The Design Of A Local Oscillator For Digital Television Transmitter

The construction of DTTB(Digital TV Terrestrial Broadcast) network is being carried through in China these years. The market of the key part—transmitter is controlled by foreign companies. Many domestic companies began to develope DTV(digital TV) transmitter in order to put down the cost and own the core techniques. The author's main work is the development of the LO(local oscillator) in DTV transmitter, it is one of the important research projects planned by Shanghai Mingzhu Company. The author presented a new scheme that combined the techniques of multi-loop PLL(phase-locked loop), assistant frequency discriminate, DDS, analog PLL. That scheme helped us to realize a wide band frequency synthesizer with very small steps. We use the ADS software to help the designing of a 470-860MHz frequency synthesizer prototype. The test result showed that the main specifications reached or closed to the foreign products. According to the order of Shanghai Mingzhu Company, I also designed a narrow band frequency synthesizer with a 200KHz step. The core is ADI's PLL IC ADF4360-7. The test result showed that this synthesizer could achieve at least 10% bandwidth and throuth changing external inductor could cover 175-1800MHz. Its phase noise, stability and bandwidth etc. all reach the requirements. The advantages of this scheme are low cost, short design period, flexibility and could turn to products quickly.