Design And Implementation Of FPGA Digital IF Card

Software radio is a hot research topic in the field of modern communication, anddigital IF is one of the key technologies for the software radio. Because the deviceperformance is not good enough, convert radio frequency to intermediate frequency,sample and process IF signal. FPGA has high performence of the special integratedcircuit and flexibility of DSP. So FPGA plays an increasingly important role in thefield of digital signal processing. FPGA has been widely used in wirelesscommunication system. Using FPGA to realize the digital intermediate frequency, cancoordinate the contradiction between processing capability and flexibility. This paperresearches the method of realizing digital IF by FPGA, and analyzes the hardwaredesign and software design of the system in detail.Firstly, this paper introduces the research background of digital IF, describes thebackground of the software radio and application of FPGA in digital IF domain, andanalyses relevant principles of digital IF including DUC, DDC, CIC decimation filter,CIC interpolation filter, compensation of CIC filter and digital control oscillator andso on. Secondly, this paper accomplishes the design of the schematic diagram andPCB, and analyzes the design of ADC module, DAC module, FPGA, MCU, clockmodule and power module in detail. We debug and test the hardware module to ensurethat the bandwidth, slew rate, amplitude and impedance of ADC/DAC module meetthe system requirements, power module provides high quality power, and the outputof clock module meets the system requirements. Then, this paper accomplishes theFPGA software design of the digital IF, and analyzes the design of DUC, DDC, CICdecimation/interpolation filter, FIR compensation filter and NCO in detail. Weexecute functional simulation of each module from bottom to top. Simulation resultsagree with the theoretical results. The result of FFT analysis shows that the waycascading CIC filter and FIR filter has a good effect. The combination has a simplestructure, and can be implemented by FPGA easily. Finally, we verify the digital IFsoftware through the FPGA device. The result of spectrum analysis closes to thetheoretical value, as well as the amplitude and circle of waveform. This verifies thecorrectness of the DUC. Connecting the output to the input, the output of DDC issimilar to the input of DUC. This verifies the correctness of the DDC.