test source (i.e., test pattern generator) generating test stimuli and a test sink (i.e., response compactors, current monitors, etc.) collecting the test responses must be provided. Test access mechanism transports test patterns from the source to the core and test responses from the core to the test sink. Finally, the core test wrapper, a thin shell around the core, provides interface between the embedded core and its environment. It connects the terminals of the core to the rest of SOC (in the normal mode) and to the test access mechanism (in the test mode). The IEEE P1500 Standard defines the structure and the operation of the test wrapper /6/. Figure 1: Embedded core testing involves source, sink, TAM and wrapper The described test architecture is implemented in various ways depending on the type of the core (i.e., logic, memory, analog or mixed-signal), type of pre-defined tests provided by the core vendor, and required test quality. For example, test patterns can be generated by external auto-matic-test-equipment (ATE) or built-in self-test (BIST) logic implemented in SOC. Likewise, test results can be evaluated by external ATE or compressed to a signature and compared to a reference value by the BIST logic on SOC. More details on this are given in Zorian et at. /3/. 3 IEEE P1500 Standard for Embedded Core Test (SECT) Activities on IEEE P1500 SECT started in 1995, and have been officially approved by the IEEE Standards Activities Board in 1997. The work currently focuses on a standard for testing digital logic and memory cores, future extensions will include also analog and mixed-signal cores. The mission statement defines the following scope /6/: "This project will develop a standard test method for Integrated Circuits containing embedded cores, i.e. reusable megacells. This method will be independent of the underlying functionality of the Integrated Circuit or its individual embedded cores. The method will create the necessary testability requirements for detection and diagnosis of such integrated Circuits, while allowing for ease of interoperability of cores originated from distinct sources. This method will be usable for all classes of digital cores including hierarchical ones." The two primary issues are to provide means for (1) efficient core test knowledge transfer, and (2) the test access to the embedded cores. Accordingly, the standard defines (1) a language for the description of the test-related information for the cores embedded in the SOC, and (2) the test wrapper architecture of the embedded core. The work on the standard has progressed to the draft version IEEE P1500/D0.3 and aims to be ready for ballot in 2001 /6/. 3.1 Core test language IEEE P1500 SECT defines the Core Test Language (CTL) in order to facilitate the transfer of the core test-related information from the core providerto the core user. CTL uses the syntax of IEEE 1450, Standard Test Interface Language (STIL), /7/, and describes test information including test data, test methodology, core configurations and necessary connectivity information for system integration. The objective is to provide all the necessary information for the implementation of core wrapper including the description of core signals, timing, electrical characteristics, core external connections, protocol for applying test patterns to the core terminals, etc. Detailed description of CTL is beyond the scope of this paper. Interested readers can find more information on this subject together with an illustrative example describing the way of transforming a bare core into a 1500-compliant core in /4/. 3.2 Core test wrapper Test wrapper is a thin shell around the core and serves as an interface between the core and the test access mechanism(s). During normal operation, wrapper connects core inputs and outputs to SOC functional wires. For testing purposes, wrapper has modes in which core inputs 85 Informacije MIDEM 31(2001)2, str. 84-87 F. Novak: Testability Issues of System-on-chip Design and outputs are connected to a mandatory serial TAM (one-bit wide) and optional scalable parallel TAMs which provide access for core-internal and core-external tests. Wrapper operation is controlled by a set of control and clock signals provided at the Wrapper Interface Port (WIP). WIP also includes serial scan terminals WSI and WSO which are used to shift-in and shift-out serial test data. (The function of WSI and WSO is similar to TDI and TDO terminals of IEEE 1149.1, digital boundary-scan architecture /8/). Test wrapper contains the following mandatory registers: wrapper instruction register (WIR) which is similar to IEEE 1149.1 instruction register and controls the operation of the wrapper. WIR receives instructions via wrapper serial input WSI. wrapper boundary register (WBR) to which the core functional terminals are connected. It is a serial shift register similar to the IEEE 1149.1 boundary-scan register. One-bit bypass register which is similar to IEEE 1149.1 bypass register. It is used to bypass the WBR. In a single scan path configuration, where WSI and WSO terminals of cores are connected in series, it may become inconvenient to shift data through the entire sequence of WBRs. Bypass registers enable to skip out the WBRs of the cores that are not being tested. Figure 2: Test wrapper structure Serial TAM and (if available) parallel TAMs provide means for performing core-internal and core-external tests. Core-Internal test is based on the test information that the core user gets from the core provider. It may consist of the application of test patterns within a specified test protocol, or of initiation of a built-in self-test of the core. Core-external test checks external connections between the cores and additional glue logic designed by the SOC integrator. For the core-internal tests, test stimuli are provided via TAM to wrapper boundary at the core input terminals and test results are read via TAM from the wrapper boundary at the core output terminals. For the core-external tests, initial logical values are set-up via TAM at the wrapper boundary at the core output terminals and results are observed at the wrapper boundary at the core input terminals. 4 Possible test configurations From the conceptual point of view one may notice several points of similarity between IEEE P1500 SECT and IEEE 1149.1. For example, wrapper registers WIR, WBR and bypass have similar role as instruction, boundary-scan and bypass register in IEEE 1149.1. Furthermore, as mentioned above, the function of WSI and WSO is similar to TDI and TDO in digital boundary-scan architecture. But there are also substantial differences: the operation of the TAP Controller which is the "heart" of the IEEE 1149.1 compliant circuit is given by the state diagram which unambiguously defines the test protocol - on the other hand, IEEE P1500 SECT does not define the operation of the test wrapper by a state diagram, and allows the designer of a test wrapper a lot of freedom. SOC integrator can choose different strategies of implementing STAM and parallel TAMs of individual wrappers depending on the complexity of core-internal tests, the amount of additional user defined logic, overall complexity of the SOC and on the conditions imposed by the available ATE that will be used in production test. For example, for a core with a built-in self-test it may be sufficient to provide test wrapper only with STAM. On the other hand, some other core may need extensive amount of test patterns that can only be transferred in reasonable time via parallel TAM. Wrappers can be connected in different configurations (i.e., multiplexing, daisychain, etc.) differing in test time, wiring and SOC performance. Besides, possible implementation of boundary-scan at the level of individual cores and requirements for its implementation at the level of SOC will impact the selection of wrapper test features and system level core configurations. Effective combination of IEEE 1149.1 and IEEE P1500 SECT infrastructure in SOC test Is an interesting problem in practice. 5 Conclusion SOC testing is one of the current hot topics in the field of electronic test. Several papers and vivid discussions at recent European Test Conference /9/ confirm the importance of providing efficient solutions to the problem of testing embedded cores integrated in a complex SOC. In the paper, the basic approach to testing SOC formalised in IEEE P1500 SECT is described. Another issue concerns intellectual property of core providers. Due to the opposite interests of core providers and core users regarding the level of the core implementation details that should be revealed to the user (making SOC testing easier) the problem of information transfer remains a challenge for both participating parties. Here again, IEEE PI500 SECT offers means that may help them in achieving a reasonable solution. 86 F. Novak: Testability Issues of System-on-chip Design Informacije MIDEM 31(2001)2, str. 84-87 Finally one could ask: what consequences will the forthcoming IEEE P1500 SECT have to those users that do not produce complex SOC but rather use them in their products? We can expect from the SOCs producers to provide some information related to testing embedded cores in a SOC for the purpose of debugging and for performing system functional test. Besides, cores including scalable test wrapper are likely to become a standard product on the market, ready for integration as well in simple electronic systems (e.g., intelligent sensors) which makes the IEEE P1500 SECT interesting to a broader group of potential users. Literature /1/ R.K.Gupta, Y.Zorian, "Introducing core-based system design", IEEE Design and Test of Computers, Vol. 14, No. 4, October-December 1997, pp. 15-25. /2/ Y.Zorian, "Test requirements for embedded core-based systems and IEEE P1500", Proc. International Test Conference, Washington, DC, November 1-6, 1997, pp. 191-199. /3/ Y.Zorian, E.J.Marinissen, S.Dey, "Testing embedded-core based system chips", Proc. International Test Conference, Washington, DC, October 18-23, 1998, pp. 130-143. /4/ E.J.Marinissen, Y.Zorian, R.Kapur, T.Taylor, L.Whetsel, "Towards a standard for embedded core test: an example", Proc. International Test Conference, Atlantic City, NJ, September 28-30, 1999, paper 24.1. /5/ E.J.Marinissen, R.Kapur, Y.Zorian, "On using IEEE P1500 SECT fortest plug-n-play", Proc. International Test Conference, Atlantic City, NJ, October 1-5, 2000, paper 24.1. /6/ IEEE P1500 Standard for Embedded Core Test: http:// www.manta.ieee.org/groups/1500/ /7/ T.Taylor, G.Maston, "Standard Test Interface Language (STIL): A new language for Patterns and waveforms", Proc. International Test Conference, Washington, DC, October 20-25, 1996, pp. 565-570. /8/ IEEE Std 1149.1-1990: IEEE Standard Test Access Port and Boundary-Scan Architecture. /9/ Proceedings of European Test Workshop ETW2001, Stockholm, May 29 - Junel, 2001. Franc Novak Institut "Jožef Stefan" Jamova 39, 1000 Ljubljana, Slovenia tel. +386 1 4773 386 fax. +386 1 2519 385 Email: franc.novak@ijs.si Prispelo (Arrived): 18.05.01 Sprejeto (Accepted): 01.06.01 87 Informacije MIDEM 31(2001)2, Ljubljana UDK621,3:(53+54+621 +66), ISSN0352-9045 DODATNI PRIMERJALNI TESTI ZA SIMULATORJE SPICE Tomaž Dogša Fakulteta za elektrotehniko, računalništvo in informatiko, Univerza v Mariboru Ključne besede: SPICE orodja računalniška, testi primerjalni, simulatorji računalniški, točke delovne, DC analize enosmerne, testiranja avtomatska, avtomatizacija testiranja, vezja naključna Povzetek: Dosedanji primerjalni testi, s katerimi lahko primerjamo kakovost simulatorjev, temeljijo na posebej izbrani majhni množici vezij. V prispevku predlagamo dodatne skupine primerjalnih statističnih testov in kriterije, s katerim bi lahko na objektiven način primerjali kakovost simulatorjev električnih vezij. Vsa vezja, ki so vključena v dodatno množico testov imajo naključno tvorjeno strukturo in naključno izbrane elemente in parametre. Ker lahko s posebnim generatorjem vezij tvorimo poljubno število takih vezij, je možno podajati statistično ovrednotena kvantitivna merila glede kakovosti simulatorjev. Additional Benchmark Tests for SPICE Simulators Keywords: SPICE computer tools, Simulation Program with Integrated Circuit Emphasis computer tools, benchmarks, comparative tests, computer simulators, biases, operating points, DC analyses, Direct Current analyses, automatic testing, test automation, random circuits Abstract: The purpose of benchmark test is to compare the quality attributes of circuits simulators. Existing benchmark tests are based on selected small set of electronic circuits. In this paper we propose additional sets of statistically based benchmark tests and corresponding criteria that enable unbiased comparison. All test circuits that form additional benchmark sets have randomly generated structure, randomly chosen elements and their parameters. Statistically quantization of quality attributes is now possible, since high number of circuits can be generated by the special software tool. 1. Uvod Načrtovanje elektronskih vezij brez pomoči računalnika je danes praktično neizvedljivo. Vse večja kompleksnost vezij in nelinearnost elektronskih elementov v večini primerov onemogočajo analitični pristop. Načrtovalci si v takih primerih pomagajo s simulatorji elektronskih vezij. Simulatorji so zelo kompleksni programski paketi, ki se neprestano spreminjajo: izboljšujejo se uporabljeni algoritmi in modeli ter dodaja se nova funkcionalnost. Eden izmed glavnih namenov simulatorja je napovedovanje obnašanja realnega vezja. Kljub relativni zrelosti simulatorjev, se dogaja, da dajejo napačne rezultate (glej npr. /PERŠIČ.1995/). Na tržišču obstaja več vrst simulatorjev, ki se med seboj razlikujejo po funkcionalnosti, uporabljenih algoritmih in modelih, ceni in drugih atributov kakovosti. Njihova medsebojna primerjava temelji na določenih primerjalnih testih (benchmark). Kaj je primerjalni test? Davidson in Harlow v svojem uvodniku /DAVIDSON,2000/ ponujata delno prirejeno definicijo, ki