The Design Of Digital Down-Converter Based On FPGA

The DDC (Digital Down-Converter) in Software Radio system can reduce the rate of data flow, and send this low-speed data to the DSP devices which can process this data fluently. DDC as a bridge between the ADC and the DSP devices, its performance will have a direct impact on the stability of Software Radio system. The dedicated DDC chips have many advantages, such as the stable performance and the higher proportion of extraction, but the high price and the weak flexibility can't fully reflect the features of the Software Radio.Due to the rapid development of FPGA, the performance of FPGA has been greatly enhanced. Relative to the ASIC and DSP, FPGA's high-throughput, short development cycle and online remodeling making it plays an important role in Software Radio's researchment and development.The design aim is to realize a single channel DDC chip with FPGA. The implementation of the DDC in Software Radio system base on FPGA has been analyzed. The main modules' design and simulation have been completed. The preliminary system-level verification also completed.In this thesis, the DDC's current technology at home and abroad was analyzed, and then the advantages of using FPGA to complete the design of DDC were described. This paper focuses on the principle and the architecture of the DDC based on the research of the theory of the Software Radio and the Digital signal Processing. The implementation of the modules of NCO, Mixer, CIC, HB, FIR filter was analyzed. The whole system's structural and the modules' division, interface definition, mathematical simulation, optimization was completed in MATLAB. Through the simulation, the system architecture was optimized in order to get the performance balance between each module and the whole system. Finally, the simulation and debugging of each module was completed by using the Verilog programming and part of IP core. The results showed that the design and structure is correct, the next step will be the debug on the DDC board.