Broadband Variable-rate Digital Inverter Technology

With the development of satellite communications, it is more and more important for the equipments to be flexible and opening. It has become the best choice and certain direction to keep up with the development of the technology and requirement that using Software Ratio(SR) technic design modulator and demodulator in satellite communication system. Now demodulator is facing the change which enable analog-to-digital converter activating from in baseband to in intermediate frequency(IF). This article mainly focused on designing digital down-converter(DDC) in satellite communication receiver which received broadband and rate changeable signal. In addition, the article simulated and analyzed the receiver's performance. The main content of this article includes:Firstly, author founded the model of digital demodulator with the software radio architecture to receive satellite communication signal and designed the hardware;Secondly, author mainly investigated the decimation filter and digital sampling rate conversion(SRC) in DDC. Author present a conception for multi-stage decimation implement and a method to realize SRC with polyphase filter for higher demodulating performance;thirdly, author realized a digital demodulator by software include floating-point and fixed-point, and tested the performance by demodulated the real signal;Finally, author put the fixed-point software into FPGA, and debugged the importantmodules.