jo lahko najdemo v leksikonu Merriam-Webster Collegiate Dictionary: "Primerjalni test je standardiziran problem (vezje ali del vezja), ki ga uporabljamo za primerjavo zmogljivosti (hitrost, učinkovitost, kakovost rezultata) različnih orodij in algoritmov". Namen primerjalnih testov ni samo primerjanje izbranih karakteristik (npr. hitrosti) ampak širši vpogled v kakovost simulatorja. Zaradi tega so tudi zanimivi za načrtovalce in preverjevalce EDA (Electronic Design Automation) programske opreme. S primerjalnimi testi lahko testirajo simulatorje ali pa jih uporabijo za merjenje uspešnosti novih ali izboljšanih algoritmov. Vsak primerjalni test mora biti sestavljen iz opisa postopka, opisa testnih primerov in kriterijev za vrednotenje primerjave. Testne primere tvorijo vhodni podatki in pričakovani rezultati oziroma pričakovano obnašanje. Primerjalni testi naj bi predstavljali reprezentativne primerke iz posameznih problemskih razredov. Npr. zelo znana zbirka 58 vezij, ki so jo leta 1990 predlagali na eni izmed delavnic na MCNC (Microelectronic Center of North Carolina. (http://www.cbl.ncsu.edu/), je sestavljena in petih skupin. Te skupine lahko glede kompleksnosti vezij razdelimo v dve grupi: skupina majhnih (približno do 500 elementov) in skupina obširnejših (nad približno 1000 elementov) vezij. Vezja so tako izbrana, da pokrivajo celotno problemsko domeno. Slabost sedanjih primerjalnih testov oziroma metod kritizira tudi F. Brglez /BRGLEZ,2000/. Zavzema se za znanstveni pristop na področju eksperimentiranja, kar pomeni, da se ne oziramo na nekaj izbranih testnih vezij ampak na množico. S statistično analizo nato ovrednotimo rezultate eskperimenta oziroma primerjalne analize. Zato predlagamo, da se obstoječemu nizu primerjalnih testov dodajo še tri skupine. Tako bi za potrebe primerjalne analize in testiranja uporabljali naslednje skupine: 1. skupina: izbor posameznih konkretnih vezij (obstoječa skupina), 2. skupina: množica naključno generiranih topološko pravilnih vezij, 3. skupina: izbor posameznih topološko nepravilnih vezij, 4. skupina: množica naključno generiranih topološko nepravilnih vezij. Vključitev skupine s topološko nepravilnimi vezji je smiselna zaradi tega, ker pri takih vezjih rešitev (niti teoretična) ne more obstajati in nas mora o tem simulator obvestiti. V pris- T. Dogša: Dodatni primerjalni testi za simulatorje SPICE Informacije MIDEM 31(2001)2, str. 88-93 pevku bomo najprej opisali določeno problematiko, ki je povezana z naključnim generiranjem vezij. Kljub temu, da se bomo omejili, le na simulatorje analognih vezij to še ne pomeni, da predlaganih idej ni možno posplošiti na digitalna in analogno-digitalna vezja. Vsak simulator nudi uporabniku več vrst analiz. Najbolj osnovna je vsekakor analiza delovne točke. Ker predstavlja izhodišče za skoraj vse druge analize, smo se osredotočili samo na njo. Torej, zanimali nas bodo primerjalni testi, s katerimi bi lahko ovrednotili uspešnost algoritmov za analizo delovne točke. Najprej bomo na kratko opisali probleme, ki se utegnejo pojaviti pri analizi delovne točke nato pa problematiko generiranja naključnih vezij. Za ilustracijo bomo prikazali tudi konkretne rezultate primerjalne analize za tri simulatorje: SPICE2G6 (verzija Intusoft IS SPICE 1.41 12/12/87, PSPICE (verzija 3.01, januar 1987) in SPICE3F4 (verzija 18. februar 1999). Izbor je bil povezan predvsem z njihovo dosegljivostjo. Če bi uporabili najnovejše verzije, bi zagotovo dobili drugačne rezultate. 2. Delovna točka Delovna točka je niz takšnih parov enosmernih tokov in napetosti, ki hkrati zadoščajo karakteristiki elementov in obema Kirchhoffovima zakonoma. Ker gre za enosmerno analizo, simulator najprej pretvori vezje v rezistivno variantno in nato izvede simulacijo. Vsi algoritmi, ki jih uporabljajo simulatorji analognih vezij za analizo delovne točke, temeljijo na določenih iterativnih metodah, ki jih omejimo s številom iteracij in zahtevano natančnostjo rezultata. Pri analitičnem ali grafičnem izračunu vidimo, da lahko obstaja ena, več ali pa nobena rešitev (slika 1 a in b). 'A ''A Slika 1 Zgled grafične analize dveh vezij, ki sta sestavljeni iz baterije, upora in nelinernega elementa.Vezje (a) tri teoretične rešitve, vezje (b) nima teoretične rešitve Več rešitev več ne moremo interpretirati kot rezultat enosmerne analize, ampak kot stacionarno stanje prehodnega pojava električnega vezja. Rešitev torej ni odvisna samo od vezja in nastavitev parametrov, s katerimi vplivamo na algoritem, ampak tudi od začetnih pogojev. Ena izmed slabosti tipičnih simulatorjev analognih vezih (npr. SPICE) je ta, da izračunajo samo eno delovno točko, kljub temu, da obstaja več rešitev. Obstajajo tudi simulatorji, ki z uporabo popolnoma drugačnih algoritmov, izračunajo vse delovne točke oziroma ravnotežna stanja. Najbolj znani metodi sta: iterativna odsekoma-linearna kombinacijska analiza /CHUA, 1975/ In homotopna metoda /TRAJKOVIC.1991/. Sled- nja je tudi implementirana v simulatorju HomSPICE /TRA-JKOVIC.1998/, ki pa ga nismo uspeli preizkusiti. Eden izmed pogojev, da bo simulator poiskal delovno točko, je obstoj teoretične rešitve. Neobstoj teoretične rešitve se lahko pojavlja samo pri vezjih, ki vsebujejo enega ali več nerealno modeliranih elementov. Glede oblike enosmernih karakteristik modelov ni nobenih omejitev razen za vrednosti toka oziroma napetosti, ko le-ta limitira proti neskončnosti. Ker vedno obstaja neka delovna točka, pri kateri postane vezje totalno pasivno, pomeni, da se morajo karakteristike dvopolnih elementov začeti v prvem in končati v tretjem kvadrantu. Takoj vidimo, da idealni napetostni in tokovni vir te zahteve ne izpolnjujeta. Ta problem lahko simulator reši z dodajanjem ustreznega upora k vsakemu napetostnemu ali/in tokovnemu viru in z dodatnimi zahtevami glede topologije (npr. zanka iz samih napetostnih virov je prepovedana). Če karakteristika vsakega elementa zadosti prej omenjenemu kriteriju, potem vedno obstaja teoretična rešitev. Če vsaj en element tega kriterija ne izpolnjuje, se lahko zgodi, da teoretična rešitev ne obstaja (slika 1 b). Vsa pravkar opisana problematika se uporabniku kaže v neuspešnosti analize, ki se večinoma navzven pokaže kot nekonvergiranje rešitve. Problem konvergence je možno reševati na več načinov: 1. Simulatorju pomagamo s podatkom o približni rešitvi (stavek .NODESET). 2. Spremenimo modele - uporabimo realnejše modele. 3. Spreminjamo razne parametre, s katerimi vplivamo na potek reševanja (npr. povečamo največje število iteracij). 4. Uporabimo počasi naraščajoče napetostne vire (source-stepping algorithms). 5. V vsako vozlišče dodamo parazltno prevodnost, ki jo počasi manjšamo (Gmin -stepping). 6. Z dodanimi parazitnimi reaktivnimi elementi pretvorimo vezje v dinamično in simuliramo vklop vezja (pseu-do-transient analysis). 7. Izberemo drugačen algoritem za analizo delovne točke (uporabimo npr. odsekoma-linearno kombinacijsko analizo ali homotopno metodo). Pravilnost izračuna delovne točke je odvisna od pravilnosti uporabljenih modelov in pravilnosti ter učinkovitosti algoritma. Pri sodobnih simulatorjih je lahko vzrok za napačen Izračun delovne točke tudi v napačnem delovanju post-procesorja. Vtem primeru jedro simulatorja izračuna pravilno vrednost, grafični postprocesor jo pa izpiše napačno. 3. Odpoved simulatorja pri izračunu delovne točke Izračun delovne točke je ena izmed temeljnih analiz, ki jih izvaja simulator. Nepravilnosti pri izračunu delovne točke vplivajo na pravilnost večine analiz (npr. .AC, .TF, .DC, .TRAN). Potem, ko smo sprožili zahtevo za analizo delovne točke, lahko simulator preide v naslednja stanja: 89 Informacije MIDEM 31(2001)2, str. 88-93 T. Dogša: Dodatni primerjalni testi za simulatorje SPICE 1. Delovna točka je izračunana in se nahaja znotraj dovoljenih odstopanj pričakovane vrednosti. 2. Delovna točka je izračunana vendar se ne nahaja znotraj dovoljenih odstopanj pričakovane vrednosti. V tem primeru gre za alternativno delovno točko oziroma za vezje, ki ima več delovnih točk. Možno je tudi, da simulator deluje nepravilno. 3. Delovna točka ni izračunana, kljub temu da ima vezje pravilno topološko strukturo (npr. rešitev ne konvergi-ra ali pa nastopi popolna odpoved simulatorja) 4. Delovna točka ni izračunana, ker ima vezje nepravilno topološko strukturo (npr. zanka iz samih napetostnih virov). Stanje številka 3 bomo klasificirali kot odpoved. Popolna odpoved simulatorja se pojavi takrat, ko delovanje programa nasilno ustavi operacijski sistem. Za firmo, kije izdelala simulatorje to sicer zelo neprijetna odpoved, za uporabnika pa zgolj moteča in hkrati nenevarna, saj je le-ta z odpovedjo seznanjen. Kritične oziroma fatalne so lahko tiste odpovedi, katerih uporabnik ne opazi. To se lahko zgodi, če ne razpolaga s pričakovano vrednostjo oziroma je interval, v katerem pričakuje rezultat, prevelik. 4. Naključno analogno vezje Naključna vezja lahko generiramo na dva načina. Postavimo nek splošen model, ki ustreza neki skupini vezij in nato s spreminjanjem parametrov in nekaterih delov strukture tvorimo množico naključnih vezij. Zgled za to metodo bi lahko bil npr. splošen model enostopenjskega diferenčnega ojačevalnika, ki vključuje tudi nekaj variant. Pri drugi metodi naključno generiramo graf vezja in nato elemente. S to metodo lahko v bistvu nastane katerokoli možno vezje, pri prvi pa smo omejeni z izbranim splošnim modelom. Za generiranje naključnih vezij smo izdelali poseben program (generator naključnih vezij), ki delno združuje oba pristopa. Naključno vezje, ki ga tvori generator, je sestavljeno iz stalnega in naključnega dela. Najpomembnejši podatki, ki vplivajo na strukturo naključnih vezij in vrednosti parametrov, so: 1. Deleži posameznih elementov in njihovi parametri (R, L, C, E, G, I, V, D, NMOS, PMOS, QN, QP). E in G sta polinomska vira, ki ju uporabljamo za modeliranje krmiljenih virov oziroma nelinearnih dvopolov. Parametri so: največja in najmanjša vrednost ter vrsta porazdelitve. Trenutna verzija ne omogoča naključni izbor parametrov v .MODEL stavkih. 2. Kompleksnost vezja (število vozlišč, število elementov). 3. Odločitev o generiranju topološko pravilnih ali nepravilnih strukturah. 4. Izbor porazdelitvene funkcije po kateri se vrši izbor naključnih entitet (Gaussova, konstantna ali kaotična porazdelitev). 5. Statistična privilegiranost dveh vozlišč. Pri večini realnih vezij lahko vidimo, da incidenčna matrika ni ena- komerno napolnjena oziroma nekatera vozlišča izrazito odstopajo glede števila priključenih elementov. To sta vozlišči, kamor je priključena napajalna napetost in masa (glej sliko 3). Na videz je funkcija generatorja podobna tisti, ki se uporablja pri Monte Carlo analizi. Razlika je v tem, da tukaj naključno spreminjamo strukturo vezja, elemente in parametre, medtem ko pri Monte Carlo analizi samo vrednosti parametrov. Glede na izbor podatkov, ki so vhod v generator, lahko generirarmo zelo pestro množico vezij. Z nelinearnimi upori, ki so implementirani z G viri (za SPICE3 se uporablja B element), generator simulira uporabo zunanjih vedenjskih modelov. Z izborom lihe oziroma sode stopnje polinoma generiramo teoretično nemogoče (npr. element na sliki 1 b) oziroma mogoče nelinearne upore (npr. element na sliki 1 a). S temi upori lahko tudi spreminjamo nelinearnost vezja. Zgled naključno generiranega vezja prikazujeta sliki 2 in 3. stalili del vezja naključno generiran del vezja Slika 3 Shema naključno generiranega analognega vezja narisanega na podlagi opisa iz slike 2. Stalni del vezja je enak za vsa generirana vezja. 5. Rezultati primerjalnega testiranja Vsako testiranje izvajamo po naslednjih korakih: tvorjenje testnih vzorcev, tvorjenje pričakovih vrednosti, izvedba analize in vrednotenje rezultatov. Vse korake razen drugega je relativno enostavno avtomatizirati. Za avtomatizacijo drugega koraka moramo napraviti zahteven program za sintezo vezja. V primeru testiranja več simulatorjev imamo tudi možnost, da enega izberemo za referenčnega. Glede na predlagane skupine vezij namenjenih primerjalnemu testiranju, smo izvedli samo testiranje z množico naključno generiranih topološko pravilnih vezij. 90 T. Dogša: Dodatni primerjalni testi za simulatorje SPICE Informacije MIDEM 31(2001)2, str. 88-93 Tabela 1 Opis testnih vezij Testna garnitura število vezij opis 1 169 vsi elementi, brez nelinearnih uporov 2 200 samo NMOS, PMOS, D, R in napajalni viri 3 199 samo QN, QP, D, R in napajalni viri 4 169 vsi elementi, nelinearnost uporov do 4.stop. 5 169 vsi elementi, nelinearnost uporov do 3.stop. 6 168 vsi elementi, nelinearnost uporov do 2.stop. 7 106 brez polprevodnih elementov, nelinearnost uporov do 4.stop % 100,00 80,00 60,00 40,00 20,00 I 0,00 Delež uspešno zaključenih simulacij Espice2g6 £3 pspice □ spice3f4 sKupina testov Slika 4 Delež uspešno zaključenih simulacij Ker bi opis in diskusija rezultatov za vse primerjalne teste presegala dovoljen obseg prispevka, se bomo osredotočili le na sedmo garnituro testov, v kateri ni nobenih polprevod-nih elementov. S tem smo izločili morebiten vpliv kakovosti VEZ117.cir *SPICE_NET *Stevilka vezja: * 117 *Datum nastanka: 4.4.2001 Generator vezij:V5.0 2.4.2001 *Konfiguracijska datoteka: k4g2kl.dat *Nastanek konfiguracijske datoteke: 4.4.2001 12:32:24 *Verzija opisovanja nel. elementov:2 Število vozlišč: 6 Število el,: 14 *Nacin generiranja vezja: naključno *Statisticno poudarjeno vozlišče: 0 20.00% *Statisticno poudarjeno vozlišče: 1 20.00% R1 0 5 1.04222864689678E+0004 R2 1 3 1.64998529084921E+0004 R3 2 0 7.76117287476063E+0004 V4 3 2 -9.63017179630697E+0000 R5 4 1 5.58461088487506E+0003 E6 5 1 POLY(1) (4 6) 3.88584041036665E-0001 -4.95419465005398E + -1.17212752811611E-0001 -5.41528668254614E- -0002 + -6.52 68228 6687195E-0001 G7 6 5 POLY{1) (6 5) -1.81034177541733E-0001 + -4.58973378874362E-0001 + 2.831490989774< 47E-0001 QN8 4 0 1 QN R9 1 4 3.21886612679362E+0004 E10 6 1 POLY(1) (2 1) -3.01108809188008E-0001 + -5.59775688685477E-0001 + 4.59779966622591E-0001 QP11 1 3 3 QP G12 0 1 POLY(1) (0 1) -6.98641702532768E-0001 5 . 