The Technology Of Digital Down Converter Base On FPGA

Most of commercial radio equipment is made of ASIC,which can run in high speed,but ASIC has a long development cycle and an inconvenient modification of function.The emergence of Software Defined Radio(SDR)make things easier,in addition to modules that must use hardware to achieve such as antennas,amplifiers,mixers and AD/DA,others can be implemented in software.So that developers can program to achieve or change the function of radio,without having to modify the circuit,so will greatly improve the design efficiency.Digital Down Converter(DDC)is a very important part of SDR,it converting frequency and connecting the RF and DSP side,also is the key to build SDR system.This thesis is about DDC of SDR.DDC system mainly includes down-conversion module,sample rate conversion module and low-pass filter module.In the study of the DDC,it is found that for the input signal in a certain frequency range,the design of the sampling rate conversion module is different,but the design of rest basically the same.In other words,for different input signal,DDC only need to design a different sampling rate conversion module,and other modules can be multiplexed.Based on this,this thesis designs a five-channel DDC system,which can handle five different frequency input signals.This multi-channel is the innovation of the design.First,the basic theory of DDC technology and some key technologies are introduced in the thesis.Then introduced the realization of each module in DDC,including mixing module,sampling rate conversion module,LPF module and so on.After that Modelsim software was being used to simulation verification,ensure correct design by analyze the time domain waveform,and MATLAB was used to analyze the data,the frequency domain waveform,to ensure that the performance of module.Finally,FPGA was used to simulate and verify the system designed to ensure the rationality of the design.