379 KB18 KB198520252007Kosi, AndrejSolar, Mitjaštevilka:1letnik:37str. 38-41ISSN:0352-9045COBISSID:11553046URN:URN:NBN:SI:doc-ZKP6U8WJslStrokovno društvo za mikroelektroniko, elektronske sestavne dele in materialeInformacije MIDEManalogni signalidigitalni signalitelevizijska tehnikaHibridni oscilator za analogne in digitalne prizemeljske televizijske oddajnike|Currently, the transitien or preparation for the changeover from analog television to digital television is in progress. Consequences of this transitien are modifications that will have to occur in the distribution, transmission and recepti on of television signals. This article will mainly focus on television transmitters, or more precisely to their oscillator. The demands for oscillators used in digital television are different from those used in analog television and for this reason, simple modification of the latter is not possible. The major differences are in the small est frequency step and phase noise demand. The smallest frequency step for digital television is 1 Hz, which is far less than the few kHz step required for analog television. The phase noise requirement is specified in the standard for DVB-T (Digital Video Broadcasting - Terrestrial) and is al so higher than that for analog television. This article will present the hybrid oscillator, which is suitable for use in both analog and digital transmitters. The term hybrid oscillator refers to an oscillator that combines two or more different technologies together. In this case, the hybrid oscillator combines direct digital synthesizer (DDS) and phase locked loop (PLL). The advantages and disadvantages of DDS and PLL are shortly presented. DDS output is limited with frequency range, frequency spurs and harmonics. On the other hand, DDS has a fast settling time and a very fine frequency step ( Hz). PLL can be used for higher frequencies with a wider frequency range, however it is hard to achieve a small frequency step, low phase noise and fast settling time at the same time. This is because the improvement ofone parameter degrades the others. For our hybrid oscillator, DDS is used as a source for the reference frequency of the PLL. In so doing, fine frequency step is achieved and the wanted phase noise is preserved. For best results it is very important to use high quality electronic paris that contribute little to phase noise degradation. On the basis of conclusions, we have made a prototype of this hybrid oscillator for UHF (Ultra High Frequency) frequency band. In addition, a number of different measurements of the hybrid oscillator were taken to confirm theoretical calculations and expectations. The final measurement results have shown that the hybrid oscillator is suitable for use in both analog and digital television transmitterTrenutno poteka ali se pripravlja prehod oddajanja analognega televizijskega signala v oddajanje digitalnega televizijskega signala. Časovno je ta prehod v evropski uniji okvirno določen, od posameznih držav članic pa je odvisno, kdaj ga bodo izvedle. Prehod je povezan z velikimi finančnimi investicijami, zato so zanimivi oddajniki ali sklopi oddajnika, ki jih lahko uporabimo tako v analognem kot digitalnem načinu oddajanja. Eden od sklopov oddajnika, ki ga je treba v tem primeru prilagoditi ostrejšim zahtevam, je oscilator. V prispevku je predstavljen hibridni oscilator, primeren za analogne in digitalne prizemeljske televizijske oddajnike in kanaine pretvornike. Analogna omrežja so v osnovi večfrekvenčna, kar pomeni, da so sosednje oddajne celice na različnih frekvenčnih kanalih. Digitalna omrežja pa so lahko večfrekvenčna, enofrekvenčna ali kombinacija obeh. To ima za posledico, da so zahteve za oscilator v digitalnem oddajanju zahtevnejše. Zadani cilj je bil razviti oscilator, ki bo izpolnjeval zahteve na tržišču glede lastnosti takšnega oscilatorja. Predlagano rešitev smo poimenovali hibridni oscilator. Hibridni oscilator združuje dva koncepta, ki se uporabljata za generiranje frekvence. En koncept je fazno sklenjena zanka, drugi pa sintezator z neposredno sintezo signala (v nadaljevanju DDS-oscilator). Z nobeno od obeh metod ni možno enostavno izpolniti vseh zahtev za oscilator. Bistveni zahtevi sta predvsem korak nastavljanja izhodne frekvence in fazni šum oscilatorja. Z združitvijo dobrih lastnosti obeh metod je mogoče narediti, oscilator z želenimi lastnostmi. DDS-oscilator je uporabljen kot vir signala z referenčno frekvenco za fazno sklenjeno zanko. Z majhnim spreminjanjem frekvence DDS-oscilatorja dosežemo večjo frekvenčno ločljivost fazno sklenjene zanke, s katero pa lahko pokrijemo frekvenčna področja, ki jih ni mogoče neposredno pokriti z DDS-oscilatorjemTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaStrokovno društvo za mikroelektroniko, elektronske sestavne dele in materiale