45442000962794E-0001 + 8.75892678275704E-0001 -1.84644504450262E-0001 -1.96733874827623E-0001 MP13 10 11 PENH L=8U W=7U QN14 1 2 2 QN * OP * ======= Dodana datoteka : MOD_VSI.MOD ================ * Posebej dodamo nap. vir zato, da bo vedno prisoten vsaj en VDD 5000 0 5 RG 5000 1 1 •OPTIONS NOMOD ************************************************ ************** ********* ** ( MODEL M8CN-290) ** ** MCNC 0.8 CMOS PROCESS PISCES ** ** ( NOMINAL ) FEBRUARY 1990 ** ** SOURCE: CIRCUITSIM90 BENCHMARK CIRCUITS FILE MODELS.NOM ** ************************************************* Slika 2 Zgled naključno generiranega analognega vezja 91 Informacije MIDEM 31 (2001 )2, str. 88-93 T. Dogša: Dodatni primerjalni testi za simulatorje SPICE notranjih modelov in se osredotočili predvsem na učinkovitost algoritma za izračun delovne točke. Statistična porazdelitev elementov je bila naslednja: R (40%), V (10%), I (10%), G (20%), E (20%). Z napetostno krmiljenimi tokovnimi viri (G) smo realizirali nelinearne upore, katerih naključno generirana karakteristika je definirana s polinomom. Največja stopnja polinoma je bila 4. Podobno velja za krmiljen nelinearni napetostni vir E. Za vrednotenje primerjalnega testa smo postavili tri merila: merilo uspešnosti, merilo podobnosti in merilo ekskluzivnosti. Merilo uspešnosti je delež uspešno zaključenih simulacij. Za učinkovito primerjalno testiranje morajo biti testna vezja tako izbrana, da je uspešnost vedno manjša od 100%, sicer nastopi pojav nasičenja (merilo več ne zaznava sprememb). Če se uspešnost začne približevati 100%, je potrebno povečati število vezij oziroma stopnjo nelinearnosti. Zanimiva sta tudi atributa skupna napaka in število alternativnih rešitev. Razliko med referenčno in dejansko vrednostjo delovne točke vrednotimo s povprečnim kvadratič-nim pogreškom. Če je bil ta večji od nekega izbranega praga (5V), potem smo izračunano delovno točko vezja kvalificirali kot alternativno. Skupna napaka je vsota vseh napak vezij, ki so bila uspešno simulirana (izvzeta so bile alternativne delovne točke). To merilo je seveda problematično, saj je za naključno vezje težko podati enoten kriterij, ki bi omogočal identifikacijo alternativnih točk. Tabela 2 Podrobni rezultati za sedmo garnituro testov. SPICE2G6 PSPICE SPICE3F4 število neuspešnih simulacij 73% 56% 51% število uspešnih simulacij 27% 44% 49% skupna napaka 27V 31V - štev. altern. rešitev 2% 9% - Merilo podobnosti: s to metriko vrednotimo podobnost v obnašanju simulatorjev. Izračunamo ga kot kvocient med številom enakih stanj, v katero prideta dva simulatorja in številom testov. Če je podobnost med dvema simulatorjema enaka 1, pomeni, da sta bila uspešna in neuspešna pri enakih testnih primerih (vezjih). Pri testni garnituri številka 7 sta se SPICE3F4 in PSPICE v 87% testov obnašala enako (tabela 3). Tabela 3 Merilo podobnosti za sedmo garnituro testov. Merilo ekskluzivnosti: To merilo se nanaša na uspešnost tistih vezij, pri katerih je določen simulator odpovedal. Npr. SPICE2G6 je odpovedal pri 77 vezjih (tabela 4) in v množici teh vezij je PSPICE uspešno simuliral 23% vezij, SPICE3F4 pa 30%. Hkrati tudi vidimo, da vsa vezja, ki so povzročila odpoved simulatorja SPICE3F4, so tudi povzročila odpovedi ostalih simulatorjev. Ali z drugimi besedami, tam kjer SPICE3F4 ni uspel, nista uspela tudi ostala simulatorja. Z drugimi skupinami testov smo ugotovili, da to vedno ne velja. Npr. pri testni garnituri štev. 2 (tabela 5), je PSPICE uspel poiskati reštev za 37% vezij, za katere je bil SPICE3F4 neuspešen. Kljub temu lahko glede na vrednost ekskluzivnosti, še vedno lahko sklepamo, da je SPICE3F4 najboljši. Tabela 4 Merilo ekskluzivnosti za sedmo garnituro testov. spice2g6 pspice spice3f4 spice2g6 77 (100%) 18 (23%) 23 (30%) pspice 0 (0%) 59 (100%) 5 (9%) spice3f4 0 (0%) 0 (0%) 54 (100%) Tabela 5 Merilo ekskluzivnosti za drugo garnituro testov. spice2g6 pspice spice3f4 spice2g6 142 (100%) 84 (59%) 66 (46%) pspice 5 (8%) 63 (100%) 15 (24%) spice3f4 1 (1%) 29 (37%) 77 (100%) 7. Sklep Tradicionalno primerjalno testiranje temelji na izbrani majhni množici tipičnih vezij. Kervezja niso izbrana naključno in ker jih je premalo, ni možno uporabiti statističnih meril. Predlagamo, da se k obstoječi skupini dodajo še naključno generirana vezja. V tem primeru lahko uporabimo tri nova merila: merilo uspešnosti, podobnosti in ekskluzivnosti. Dva simulatorja sta enako kakovostna, če imata enako uspešnost, podobnost in ekskluzivnost. Pokazali smo, da predlagana merila in postopek testiranja večata objektivnost primerjalnega testiranja. Največji problem, ki nastopa pri testiranju, je določitev pričakovanih rezultatov (v našem primeru so to potenciali vseh vozlišč). Za vsako vezje bi bilo potrebno izračunati brez uporabe simulatorja delovno točko. Ker gre za naključna nelinearna vezja, ki niso vedno zaporedno-vzporedna, bi izračun delovne točke za npr. 1000 vezij predstavljal izredno naporno delo. Ta problem bomo skušali rešiti z nadgradnjo obstoječega generatorja naključnih vezij, ki lahko tvori naključna vezja tako, da si najprej izbere naključno vrednost delovne točke in nato napravi sintezo vezja. Zaradi težav pri sintezi, zanekrat niso vključeni polprevodni elementi, ampak samo linearni R, I, V in nelinearni G in E. spice2g6 pspice spice3f4 spice2g6 1 0,83 0,76 pspice 0,83 1 0,87 spice3f4 0,76 0,87 1 92 T. Dogša: Dodatni primerjalni testi za simulatorje SPICE Informacije MIDEM 31(2001)2, str. 88-93 8. Literatura /BRGLEZ.2000/ Franc Brglez "The Scientific Method and Design and Test", IEEE Design &Testof Computers, julij-september, 2000, str. 144,142,143. /CHUA,1975/ Leon O. Chua, Pen-Min Lin: " Computer-aided analysis of electronic circuits", Prentice-Hall, Englewood Cliffs, New Jersey, 1975. /CHUA.1976/ L. 0. Chua and A. Ushlda: "A switching-parameter algorithm for finding multiple solutions of nonlinear resistive circuits," IEEE Trans. Circuit Theory, Vol. CT-19, No. 4, str. 215-239,1976. /DAVIDSON,2000/ S. Davidson, J. Harlow: "Guest Editors' Introduction: Benchmarking for Design and Test", IEEE Design &Test of Computers, julij-september, 2000, str. 12-14. /PERŠIč,1995/ Boštjan Peršič: "Primer napačnega delovanja numer-ične integracije simulatorja SPICE", Elektrotehniški vestnik 62(2): 117-125, 1995. /TRAJKOVIC.1991 / Lj. Trajkovlc, R. C. Melville and S. C. Fang, "Finding dc operating points of transistor circuits using homotopy methods", Proc. IEEE Int. Symp. Circuits and Systems, Singapore, junij 1991, str. 758-761. (glej tudi http:// divine.eecs.berkeley.edu/~ljilja/). /TRAJKOVIC.1998/ Lj. Trajkovlc, E. Fung, and S. Sanders, "HomSPICE: Simulator with homotopy algorithms for finding dc and steady state solutions of nonlinear circuits",Proc. IEEE Int. Symp. Circuits and Systems, Monterey, CA, June 1998, TPA 10-2. Dr. Tomaž Dogša, Fakulteta za elektrotehniko, računalništvo in informatiko v Mariboru Smetanova 17 2000 Maribor, Slovenija Tel. (02) 220 7231 E- pošta: tdogsa@uni-mb.si Prispelo (Arrived): 25.04.01 Sprejeto (Accepted): 01.06.01 93 Informacije MIDEM 31 (2001 )2, Ljubljana UDK621,3:(53+54+621 +66), ISSN0352-9045 POWER ELECTRONIC BUILDING BLOCKS: A SURVEY Žarko ČUČEJ Univerza v Mariboru, Fakulteta za elektrotehniko, računalništvo in informatiko Key words: power electronics, PEBB, Power Electronics Building Blocks, development results, circuit topologies, electronic circuits, THD, Total Harmonic Distortion, PWM switches, Pulse Width Modulation switches, ZVT, Zero-Voltage Transition, ZCT, Zero-Current Transition, ZVS, Zero-Voltage Switching, ZCS, Zero-Current Switching, ARCP, Auxiliary Resonant Commutated Pole, inverters, converters, LMARC, Load Modulated Auxiliary Resonant Current, MCT, Metal-oxide silicon Controlled Thyristors, HM controllers, Hardware Manager controllers, AM controllers, Application Manager controllers, CI, Coordinated Interconnect, control, thermal losses Abstract: The PEBB program, sponsored by the Office of Naval Research, seeks to develop a general-purpose power controller capable of performing numerous electrical power conversion functions simply through software reconfiguration. Gradniki močnostne elektronike: pregled Ključne besede: elektronika močnostna, PEBB gradniki elektronike močnostne, rezultati razvoja, topologije vezij, vezja elektronska, THD popačenje harmonsko totalno, PWM stikala z modulacijo širine impulzov, ZVT prehod pri napetosti nič, ZCT prehod pri toku nič, ZVS preklapljanje pri napetosti nič, ZCS preklapljanje pri toku nič, ARCP pol komutirani z resonanco pomožno, inverterji, pretvorniki, LMARC tok pomožni resonančni moduliran z bremenom, MCT MOS kovina-oksid silicij tiristorji krmiljeni, HM krmilniki kot vodje hardware-ski, AM krmilniki kot vodje aplikacijski, Cl povezave medsebojne koordinirane, krmiljenje, izgube termične Povzetek: V članku je podan kratek pregled rezultatov razvoja gradnikov močnostne elektronike, ki ga je inicializiral Urad za raziskave pri ameriški vojni mornarici (ONR: Office of Naval Research). Za cilj so si zastavili razvoj pretvornikov, ki jih zgradimo s preprosto, standardizirano povezavo standardnih elementov podobni gradnji z lego kockami, katerih funkcionalnost določimo z vpisom ustreznega algoritma delovanja. Iniciativa sicer zrcali potrebe in načrte ameriške vojne mornarice, kot je program »more electric ship« in drugi, vendar je njegov cilj mnogo širši: razviti novo filozofijo načrtovanja, razvoja, gradnje, proizvodnje in uporabe naprav močnostne elektronike, kot tudi distribucije električne energije v raznih avtonomnih sistemih. Program sicer še ni sprožil serijske proizvodnje gradnikov, ne vzpostavil novih standardov na področju močnostne elektronike, je pa že prinesel nove elemente kot so MOS krmiljeni tiristorji, nova paradigma v krmiljenju močnostnih stikal, ki vključuje tudi digitalni komunikacijski sistem, pametne senzorje in digitalno obdelavo signalov. 1. Introduction The power building block (PEBB), initiated by Office of Naval Research (ONR), Is promising enabling technology which will promote future electrical power systems. A PEBB is concept of building a larger power processing system from relatively small number of standardized units which have high degree of intelligence and control autonomy, and which are themselves built from smaller standardized units with some, but less intelligence and autonomy, which in turn also can be but by even smaller, elementary blocks and so on /1-4/. Therefore a PEBB is not some specific block, but rather a building block concept. It starts from the smallest block, i.e. smart switches, smart sensors, etc, which are used to build smart power processing units, e.g. inverters, rectifiers, motor drivers, solid-state circuits breakers, etc. These power-processing units are combined to provide more complex function, or a single function but with higher power rating than each individual unit. At any level, a PEBB module has form depicted in Fig. 1. This concept makes difference to classical design of power processing devices in following: thermal disipation I power /)—s^ power input fc^ f \ output informations (communications) Fig. 1: PEBB module interfaces 1. Every, even the simplest module has some Intelligence and includes some communications capability, 2. Physical properties at each of the four interfaces (connectors, screws, surfaces, etc) are standardized for each PEBB power level. Planed are three power ranges: a. Low Power 10 kW to 100 kW b. Medium Power 100 kW to 500 kW c. High Power 500 kW to 10 MW 3. Electrical properties at each interface should be standardized, 4. Compatibility of all modules that connect at the some interface is guaranteed a priory. 94 Z. Cucej: Power Electronic Building Blocks: A Survey Informacije MIDEM 31(2001)2, str. 94-101 The initial intent of the PEBB program was to development or fosters the development of a family of power electronic modules that can be used in 80% of the power conversion and power control applications in the commercial and military world. The technical goals for the PEBB were as follows: 1. Size and packaging, for example, a 250 kW single-phase PEBB module should be fit in a volume roughly the size of a shoebox without the output filter circuits but with built-in provision for thermal management. 2. Power conversion efficiency greater than 98%. 3. Output power quality less than 5% Total Harmonic Distortion (THD). 4. Electromagnetic Interference (EMI) levels belowthose specified in Mil Std 46. It is the objective of the PEBB program to promote innovative development of a family of power electronic devices that satisfy the PEBB goals. Furthermore, this program likes to stimulate and support competing ideas in order to advance the state of the art and produce the best possible PEBB modules /5,6/. Of course, main goal is to have PEBB modules produced in the US by US manufacturers. 2. Topology For electric power conversion a different kind of switching converters are employed. Their switches are implemented by one of three basic switch topologies (Fig. 2), which together with switching control must guarantee the elementary safety operation: no shorted voltage source, no open current source. Analysis of power converters topologies show, that medium and high power converters are built up from different interconnected half-bridges (Fig. 3). Further, the control of switches in half bridge is very tied: if one is in on state, the other one has to be in off state. Fig. 2: Basic switches topologies. From left to right: voltage unidirectional, current unidirectional and bi-directional. 2.1. Impact of soft switching techniques Reduction of thermal dissipation is very important issue in integration of PEBB elements into compact peace of hardware. Meanwhile the contribution of static losses is reducible only by inventing a new semiconductor switches, the switching losses can be reduced also with appropriate modulation techniques as well as with use of soft switching. So far, many soft switching topologies have been proposed to reduce the switching loss and improve the performance of converters. All have been evolved from resonant converters, quasi-resonant converters, multi-resonant converters, soft switching PWM converters including zero-voltage transition (ZVT) and zero-current transition (ZCT). They can be classified be classified into two categories: zero voltage switching (ZVS) and zero-current switching n......; r—■ s—■ t—■ ;vn s Boost Rectifier Buck Rectifier 1 ' M ^ { dc/ H Ï If ¿ST Mm. IN MSk an ¿8» DC/DC Converter Three-Level DC/AC Converter Fig. 3: Identification of a PEBB Switching cell: The commonality in the power converters is presented as the shaded block 95 Informacije MIDEM 31(2001)2, str. 94-101 Z. Cucej: Power Electronic Building Blocks: A Survey (ZCS). ZVS reduces the switch turn-on loss by forcing the switch voltage to zero priorto its current flowing, while ZCS reduces the turn-off loss by forcing the switch current to zero before its collector-emitter voltage Increases from zero to turn-off static value. For medium to high power applications, ZVT and ZCT are more suitable than other soft switching techniques, since they combine the advantages of PWM control (i.e. minimum switch static voltage/current dynamic and minimum circulating energy), and the advantages of soft switching techniques, i.e. low switching loss and low dynamic transition. 2.1.1. ARCP inverter The ARCP (Auxiliary Resonant Commutated Pole) inverter belongs to ZVS family of soft switching inverters /6/. In its topology (Fig. 4), the voltage across each phase switch (5, and S2) is driven to zero just priorto its turn on. This is accomplished by generating a resonant current pulse that drives the voltage across the switch to zero. The resonant pulse is formed when auxiliary switch (AC) consisting from switches A, or A2 is turned on just prior to turning off a phase switch. A detailed description of ARCP operation can be found in reference /7/. Briefly its operation can be described as follows. When the AC switch is gated on, a current begins to rise linearly through the resonant inductor L,{ in the conducting phase switch. When the phase switch is turned off, the current resonates based on the resonant component values and then falls back to zero. The peak resonant current depends on the following (see Fig. 6): +BUS cbus Cbus -BUS axillary switch m main switch »Si Lf |0 * 'HIM.....Q â ! 0, r v„ SH Ai SL A2 or off > t Fig. 4: ARCP schematic and switching timing Length of time that both the AC and the phase switch are turn-on simultaneously (overlap time) Input bus voltage For AC switches in ARCP Inverters the MCT (MOS Controlled Thyristors) have been developed and provided under the ONR PEBB development program. These devices can withstand high dv/dt and di/dt stresses making them ideal candidates for use as AC in the ARCP topology. S2 voltage for 600 V QC bus •200 -300 S2 voltage for 600 V DC bus 100 0 7,649 7,650 7,651 7,652 7,653 time [s] 7,654 Fig. 5: ARCP Resonant Transitions. Efficiency of ARCP inverters strongly depends on resonant pulse control. Minimization of resonant energy required for soft switching can be achieved by introducing of a smart control with self-tuning the overlap time to the actual input DC bus voltage and actual load current. Example of smart control is LMARC (Load Modulated Auxiliary Resonant Current) control algorithm reported in reference /6/. LMARC determines overlap time according to the instantaneous load currents. To insure zero voltage transitions the adequate safety margins, i.e. more resonant energy than what is theoretically needed is maintained. LMARC also considers the facts that the magnitude and direction of the instantaneous load current flowing through a main switch or diode can help or hindrance of resonant transitions. 2.1.2. ZCT converters A ZCT PEBB can be regarded as the combination of two soft switching cells. One of them is shown within the shaded area in Fig. 6. The relationship between the main switch and its corresponding auxiliary switch in one PEBB topology is diagonal. This means the timing control of Au's related to Sh- On the other hand, Ah is related to Sl. The key waveforms and the control timings are shown in Fig. 7, analysis of improved ZCT can be found for example in /8,9/. Let be emphases, that ZCT only help the switching transition, so the power converters with ZCT operates according to PWM rather than switching transition. So the controller design is almost the same as at the hard switching converters. Resonant component values ( LR and CR) 96 Z. Cucej: Power Electronic Building Blocks: A Survey Informacije MIDEM 31(2001)2, str. 94-101 A H OH K V, o LI % OH % v^R OH h v, AC Fig. 6: Topology of one ZCT PEBB power stage for boost rectifier In the beginning to HM belongs pulse-width modulatorand analog-to-digital converters preparing data for AM (Fig. 8). For AM has been proposed cascade controller structure. The concerns of inner loop are electric variables like input/output voltages and currents, the outer loops concern are load variables, for example motor torque and angular velocity. This solution needs numerous noise sensitive signal lines between HM and elements of PEBB. This was eliminated by further development of PEBB concepts where in PEBB control was introduced smart sensors generating data instead of signals and smart gate drivers capable converting digital commands into adequate drive signals. In this concept modulator and AM vas merged into universal controller (Fig. 9), HMandAM communicate over fast serial bus interface (Fig. 10). Fig. 7: Operation waveforms for the improved ZCT 3. Control and communication ¡sues The control of PEBB is divided into two parts: 1. Controller of power stage of PEBB, which was named Hardware Manager (HM), and 2. Controller of PEBB's applications, which was named Application Manager (AM). . POWER : : HARDWARE i ! APPLICATION porter :n STAGE MANAGER MANAGER Power k. Filler S ? Sensors ? ^ 1 us AtoD 6 Conv......ß 10 {Adulator •nm'-mmmeS' ■ -^mommm* Powercpnqnr„f1--1 AtoD 1» Filter M 1 bensorei [ Conv J Ac,jao' "ÜÜÜi__Lî 100 -s . i System >i Level ¡Controller] 10 ms system ANALOG ..action.........SIGNALS.. MIXED SIGNALS DIGITAL . SIGNALS.. Fig. 8: PEBB module interfaces POWER STAGE and ! HARDWARE MANAGER i illliiipSiiiii f Power k f Smart » Filter......Jf-.^Sensoi Jj 1Osr UNIVERSAL CONTROLLER (AM) WITH SERIAL BUS INTERFACES I Abator : 1000s ! 110 ms I Moclulator^ConíÍoíle| ^Comroileij; > < JSus', Power ^ . Smart 6 /l!'f\ \l R,£i_J 'Sensor J ' MIXED SIGNALS DIGITAL SIGNALS FIG. 9: Universal controller with serial bus interfaces Serial communication between HM and AM has specifics not found in existed industrial communication systems. As it is on one hand very simple and mostly performs cyclic traffics, on another hand it had to be very fast, has very low synchronization jitter and should be reliable. master node Universal «SBÍ PEBB Controller data in A/D data out ■■■■■■■ lasQEisas rut tu r.i I I ü BBaasH PEBB (1) PEBB (2) Active Slave Slave Slave node node node Fig. 10: Inter PEBB and UPC communication 4. Interconnections Interconnection of a PEBB's components into compact device is one of a major issue of PEBB initiative. There arise lot of problems because only in rare cases it is possi- 97 Informacije MIDEM 31(2001)2, str. 94-101 Z. Cucej: Power Electronic Building Blocks: A Survey ble to connect one component directly to the adjacent component. The stray inductance and capacitance of the interconnection, which are often impossible to determine in advance, consequently accurately modeling of the converter is not possible. This leads to a lot of unnecessary laboratory experimentation during the interconnect development. Furthermore, components are not mechanically interchangeable, requiring sole sourcing of many components. One of solutions for above problems is proposition for a system called Coordinated Interconnect (CI) /10-11/, which byachange in component terminations philosophy can greatly improve converter design and construction. New philosophy emphases the component terminations should not govern the interconnect design, ratherthe interconnect design should govern the component terminations. Proposed CI eliminates the wiring harness and busses typical of present-day converters. The concept of CI is to integrate a section of laminated bus, or at least a bus-like structure into each component. The bus is terminated with a bus edge connector which mates directly to the bus edge connector of the adjoining component. Consequently all interconnect stray elements are included with the components and are characterized as part of the component data sheets. Therefore modeling of the converter prior to construction is greatly simplified. Furthermore, components of various types are mechanically interchangeable with each other. Finally the concept of CI allows replacement of a single component without disturbing other components or connections. Designing CI the selection of the number of layers is a key decision. Since CI should be carried throughout the converter, both the ac and dc sections of the converter should use CI. In the dc section buses often require a "+" layer, a "-" layer, and a midpoint or "0" layer. Coincidentally, the ac section of a three-phase converter requires three layers for phases a, b, and c. Therefore was proposed a three-layer system, which could easily be reduced to a two-layer or enhanced to four or more layers. As shown in Fig. 11, a vertical tab terminates each of the three horizontal bus layers. Each tab occupies a width W and is isolated from its neighbor by separation S. The bus thickness determines the tabthickness T. The bus thickness depends on com- ponent design and can be different for different components. All tabs must extend above the baseplate by a uniform elevation E. Therefore; the tab height H actually can vary depending on the distance between the bus layers and the baseplate. The contact area between the two tabs is the product of W and H. Three-tab bus edge connector has not centerline axis symmetry. Lack of symmetry introduces in the converter layout certain constraints like orientation in component placing. The symmetry is achievable by five-tab bus edge connector (Fig. 12), but requires five connections between adjacent components. Beside of increased it has a total of 4S separation between tabs compared to a total of 2S separation between tabs for the three-tab design. The additional separation reduces the contact area and could be a limiting factor if S is large. Component 1 Parting (tabs only) Line Layer 1 (top) -Layer 2 (middle) Layer 3 (botom) Layer 2 (middle) -Layer 1 (top) Component 2 (full bus) ÖJ ■CP to - .Line of... Symetry W/2 Fig. 12: Five-tab bus edge connector for three-layer bus. Many different techniques could be used to fasten the tabs to each other. Fig. 13 shows three example methods. Traditional bolt, washers, and nut (Fig. 13a) are not convenient for mounting, more convenient is use of a spring steel clip, which can be inserted from above with minimum clearance on either side (Fig. 13b). Similarly is with the screw-driven wedge (Fig. 13c). By it is possible to connect multiple tabs simultaneously. Those connections can be made and unmade. Permanent connections such as crimping are also easily envisioned. Parting Line; Component 1 j (tabs only) Layer 1 (top) Layer 2 (middle) Layer 3 (botom) Component 2 (full bus) Component 1 (Insulators ^ Layer 1 - •►! / Layer 2 > Layer 3 ► Component 2 ßaSf|iate/Qöoir Component 1 (underneath) I—^ Component 2 Baseplate/Cooler Fig. 11: Three-tab bus edge connector for three-layer bus: (a) top view, (b) edge view with coplanar bus layers, (c) alternate edge view with non-coplanar bus layers and buses of differing thickness. 98 Z. Cucej: Power Electronic Building Blocks: A Survey Informacije MIDEM 31(2001)2, str. 94-101 Bolt Washers Nut Spring Steel Clip Y~\ Screw Driven Wedge I Fig. 13: Methods to fasten tabs of bus edge connector. For wide acceptance of CI sine qua non condition is standardization of CI. At least should be standardized measures E, S, Hmin, W and position of holes in edge connectors. It can be expected that those measurements will be grouped in power classes like PEBB's. Since no currently available components use CI, it would be developed in phases with various components making the transition when possible. Advanced technology components would use CI as an integral part of the component design, for others adapters would be used to make the transition however. Example of it for electrolytic capacitor is illustrated in Fig. 14. + 0 Fig. 14: Three layer bus adapter for electrolytic capacitor. Terminals allow the capacitor to connect to either "+" and "0" layers or "-" and "0" layers. 5. Packaging Issues from a Thermal Perspective Integration of PEBB's components, determined by circuit topology, into compact device depends very much on voltage, current and the amount of waste heat generated. By CI the problems with voltage and currents influence on package is seems to be efficiently solved, but for wasted heat is likely that the common methods of cooling have already reached their limit. To improve performance the waste heat has to be taken out more efficiently. The sketches below outline the various topologies that can be considered for packaging a power electronic switch. Each of the following drawings is laid out in the same basic manner to emphasize the similarities and differences of the topology. Each is shown with a generic heat sink (heat exchanger, fluid link and final heat exchanger). die -conductor -insulator - interface - head spreader fluid link Fig. 15: Conventional heat sink Fig. 3.1 shows a conventional heat sink topology. It is the most common because of its flexibility. With this topology, the worst is the field interface (on the sketch assigned as interface). Even under the best of circumstances it acts as a thermal barrier. Because of material performance limitations and manufacturing techniques the overall package has a lot of layers in the 'stack', each interface providing a thermo-mechanical problem. The attached and integral heat sink topology (Fig. 16) are compromise that has been tried a number of times for both single and double side-cooled packages. At integral heat sink the insulator is part of the mechanical structure and overtake the heat spreader functionality, so minimal thermal path from die to heat exchanger seems to make this a near ideal heat management system. Pool and flow boiling as well as spray and impingement using Fluorocarbons all appear to promise very real performance boosts and would be worth development. Therefore the integral heat sink topology is a basis for the temporary phases of PEBB program. Fig. 16: Attached (left), and integral (right) heat sink. The double side cooled topologies are complex layout (Fig. 17). They have similar properties as one side cooled counterparts, but with important benefits, that in comparison to them have halved thermal resistance. Unfortunately, those topologies require a new way of connecting the package to the outside world. Fundamental changes in package form, power interface and control connection is required. In thermal sense the best possible thermal performance is feasible by integral liquid cooling (Fig. 18) where the heat exchange liquid is right at the die. Further advantage is that the package does not need to use the expensive ceramics and engineered metals used in conventional high performance module designs. The package can be designed as one large heat exchanger operating at a high temperature. It can be cooled efficiently with forced air. However the performance and size advantages seem to outweigh the need to use special liquids. For future high- 99 Informacije MIDEM 31(2001)2, str. 94-101 Z. Cucej: Power Electronic Building Blocks: A Survey silili Fig. 17: Double side cooled packages, a: Hockey puck or press pack, b: conventional, c: attached heat sink), d: integral heat sink. have approximately equal thermal resistances. Each single layer in package has full height; doubted layers are half height since they would approximately halve the thermal resistance. This illustration has a lot of simplifying assumptions but hopefully it shows why the 'advanced' module designs are of such interest. This analysis probably understates the performance gains of the more 'advanced' packaging styles. The pivot in packing development is development of packaging materials. For them are many performance parameters of importance, however the primary areas of interest to the PEBB program are thermal issues relating to coefficients, reliability and performance. For reliability the primary driving force is the mismatch of Thermal Coefficients of Expansion (TCE) between layers in a packaging stack. Thermal Conductivity (TC) measured in W/ mK reflects the thermal performance/power dissipation. A list of packaging electronic materials with their TCE and TC considering in PEBB program is in Table 1. Table 1: Electronic materials power-density PEBB's this certainly seems to be a promising approach. fluid link Fig. 18: Integral liquid cooling Chart in Fig. 19 shows an analysis of efficiency of different cooling systems. In analysis it is assumed that all layers U heat exchanger liquid media . heat exchanger ~ interface " „ heat spreader □ insulator conductor die Imersion Cooled Hockey Pack Double side integra Integral Double side attached Attached Double side cooled conventional Conventional TCE TC [W/mK] Type Thermal grease - 1 I Diamond 1 >2300 I Si3N4 2 270 I BN 4 600 I CuGrpht MMC ~4 -250 C AIN 4 180 I Si 4 160 S SiC 4 270 S/l CuMoCu 7 200 C Al203 7 23 I BeO 8 240 I Cu 18 395 C Al 24 205 C Circuit Board 130 0,24 I AlSiC 180 180 C Solder (Sn/Pb) 210 36 C/A Thermal Epoxies <700 1 l/A Fig. 19: Comparative Thermal Resistance Type codes: I - Insulator, C: Conductor; S - Semiconductor, A - Attach All numbers are approximate Conductors have to be directly bonded to the die at least on one face. Electrical conductivity is a prime parameter but because of the close proximity to the die, their TCE needs to be as closely matched as possible. Electrical insulators are relatively good thermal conductors, but the less expensive ones are generally poor performers in this area. Most ceramics insulators have relatively small TCE's while organics have high TCE's. The cheap organic insulators can be inexpensively formed into complex shapes while 100 Z. Cucej: Power Electronic Building Blocks: A Survey Informacije MIDEM 31(2001)2, str. 94-101 the ceramics are all expensive to form into anything beside flat plates. Attachment materials are solders and organics. The most common solders are tin/lead alloys and although other mixtures are used fairly frequently, they have somewhat similar characteristics. Organic attachment materials are electrical and thermal insulators; though they can be 'loaded' with other materials that can modify either or both the electrical and thermal properties. Organics can be made to adhere to just about any surface and are generally processed at low temperatures that give them a great deal of process flexibility. Heat spreaders are the relatively thick, flat base-plates of power modules that provide a stable base on which the components are mounted in conventional modules. They are generally made of copper, provide a good path for heat dissipation, and form a "thermal capacitor" to absorb heat spikes and protect the device when a short-term overload situation occurs. Heat sink/heat exchangers are usually just extruded or machined aluminum. The term heat exchanger is generally used for active devices where hot a low temperature and usually different fluid flowing on the other side cool flowing fluid on one side of an interface. Most heat exchangers are made of aluminum. 6. Conclusions This paper demonstrates the progression in development of PEBB concept and philosophy. From past research and development can be concluded that PEBB will not have unique topology. Regard to application the hard switch and ZVT or ZVT soft switch versions will be available. The control of power electronics in future will be split into part integrated into PEBB, which in collaboration with smart sensors and gate drivers will control PEBB behavior and will be through fast serial digital communication linked with application control. This communication will have the same importance as have l2C in connections of chips. The power electronics would benefit enormously if the industry of elements used in power electronics will accept system of Coordinated Interconnect just as the computer and other digital industries benefited from the dual inline package (DIP) and subsequent surface mount devices. But that this will happen many important challenges must be met. Thermal aspects of PEBB's packaging give insight in problems of integrating PEBB into compact device. From brief overview of packing technologies can be concluded, that Integral heat sink technology is basis of temporary phases of PEBB program. In future, when high temperature devices like SiC elements will be available at reasonable cost, it seems that integral liquid cooling will prevail. For this cooling a long way of searching for materials with appropriate TCE is still to be passed. 7. References /1/ D. Boroyevich: Some control, communications, and modeling Issues for PEBB based power distribution systems. White paper as part of the Control and intelligence systems control of ONR PEBB control technology workshop, 1995 /2/ K. Drew, "PEBB technology development and cost assessments benchmark as of October 9, 1998, ONR, code 36 (http:// pebb.onr.navv.mil) /3/ G. S. Thaudi: Modeling, control and stability analysis of a PEBB based DC distribution power system. M.Sc. thesis, VPI&SU Blacksburg, Va., 1997 /4/ T. Ericson, A. Tucker, D. Hamilton, G. Campisi, C. Whitcomb, J. Borraccini, W. Jacobsen: Standardized power switch system modules (power Electronics Building Blocks). Power systems world '97, 1997 (http://pebb.onr.navv.mil) /5/ J. Borraccini, W. Ruby, T. Duong, D. Cochran, E. Roth, D. McLaughlin, T. Ericsen: Demonstration of Power Electronic Building Block (PEBB1) Function, and Plans for PEBB2 and PEBB3. Report (http://pebb.onr.naw.mil). /6/ W. Ruby, R. Cooley, J. Borraccini, M. Cannell, J. Sullivan, J. Baker, R. Sigethy, G. McKibben: Power Electronic Building Block design and hardware demonstrator - results from December 1996 through May 1998. (http://pebb.onr.naw.mil) /7/ R. W. DeDonker: "Resonant Pole Converters". EPE-93, Ch. 4, p 4-1 through 4-44, 1993 /8/ J. Mayer: Analysis of Zero-Current Switching Topologies and Strategies for the Power Electronic Building Block. Final Technical Report for Naval Surface Warfare Center, February 1998 /9/ A. W. Kelley, M. Harris, D. Hartzell, and D. Darcy, "Coordi-nated Interconnect: A Philosophical Change in the Design and Construction of Power Electronic Converters, 33rd IAS Annual Meeting, 1998, St. Louis, Missouri, USA, pp. 1105-1110. /10/ A. Kelley, M. Harris, J. Cavaroc, M. Jones, R. Linkous, D. Hartzell, D. Darcy: "Bus connector for coordinated interconnect laboratory measurement and finite element simulation" APEC, Dallas, Texas, 1999, pp. 325-331. /11 / W. A. Stinnett: Thermal management of power electronic building blocks. M.Sc, thesis, VPI&SU Blacksburg, Va., USA, 1999. /12/ J. Borraccini, W. Ruby, R. Cooly, M. Cannel: Calculation of power density of PEBB 1.5 based ARCP electrical power converter. 1998 (http://pebb.onr.naw.mil). /13/ P. N. Harrison, R. W. Garman, "PEBB Thermal Baseline Study Test Plan," A&T Engineering Technologies, VECTOR Research Division (July 8, 1998). /14/ P. N. Harrison, R. W. Garman, "PEBB Thermal Management Final Report," A&T Engineering Technologies, VECTOR Research Division (May 1999). /15/ JiaWu, Heping Dai, KungXing, FredC. Lee and Dushan Boroyevich: Implementation of a ZCT soft switching technique in a 100 kW PEBB based Three-phase PFC rectifier, IEEE conference PESC'99, reprinted in 1999 Annual Power electronic seminar, Virginia Tech, Blacksburg, USA Žarko ČUČEJ Univerza v Mariboru Fakulteta za elektrotehniko, računalništvo in informatiko Smetanova 17, 2000 Maribor-SI e-mail: žarko.cucej@uni-mb.si Prispelo (Arrived): 24.03.01 Sprejeto (Accepted): 01.06.01 101 Informacije MIDEM 31 (2001 )2, Ljubljana UDK621,3:(53+54+621 +66), ISSN0352-9045 A STUDY OF THE LIMITS OF SPIN-ON-GLASS PLANARIZATION PROCESS R. Osredkar Faculty of Computer Sciences and Faculty of Electrical Eng., University of Ljubljana, Slovenia Keywords: semiconductors, microelectronics, IC, Integrated Circuits, topography planarizatlon, SOG films, Spin-On Glass FILMS, production, process modeling, PECVD, Plasma-Enhanced Chemical Vapour Depositions Abstract: Results presented in this paper demonstrate that global planarization with a SOG planarization process can not be achieved. However, local planarization on a predetermined site on a patterned wafer is possible, with a planarization factors of 0.81 for a single step process, 0.86 for a double step process, and 0.90 for a triple step process. Such planarization involves repeating the deposition and denslficatlon steps of the SOG material several times, and can be accurately modeled by a simple model described. Študija omejitev planarizacijske tehnike s tanko plastjo tekočega stekla (SOG) Ključne besede: polprevodniki, mikroelektronika, IC vezja integrirana, planarizacija topografije, SOG plasti tanke stekla tekočega nanesenega centrifugalno, proizvodnja, modeliranje procesov, PECVD nanosi kemični s paro plazemsko Izboljšani Povzetek: Rezultati predstavljenih meritev kažejo, da je globalna planarizacija topografije na silicijevi rezini izven dosega metode planarizacije s tanko plastjo tekočega stekla (SOG). Vendar pa se z metodo, na določenem mestu na rezini, da doseči lokalno planarizacijo, s planarizacijskimi faktoji 0.81 za enostopenjski proces, 0.86 za dvostopenjskega in 0.90 zatristopenjskega. Takšen večstopenjski planarizacijski postopek zahteva večkratno, zaporedno nanašanje In utrjevanje SOG planarizacijskega materiala in ga je možno natančno opisati s preprostim modelom planarizacije, ki je tudi opisan. Introduction Device planarization, i.e. reduction of distances between topography and reduction of the side wall slopes in order to facilitate subsequent processing steps, is an important consideration in IC fabrication technologies where circuit features are scaled to submicron dimensions. It is most critical during the final steps of fabrication, when several metallization and dielectric layers are deposited, and is used primarily to enhance step coverage of these layers. Often only partial planarization (smoothing of topography), with limited step heights reduction is sought /1,2/. However, sometimes complete local planarization is required, and even complete global planarization, where the surface of the wafer is completely planarized over arbitrary topography. The latter requirement arises e.g. in LCD technologies where the globally planarized wafer surface is the lower electrode of a LC display /3/ or In ferroelectric memory devices /4/. There are several planarization techniques used in IC processing /5/. Physical methods include polishing, which is usually applied where complete and global planarization is required, and different techniques where planarization of existing dielectric layers is attempted by film reflow, etch--back of sacrificial layers etc. Fluidic planarization techniques utilize low viscosity of certain materials, e.g. photoresists, polyimides and spin on glasses (SOG), which can fill the trenches in wafer topography. These methods are simple to apply and usually require low processing temperatures (below 400 °C). However, compatibility of the fluidic materials with the standard dielectric materials is a serious concern, and, as a rule, only limited planarization can be achieved by such methods. In this contribution the limits of the SOG planarization methods are studied and described. Experimental Planarizing characteristics of the Allied Chemicals Accu-glass series 204 SOG material were studied. SOG films were deposited on 4" wafers on a Semiconductor Systems Inc. System One modular coater with an on-line drying oven, at 3000 r.p.m. and the deposited film dried at 100 °C for 60 sec. Resulting film was 315 nm thick, with betterthan 1 % (± 1a) wafer to wafer repeatability in uniformity. Densifi-cations were performed in a Blue M, model IGF 206B-3 furnace, in a nitrogen atmosphere. ASemixTazmo model TR 6132U (D) coater, with 3 ovens, was also used at later stages of the work, eliminating the need of a separate oven for low temperature (305 °C) densification. High temperature densification (900 °C) was performed in the Blue M oven in all cases. The results of planarization processing were photographed on a Hitachi model 405 scanning electron microscope and photographs analyzed. 102 R.Osredkar: A Study of The Limits of Spin-on-glass Planarization Process Informacije MIDEM 31(2001)2, str. 102-105 The patterned wafer topography was simulated by a pattern of 10 parallel aluminum lines on field oxide. The lines were 2.5 (xm wide, 0.35 |im thick (i.e. step heights 0.35 ¡im) spaced 1.5 jim apart (i.e. at 4.0 jim pitch), 3 |im, 4.5 |i.m, 6 |im, and 7.5 |im apart. All planarization factor data presented are an average of 5 measurements on 5 different wafers, with 2 % (± 1 o). Results and discussion Rapid evaporation of the solvent from the SOG material during the deposition process challenges detailed analysis and prediction of the degree of planarization possible with such a process. A quantitative measure of the step-height reduction, referred to as the planarization factor p, is given by (3=1- (tfstep/t'step) (1) where t'step and t'step are the final and the initial step heights, respectively. In complete planarization (3 = 1 and 0 if no planarization exists. The rheological (fludic) deposition model, which is often used in analysis of the spin-on processes and is based on the Navier—Stokes equations /5/, suggests that covering a patterned wafer with a fluid film (SOG, photoresist or poly-imide) results in a completely flat top surface of the film, which remains flat until a considerable amount of solvent is removed from the material. After the removal of the solvent only non-volatile components of the film material remain on the wafer surface. If the proportion of the non-volatile components in the SOG material is k, the planarization factor achieved during the evaporation of the solvents is simply |3 = k, regardless of the thickness of the deposited planarizing film and the resulting partially planarized wafer topography still reflects the underlying topography. In case of Accuglass 204 SOG material, which contains 10 % of nonvolatile components (as specified by the producer), a maximal planarization factor of (3id = 0.1 could thus be expected, as a result of drying of the material. However, this would only be true if during evaporation of the solvents no gross transport of the planarizing material, driven by the surface tension, occurred. This is clearly not the case: in dense topography we have been able to achieve (3 as high as 0.83 (depending on the details of the wafer topography), and less than 0.1 on isolated lines or lines separated by more than 4 to 5 |xm. This indicates that the transport of the planarizing material during evaporation of the solvents plays an important role in the SOG planarization process. The quality of the surface underlying the planarization film also effects the planarization process and is also not predicted by the rheological model. A SOG film deposited on a bare, flat silicon wafer is not uniform across the wafer: it is generally 1.2 % thicker on the wafer center than on its edge. The situation is reversed on films deposited on wafers covered with a 1.3 |im thick PECVD oxide film, which also has a flat surface: in this case the SOG film is 2.7 % thinner in the center of the wafer. Also, at identical coating conditions, average thickness is 3,5 % less than on the bare wafers. SOG films deposited on patterned wafers (patterned aluminum on field oxide) simultaneously exhibit surface and topography effects: their thickness similar to those on PECVD oxide, with a 8.8 % reduction of thickness in the center. These effects are quite reproducible and are several times larger than the pertaining standard deviations of the film thickness as measured at standard positions on the wafers /6/. We conclude that both the surface quality and its structure have important influence on the local thickness of the deposited SOG films, precluding total global planarization with such a process. However, locally the topography effects prevail, which makes partial, local planarization possible. Another difficulty in analyzing in detail the SOG planarization process arises from the rapid drying (evaporation of the solvents) and the associated thinning of the SOG film at 100 °C, the recommended temperature for this stage of processing. No further thinning due to evaporation of the solvents can be observed after only 60 sec, which makes it difficult to measure the original film thickness, unless depositions and thickness measurements are performed in an atmosphere saturated by the solvents. Such measurements have been attempted with inconclusive results: they suggest an as-deposited film thickness of 4jim, which can be compared to 5.6 jim, the result of a calculation based on the rheological model, material and the deposition parameters. As a consequence of the high volatility of the solvent system used the SOG material, the amount of solvent evaporating during the spinning and the formation of the film is considerable, thereby rapidly and locally changing the surface tension and viscosity of the spun-on material. The surface diffusion model of the planarization process, which is often used to model planarization by reflow of doped glass and is conveniently accessible in different simulation packages (e.g. SAMPLE), is therefore unsuitable for simulations of the SOG planarization process. Detailed modeling of the planarizing properties of the liquid SOG material is therefore difficult and only semi-empirical attempts in this direction have been published /7/. After initial drying the behavior of the SOG film becomes well predictable /6/. During densification at 305 °C initially some further expulsion of the solvents from the pores of the film is observed, resulting in thinning of the film in an exponential manner, with a characteristic time of 0.50 hours. After this initial thinning, densification proper of the film can be observed; it also follows an exponential curve, with characteristic time of 1.3 hours. After 3.5 hours of baking at 305 °C the SOG film thickness does not decrease further appreciably. The quality of the deposited film is determined exclusively by the second stage of the densification and results in a porous film. Further heat treatment at a higher temperature reduces the porosity /8/, however if the planarization is applied at a stage where a 103 Informacije MIDEM 31(2001)2, str. 102-105 R.Osredkar: A Study of The Limits of Spin-on-glass Planarization Process metal (aluminum) film is present on the wafer, the possibility of densification at elevated temperatures is strictly limited. Densification at 900 °C removes all traces of silanols and H2O from the film, as has been demonstrated by IR spectroscopy/9/, but still does not eliminate porosity completely. This is illustrated by our rehydration experiments in which freshly denslfied films at this temperature were exposed to an atmosphere saturated with water and from which the films can reversibly adsorb H2O. The degree of water adsorption has been monitored by measurements of the dielectric constant of the SOG film, which ranges from 4.6inadryfilmdensifiedat900°C to 8.3 in a rehydrated film. These results closely correspond to those reported previously /10/ and indicate that moisture content (and possibly silanol content) in SOG films can be, due to possible reactions of the moisture from the film with the aluminum, potentially a serious source of quality degradation problems /11/. In modeling of the planarization factor of the two stage densification process at 305 °C, the initial thinning due to expulsion of the solvents from the film can be, without appreciable loss of accuracy, neglected, and only the characteristic thinning time of the second stage considered. This is due to the relatively small change in the film thickness during the initial stage and the long densification times of the second one. The planarization factor for the densification step only, at specified temperature, is (3d = 0.90. Thus the compound planarization factor for the initial drying and densification is (3 = (3id (3d and depends strongly, as described above, on the topography: it is 0.09 for isolated lines and 0.81 in case of 0.35 Jim step heights of 2.5 jxm wide lines with 4.0 Jim pitch. Attempts at panarization with 2 subsequent SOG depositions revealed that a SOG film dried at 100 °C is readily attacked by the solvents in the SOG material itself and is partially removed during the second deposition. This is demonstrated by the compound thickness after drying which increases by only 50 %, and a resulting (3id , which is, in case of isolated lines, not significantly different than that of one deposition only. The influence of the substrate topography on the double film planarization factor is even greater than in single film case, probably due to the fact, that the material in the trenches between the lines is less accessible to the solvent than the more exposed material. However, no regularity in the planarization factors could be observed for such a process and we therefore conclude that this is not a viable planarization procedure. Deposition of a second film after densification of the first one (at 305 °C) resulted in doubling of the compound film thickness and an increase in the planarization factor (3 from 0.81 to 0.86, an increase of 6.2 %. This increase can be modeled by replacing k, the proportion of the non-volatile components in the SOG material, in the expression for (3, by a related empirical parameter f. This characterizes the dynamic drying-out and densification processes by their end results, I.e. the thinning of the planarizing film at a particular site on the wafer, and thus takes account of all the effects governing the film thinning process at the site, f has to be determined experimentally. If the ratio of the f parameters, describing the reduction of the deposited SOG film thickness under and on a step of initial thickness t'step , is taken to be proportional to the step heights: r = funder/fon = 3 ■ t'step + 1 where a depends on the details of the topography to be planarized, the resulting planartization factor of a multiple-step planarization process can be predicted for a predetermined site on the wafer. In case of parallel lines of the above mentioned dimensions, and for the Accuglass 204 SOG material, a = 7.1 and the model predicts a planarization factor (3 = 0.86 for a double deposition of the SOG planarization material, and 0.90 foratriple deposition. Both values agree well with our experimental data. Reasults are summarized in Table 1. However, such an empirical model can only be used for determining (3 on a predetermined site on the wafer, with specified topography. It is of little value for estimating the degree of global panarization across the wafer. Further, multiple-step planarization is a process of diminishing returns and total planarization, even locally at a predetermined site, may not be a realistic goal of such a multi-step process. Conclusion A detailed understanding of the planarization process is required to design a planarization process which results in the required degree of planarization of a production wafer. Our results demonstrate that global planarization with a SOG process is extremely difficult, if not impossible, to achieve, but local planarization with a planarization factor of 0.9 is certainly within its reach. Such a process involves repeating the deposition and densification steps of the SOG material several times, and can be, for a predetermined site on a patterned wafer, quite accurately modeled by the simple model described. Acknowledgements The use of IMP (San Jose, Ca., USA) facilities for some of the experimental work is gratefully acknowledged. The study has been supported by a grant from the Ministry of Science and Technology of the Republic of Slovenia. 104 R.Osredkar: A Study of The Limits of Spin-on-glass Planarization Process Informacije MIDEM 31(2001)2, str. 102-105 Table 1. Planarization factors after different stages of SOG planarization process Planarization stage planarization factor deposition (including evaporation of solvents at 100 °C, pj: isolated lines 0.09 deposition (including evaporation of solvents at 100 °C, (3J: dense topography 0.9 double deposition with no densification: isolated lines ~ 0.1 double deposition with no densification: dense topography ~ 0.8, not repeatable densification (pd) 0.9 compound (|3id . (3d): dense topography 0.81 double planarization: dense topography 0.86 triple planarization: dense topography 0.90 References /1/ S. Wolf, Silicon Processing for the VLSI Era, Vol. 2 - Process integration, Lattice Press, Sunset Beach, Ca. USA, 1990, p. 191 /2/ P. B.Johnson and P. Sethna, Semiconductor Int., Oct. 1997, p. 80 /3/ J. Pirs, US, private communication, 2000 /4/ Suk-Kyoung Hongetal., Intermetal Dielectric Process Using SOG for Ferroelectric Memory Devices having SrBi2Ta20g Capacitors, J. Mater. Res., Vol. 12, No. 1, 1997 /5/ B. Gspan, Ph.D. Thesis, Faculty of Electrical Eng., University of Ljubljana, 1995 /6/ R. Osredkar, Spin-on-Glass Material Curing and Etching, Micre- lectron. Reliab., Vol. 34, No. 7, 1994, p. 1265 /7/ L. K. White, Approximating Spun-on, Thin Film Planarization Properties on Complex Topography, J. Electrochem Soc. Solid State Science and Technology, Vol. 132, No. 2, 1985, p. 169 /8/ J. D. Romero et al., Outgasing Behavior of SOG, J. Mater. Res., Vol. 11, No. 9, 1996, p.1996 /9/ S. K. Gupta, Spin-on-glass for Dielectric Planarization, Microe-lectron. Manuf. Test., Vol. 12, No. 5, p. 10, April 1989 /10/ S. K. Gupta and R. L. Chin, ACS Symp. Ser., 295, 1986, p. 349 /11/ R. Osredkar, SOG Planarization of Device Topography, MIDEM, No. 3, 1995, p. 107 Radko Osredkar FRI in FE Univerze v Ljubljani Tržaška 25 SI 1000, Ljubljana Slovenia e-mail: radko. osredkar@fri. uni-li. si Prispelo (arrived): 24.05.01 Sprejeto (Accepted): 01.06.01 105 Informacije MIDEM 31 (2001 )2, Ljubljana UDK621,3:(53+54+621 +66), ISSN0352-9045 ELECTRONIC BRACE FOR THE MEASUREMENTS AND ELICITING OF MUSCLE CONTRACTIONS IN A DOG'S ANKLE Matjaž Bunc and 1 Janez Rozman School of Medicine, Institute of Pathophysiology, 11TIS d. o. o. Centre for Implantable Technology and Sensors, Ljubljana, Republic of Slovenia Keywords: medicine, physiology, physiologic measurements, dogs, electronic braces, ankle rotation, muscle contraction, spontaneous muscle contraction, stimulated muscle contraction, isometric muscle contraction, isotonic muscle contraction Abstract: An experimental electronic brace, which is able to evaluate torque in the ankle joint of a dog elicited by spontaneous or stimulated muscle contraction, has been developed. The brace Is also able to impose electrically controlled passive movements on the dog leg. Precise-passive movements, as passive external, electrically-controlled flexion or extension of the ankle of a dog leg, are defined in as speed and angle of rotation/movement. On the other hand, switching in a certain working mode, the brace, equipped with force transducers and a goniometer, could serve for measurements of isometric (locked mode) or isotonic contractions (active mode and passive mode) of a dog leg. A range of the rotation around the ankle joint is limited between -40 and +55 degrees according to the neutral position. The calculated endurance moment of the brace is 2.41x1 CT4 kg m2s"1, while the speed of electronically controlled movement of the brace in the passive mode is up to 78 degrees/second, respectively. In the active mode the brace is able to rotate synchronously with the dog ankle joint with a speed of up to 400 degrees/second. The maximum frequency, on activation of the tibialis anterior muscle current, when the amplitude of flexion was 50 degrees, was 7/mln. In the locked mode the brace is able to measure the amplitude of force of a dog leg isometric contraction elicited by electrical stimulation. The force transducer with a natural frequency of 8 Hz and compliance of 0.4 |.im/g represents a very linear dependence of the output voltage upon the load with a transducer sensibility of 0,5 mV/mN at a bridge excitation voltage of 5V. The nominal range of each transducer is 0-70 N. Elektronska opornica za pasivno gibanje pasje noge in meritev kontrakcije v pasjem kolenskem sklepu Ključne besede: medicina, fiziologija, merjenja fiziološka, psi, opornice elektronske, rotacija gležnja, krčenje mišic, krčenje mišic spontano,krčenje mišic stimulirano, krčenje mišic izometrično, krčenje mišic izotonično Povzetek: Izdelali smo elektronsko opornico za pasjo nogo, s katere je moč meriti momente v pasjem gležnju, ki ji izzovejo mišice ob spontanem ali stimuliranem krčenju. Poleg tega je mogoče z opornico izzvati v naprej predvidene pasivne gibe pasje noge z natančno določeno hitrostjo krčenja ali raztegovanja in kotom premika opornice ter s tem na njo pritrjene pasje okončine. Razen tega lahko opornico priredimo za meritve izometrične kontrakcije (locked mode) ali pa izotonične kontrakcije (active mode) ter za prej omenjena programirana gibanja opornice (passive mode). Kot za katerega se lahko zavrti opornica opornice glede na nevtralno lego, določeno z nevtralno lego pasjega gležnja, je od -40 do 55 stopinj. Izračunani vztrajnostni moment opornice je 2.41x10"4 kg m2s"'. Pri pasivnem, programiranem gibanju opornice je moč nastaviti hitrost rotacije v območju od nekaj stopinj/sek do največ 78 stopinj/sek. V aktivnem načinu pa se opornica lahko zavrti, skupaj z stimulirano pasjo nogo, s hitrostjo tudi do 400 stopinj/sek. Največja frekvenca draženja mišice tibialis anterior, pri kateri je bilo moč izvajati meritve v aktivnem načinu brez popačenja (amplitudi zasuka opornice 50 stopinj) je bila 7/min. Na opornico je bil vgrajen tudi senzor sile, katerega resonančna frekvenca je bila 8Hz, podajnost (compliance) 0.4 um/g in občutljivos 0.5 mV/mN (napajanje 5V). Občutljivost je bila pri napajanju s 5V v pričakovanem področju merjenih sil (0-70 N), povsem linearna. Introduction In physiological studies of muscle contraction and contemporary nerve activity it is suitable to have special equipment for eliciting controlled mechanical contractions of different muscles. The aim of this work was to develop a mechanical system that would be able either to measure or to impose movements of a dog ankle. Therefore, the aim of our work was to develop a special electronic brace forthe dog leg. The brace should be able to elicit precisely defined (angle and speed) passive movements of a dog leg. On the other hand, the characteristics of both, isometric and isotonic contractions of a dog ankle muscle, caused by electrical stimulation, should be measured. Materials and Methods The brace The brace consists of a mechanical joint that could be attached to the ankle of a dog. Such a fixed mechanical joint (ankle) turns around together with the ankle of a dog continuously. The artificial mechanical joint is a construction of one fixed part, artificial ankle and a rotate-able fine bearing, which, fixed on a dog leg, forms common axes with the joint of a dog (Fig. 1). The joint Is connected to the actuator by mechanical transmission with a hysteresis angle of ±0.5 degree. The system measures the angle of rotation and the torque Induced by the ankle of the dog either due to electrically powered passive rotation of the mechanical joint or electrical stimulation of the dog muscles. The rotate-able artificial ankle has the function of a force transducer at the same time. The brace is construct- 106 M.Bunc, J.Rozman: Electronic Brace for the Measurements and Eliciting of Muscle Informacije MIDEM 31(2001)2, str. 106-109 ed in such a way that it could be used for experiments either on the left or on the right leg. It just has to be turned around on the white or black plate (see Fig. 1). tions divided by angles of rotation and is equal to 2.66:1. The mechanical transmission was selected on the basis of the specified requirements of acceleration and velocity in A ni ech an o-electric transducer B DC motor/gear C goniometer Fig 1. The brace. The bear brace is shown on the left of the picture, the positioning of the dog leg into the brace is shown on the right. A) position of force transducer, B) DC motor/gear, C) goniometer. Description of the sensors Mechano-electric transducer The force transducers were made up of a full Wheatstone bridge composed of four semi-conductor strain gauges /1 / bonded on the artificial ankle (Fig.1.). The voltage signal, produced by a deformation of the semi-conductor strain gauges, is amplified by a precision strain gauge amplifier (Linear Technology, LT 1101). Sensor of angle rotation - a custom designed goniometer In order to measure and control an angle In the joint a custom designed goniometer manufactured from a precision potentiometer with a resolution of 0.1 degree {ITIS d.o.o., Ljubljana) is mounted at common axes with the rotate-able artificial ankle (Fig. 1). Mechanical part of the brace Passive movements of a dog ankle are elicited electrically by powered motor movements of the artificial ankle brace transmission (Fig. 1). Actuator system The complete actuator system is mounted on an aluminum plate, the base of the brace. It is possible to regulate the motor speed and number of revolutions by the PC controller. The ratio of transmission is defined by motor revolu- the passive mode with respect to the friction of transmission. The chosen system comprises a direct current (DC) motor within grounded iron cage to minimize electromagnetic artifacts. Motor control An actuator system involving the aforementioned DC motor/gear system (Fig.1) is mechanically connected to the mechanical joint, and joint thus transferring the torque to the dog joint. By position feedback obtained through measuring an angle in the mechanical joint, the motor is regulated in such a way that it rotates at a chosen speed for any angle according to the neutral position of the ankle. The mechanical system is able to operate in three modes: passive, locked and active mode. In the passive mode the brace is able to rotate the ankle by a predefined angle at a different predefined speed. Therefore, In this mode a rotation from the actuator is transferred to the ankle joint, thus imposing a stretch of a dog ankle extensors or flexors. The common friction, expressed as the certain amount of torque In the passive mode, is composed of friction of the potentiometer, four fine bearings and the transmission. In the locked mode, the position of the motor and artificial ankle is locked at a desired angle in order to measure the isometric torque elicited by electrical stimulation of the muscles or muscle group under investigation. The force transducers, described above, measure the torque of contrac- 107 M.Bunc, J.Rozman: Informacije MIDEM 31(2001)2, str. 106-109 Electronic Brace for the Measurements and Eliciting of Muscle ... tion through deformation of the sensors. In order to achieve a dynamic range of measurement in the active mode, the system is able to follow the ankle joint rotation with fast cadence elicited by electrical stimulation of a nerve or muscle. Measurements of passive and dynamic characteristics of the brace Passive characteristics of the brace The maximum speed of the ankle movement was determined by goniometric measurement of an angle speed of the spare brace rotation at the highest DC motor performance. Brace friction The common friction of the brace was defined by feeding a known DC to the motor and measuring the mechanical energy output. The difference of the input and output energies reveals the friction of the system. Dynamic characteristic of the brace The dog muscle contraction was elicited by electrical stimulation of the sciatic nerve using stimuli with frequencies ranging from 0 to 20 min"1. Since contractions of the leg were detected by the brace, we could determine the frequencies where the response of the brace is linear. This means that the ratio of stimulus/contraction detected without artifacts due to the brace friction or endurance is 1. Endurance moment of the artificial ankle The endurance moment of the brace was calculated considering the dimensions (14 x 3.3x 1 cm), shape and material (aluminium) of the artificial ankle. Selective stimulation of fibers in the sciatic nerve of a dog with a 33-electrode stimulating and recording spiral cuff The cuff was made by bonding two 0.1 mm thick silicone sheets together /2-5/. One sheet stretched and fixed in that position was covered by a layer of adhesive material (NuSil, MED-1511). A second unstretched one was placed on the adhesive and the composite was compressed to a thickness of 0.3 mm. When released, the composite curled into a spiral tube as the stretched sheet contracted to its natural length. 33 electrodes (0.6 x 1.5) mm made of 0.05 mm thick platinum ribbon connected to lead wires were mounted on the third silicone sheet. They were arranged in three parallel spiral groups each containing 11 electrodes at a distance of 0.5 mm. The distance between the spiral groups was 6 mm. Electrodes of the central group were connected to lead wires individually, while the corresponding outer electrodes were shunted to each other and then connected to lead wires. The silicone sheet with electrodes was bonded on the inner side of the cuff. The cuff with an inner diameter of 2.5 mm was trimmed to a length of 20 mm. The lead wires were connected to the connector to be implanted within the lateral subcutaneous tissue for the time between stimulation. Rectangular, bi-phasic, charge balanced, current pulses with a frequency of 20 Hz and amplitude of up to 1 mA were delivered on the central electrode of each GTE within the cuff. As a neutral electrode a hypodermic needle was inserted in the subcutaneous tissue of the thigh, slightly proximal to the cuff. Selective recording of electro-neurogram (ENG) from the sciatic nerve of a dog The cuff already described above was used also for the selective recording of the ENG from a dog nerve after passive or active dog leg movements. ENGs are recorded differentially and selectively with the spiral cuff (see above) from two superficial regions of the sciatic nerve innervating mostly the aforementioned muscles /6-7/. Since the motor system has to operate simultaneously with noise-sensitive ENG measurements, the electromagnetic noise of the motor system was reduced by using a RFI filter and ferrite cores on the supply connections. Shielded wires and the motor and proper ground connection were implemented throughout the entire electrical circuit. Results 100 0 1,.V I degrees Í20ms! jneurt gran ¡rotation a¿gle Fig 2. Detection of the contraction of the dog ankle in the passive mode of the brace. The upper trace shows a neurogram recorded from the sciatic nerve after rotation of the brace and the dog leg with a DC motor system at 50 degrees. In the passive mode (Fig. 2) the brace is able to rotate to a maximum extension of 45 degrees and of maximum flexion of 55 degrees, according to the neutral position of the ankle. The DC motor/gear system is able to perform movement of the artificial ankle with a speed of up to 78 degrees/second. However, practically we could not exceed 7 passive movements with maximum amplitude of flexion and extension of a dog ankle per minute during the experiments because of the combination of endurance and fric- 108 M.Bunc, J.Rozman: Electronic Brace for the Measurements and Eliciting of Muscle Informacije MIDEM 31(2001)2, str. 106-109 tion of the complete system and resistance of the dog ankle. The friction of the system presents less than 2% of the input electric force. In the active mode the brace is able to measure reliably the parameters of a dog ankle contraction elicited by the electrical stimulation of a nerve. In or-derto follow the ankle joint without resisting the movement, the brace is able to perform an ankle rotation of up to 400 degrees/second synchronously with a dog ankle. The calculated endurance moment of the brace is 2.41x10"4 kg m2 s~1. The maximum frequency at which the ratio stimulation/contraction is lower than 1 depends on the amplitude of the brace movement due to the dog's leg contraction. In our experiment, at an amplitude of 50 degree of flexion and sciatic nerve stimulation current of 1.4 mA, the maximal frequency of stimulation was 10/min. Above this, we could not measure the contraction parameters of a dog ankle at the maximum amplitude of flexion and extension without artifact any more. electrical neuro-stimulus Fig 3. Detection of the force of contraction of the dog ankle in the locked mode of the brace. The upper trace shows the neuro-stimulus applied to the sciatic nerve. The lower trace shows force of the dog leg developed after nerve stimulation. In the locked mode (Fig. 3) the brace is able to measure the amplitude of force of the dog ankle contraction elicited by electrical stimulation. The transducers with a natural frequency of 8 Hz and compliance of 0.4 |-im/g represent a very linear dependence of the output voltage upon the load with the sensibility of transducers being 0.5 mV/mN at a bridge excitation voltage of 5V, The nominal range of each transducer is 0-70 N. Discussion According to the aims of the brace construction determined in the introduction, we can conclude that all of the aforementioned requirements were met. The brace is a suitable tool for the study of contractions of different muscles or muscle groups of a dog leg as a result of selective stimulation of a peripheral nerve. On the other hand, nerve activity from a peripheral nerve, describing the torque and angle of rotation in the ankle joint as a consequence of flexion or extension elicited by the brace or by passive move- ments of the leg, could be recorded. The limitation of the transducer is that it has a relatively high endurance that could not be easily diminished. It enables recordings of muscle contraction parameters at higher frequencies of nerve stimulation. On the other hand, the brace, due to its low friction, permits the recording of isotonic forces of contraction. When using the locked brace mode, measurements of isometric muscle are also possible. The brace is a suitable and low price research tool. Its construction could be easily adapted to the experiments on animal legs of different sizes and force of contraction. Acknowledgement This work was financed by Research Grant Nos. J2-7042-1326 and J3-2389-0381 -00 from the Ministry of Science and Technology, Ljubljana, Republic of Slovenia. References /1/ Bunc, M., Suput, D., Rozman, J., 1999, Force transducer for measurements of Isolated muscle contractions. J Med Eng Technol, 23, 222-225. /2/ McNeal, DR., Bowman, BR., 1985, Selective activation of muscles using peripheral nerve electrodes. Medical & Biological Engineering & Computing, 23, 249-253. /3/ Sweeney, JD., Ksienski, DA., Mortimer, JT., 1990, A nerve cuff technique for selective excitation of peripheral nerve trunk regions. IEEE Transactions on Biomedical Engineering, 37, 706-715. /4/ Lefurge, T., Goodall, E., Horch, K., 1991 Chronically implanted in-trafascicular recording electrodes. Annals of Biomedical Engineering, 19, 197-207. /5/ Rozman, J., Sovinec, B., Trlep, M., Zorko, B., 1993, Multielectrode spiral cuff for ordered and reversed activation of nerve fibres. Journal of Biomedical Engineering, 15, 113-120. /6/ Rozman, J., Zorko, B., Seliskar, A., Bunc, M., 2000, Selective recording of ENG from peripheral nerve. Pflüg Arch-Eur J Ph (sup-pi), 440, 157-159. /7/ Rozman, J., Zorko, B., Bunc, M., 2000, Selective recording the sciatic nerve of a dog with multi-electrode spiral cuffs. Jpn J Physiol., 50, 509-514. Matjaž Bunc School of Medicine Institute of Pathophysiology Zaloška 4, 1000 Ljubljana, Slovenia e-mail: Bunc@ibmi.mf. uni-lj. si fax: 386 61 443 898. Janez Rozman ITIS d. o. o. Ljubljana Centre for Implantable Technology and Sensors Lepi pot 11, 1001 Ljubljana, Slovenia Tel.: 17 01 913, Fax.: 17 01 939 Prispelo (Arrived): 28.03.01 Sprejeto (Accepted): 01.06.01 109 Informacije MIDEM 31 (2001 )2, Ljubljana UDK621,3:(53+54+621 +66), ISSN0352-9045 APLIKACIJSKI ČLANKI APPLICATION ARTICLES TANTALUM CAPACITOR REPLACEMENT WITH CERAMIC CAPACITOR Iztok Sorli, MIKROIKS, Ljubljana High Capacitance MLCC For several years we have been facing periodic variations of availability and price of Tantalum capacitors. In the past this behaviour was due to political and economical strategies. Today it is the poor supply of Tantalum raw material that drives the Tantalum capacitor crisis. At present we see a price growth of 50% (from 0.2 USD to 1.0 USD) for normal Tantalum capacitors; the forecast is for a further hike in the next year. Murata can help to solve this problem by offering many ceramic capacitors that directly replace electrolytic and Tantalum types. Before we discuss about electrical characteristics, part numbers etc., let us briefly summarize some basic concepts of high capacitance usage. Figure 1 shows principal circuits that need high capacitance values. Smoothing The function of C1 and C2 is to smooth ripple and voltage fluctuations at the input and output of the LDO (Low Drop Out Regulator). C2's ESR and ESL are most important because they are responsible for the purity of the output voltage. In the past high value Ta capacitors were used; now it is possible to use ceramic capacitors at 1 /2 to 1 /10 of the Ta values used. not polarized in order to avoid signal distortion. What better solution than a ceramic capacitor? Smoothing LDO CI C2 Bypass Coupling R2 Q2 C4 Figure 1: R3 Examples of principal circuits where capacitors with high capacitance values are mostly used Bypassing C3 creates a "virtual" ground for the transistor which "believes" it is working at ideal conditions. The static and dynamic parameters are satisfied and the active device is properly used. Also in this case the ESL of the capacitor is of the most importance since a low value avoids self - oscillation problems. Coupling In order to link two stages (for example pre amp to power amp) C4 is basic. This capacitor transfers only the signal and does not modify the DC parameters. For the example mentioned, it is the most important that the capacitor is Technical Aspects of Multi Layer Ceramic Capacitors Despite the simple construction, monolithic ceramic capacitor provides both high-speed response and an excellent high-frequency characteristics; the capacitance range has generally reached just approximately 1 jj,F until now. However, with recent advancements in the thin-layer/multilayer forming technology for dielectrics, as well as the technology for using base metal for internal electrodes, the capacitance range now exceeds 1 |iF. Moreover, capacitors with capacitance of up to 100jiF have been developed and are now being used. 110 I.Sorli: Tantalum Capacitor Replacement by Ceramic Capacitor Informacije MIDEM 31(2001)2, str. 110-114 Multilayer Ceramic Capacitors (MLCC) are built as a kind of "sandwich", composed of conductive layers separated by a dielectric (ceramic). Two conductive terminations are added to provide solderability, figure 2. The mathematical formula that relates all the mechanical and electrical parameters to the capacitance values is as follows: C = - 8 X80xSxn d where * £o: dielectric constant of vacuum * e: dielectric constant of ceramics * S: active area per layer n: number of ceramic layers * d: thickness of a layer With this equation in mind, the means of obtaining high value multilayer ceramic chip capacitors are: * thinner dielectric layers * Increased number of dielectric layers * increased active area * increased dielectric constant The most important parameter that can enable an increase in the capacitance of monolithic ceramic capacitors is the thickness of the dielectric element. Year by year, the dielectric element thickness becomes ever smaller. Currently, products with a dielectric element of 2 ~ 3 ¡im thick are on the market, and recent products with dielectric elements only 2|im thick or less have been developed. The core technologies for supporting thin-layer products include technologies for ultra-fine graining and low-temperature firing of ceramics, non-reduction material technology, and technologies for graining and dispersing the electrode material, as well as using base metal for the electrode material. These technologies are much advanced compared to more conventional ones. Consequently, the delicacy of a MLCC design is clear. A good capacitor is the result of a good balance between materials, thickness and dimensions. This demonstrates the difficulties to be overcome in order to obtain small, high value capacitors with good temperature performance and high working voltages. Reliability Superiority of Ceramics over Tantalum TERMINATION CERAMIC UNIT INNER ELECTRODE A - A'CROSS SECTION B Breakdown voltage In figure 3 there are two important points that must be observed: * considerably higher actual breakdown voltage of ceramic capacitors compared to tantalums * enormous safety factor between stated working voltage and actual breakdown voltage of ceramic capacitors This only means that the ceramic capacitor is more reliable and that can safely operate at the stated working voltage; It would also seldom fail due to overvoltage spikes which would kill tantalum capacitor. Fugure 2: Structure of a ceramic capacitor A) device cross section B) physical cross section as seen on electron microscope; the graph is showing how higher capacitances ofX7R and Y5Vceramic capacitors can be obtained by thinning dielectric layers and by increasing their number 111 Informacije MIDEM 31(2001)2, str. 110-114 I.Šorli: Tantalum Capacitor Replacement by Ceramic Capacitor Sample (1) MLC X7R 1 ¡X F 10V (GRM40X7R105K10) (2) MLC Y5V 4.7/; F 16V (GRM42-6Y5V475Z16) (3) MLC Y5V 4.7^ F 16V (GRM230Y5V475Z16) (4) MLC Y5V 10 n F 16V (GRM235Y5V106Z16) (5) TA 1 ¡x F 16V (A case) (6) TA 4.7 ¡jl F 16V (B case) (7) TA 10 fi F 16V (C case) 500 400 300 B MLC X7R I ^ F 10V MLC Y5V 4.7 /i F 16V MLC Y5V 4.7 /i F 16V MIC Y5V 10ÍÍF 16V 1 ¡i F 16V S 4.7/iF 10V S 10/J F 16V S (1) (2) (3) (4) (5) (6) (7) Figure 3: Comparison among measured breakdown voltages of ceramic and tantalum capacitors ESL & ESR vs Frequency Unique features of ceramic capacitors are their low Equivalent Series Resistance (ESR) and Equivalent Series Inductance (ESL) especially at high frequencies. This is clearly demonstrated in figure 4 where differences among two types of ceramic (X5R and Y5V) capacitors and tantalum capacitors are shown. The superior performance of the ceramic is extremely clear, allowing optimization of final circuit. Because of this effect, in most cases it is even possible to reduce the capacitance values of ceramic capacitor compared to tantalum, while filtering very effectively. 100 100m - - - Est MLCC 1206 XSR I0hF6.3V - - - ESEMLCC 1206 Y5V 10)/6.3V - - - ESLIA iOjjF 16V -ESE MLCC 1206 X5R lOpE 63V -ESR MICC 1206 ÏSV 1 OpF 6.3V _ ESE 1A lOjjf 16V MICC^T ! IM IM frequency (Hz) Figure 4: ESL and ESR of ceramic versus tantalum capacitors The low ESR (at medium/high frequencies) also causes low self-heating when ceramic capacitor is under stress at high frequencies and under high voltage. Figure 5: Attention Temperature rise of different capacitors working at 100 kHz When designing circuitry with ceramic capacitors two important things must be taken into consideration: capacitance versus temperature behaviour of different ceramics, as well as capacitance versus bias voltage dependence, as summarized in figures 6 and 7. In these two specific cases only the performance of X7R ceramics is comparable to tantalum, while Y5V is inferior. Specification TÇ Temo, ranne Can. chance from 25'C X7R -55 - +125*C + 15% Y5V -30 - +85'C +22/-82% - MLC X7R 1 ¡j. F - MLC Y5V 4.7//F 16V " ' TA 1 ^ F 4.7 y. F Figure 6: 0 25 50 75 TEMPERATURE ("C) Capacitance versus temperature behaviour of different capacitors Allowable Power The low ESR is the feature of MLCC that allows high peak current. This guarantees very fast response to high speed current transients. 112 I.Sorli: Tantalum Capacitor Replacement by Ceramic Capacitor Informacije MIDEM 31(2001)2, str. 110-114 -»-MLC 0805 X7R 1 /¿F 10V/GRM40X7R105K10 ^MLC 1206 X7R 1 16V/GRM42-6X7R105K16 —-MLC 1206 4.7 ¿Í F 16V/GRM230Y5V475Z16 ■»■ TA A case 1 //F 16V Figure 7: 10 12 DC VOLTAGE (VDC) Capacitance versus DC voltage behaviour of different capacitors Measurement results Figures 8, 9 and 10 present some measurement results from which we can compare performance of ceramic to Ta/AI capacitors in pulse response, noise absorption and smoothing applications. This data shows clearly that in noise bypass applications the value of MLCC capacitance can be 1 /2 to 1 /10 of the tantalum for the same bypass effect. This is due to lower ESR and ESL of MLCC compared to tantalum capacitor. INPUT PULSE (500kHz) OUTPUT WAVEFORM SM- 5 [V] AV=3[V] DUTY=50[%] — 2 [i; secj ■ i / AV=64 [mV] MLC 1pF (GRM42-6 X7R 105K 16) MEASURING CIRCUIT O-Wr- 50 ohm c TA 10uF AV=69 [mV] PULSE GENERATOR: HP 8112A DIGITIZING OSILLOSCOPE: HP 54111D AV=233 [mV] AL10uF u Input Pulse Freq Input Pulse Voltage Output ripple voltage (mV) AL TA MLCC 10kHz 534 204 196 100kHz 2V 336 64 16 500kHz 346 38 12 1MHz 332 30 3 FFT Analysis result shows MLCC's superiority in terms of noise absorption in High Frequency range. AL 10nF iHMni.v- HállWfiil ■--j-'1-fl-juffi ... «.... TA 10nF MLCC 10pF Figure 9: General noise absorption comparison data Nod resonance type forward method DC - DC converter. WW ~ ' fi't*?" " '4ÉM Olilpat : 5\ / 2 A Í IfïW ) cCircuit Diagram>