Design Of A Digital Down Conversion Based On FPGA

With the progress of science,the development of society,software radio came into being.In software radio,the traditional hardware radio communication equipment is only used as a basic platform for wireless communications,and many of the communication function are implemented by software,it breaks the pattern that the realization of communication history of the equipment is only depends on the hardware development.Due to the limitation of the current hardware level,the DSP processor can not directly deal with the data from the A/D sampling,so digital down conversion is an indispensable part of the software radio.In 21 Century,programmable logic devices have been developed to a very mature stage,and the FPGA(field programmable gate array)is the most perfect development one.Now the design of electronic circuits is basically based on the FPGA.Using FPGA design digital down conversion is also very convenient.Firstly,this article introduces and studies the basic theory of digital down conversion: Sampling theory and multi rate digital signal processing theory.Compared with the NCO generation algorithm and its performance,this article focuses on the characteristics of CORDIC algorithm and its advantages.Then this article studies the theory,structure and implementation method of NCO(digital control oscillator),CIC(integral comb filter),HBF(half band filter),FIR low pass filter based on FPGA.In the design process,In this paper,this article uses Modelsim to simulate and debug each module,and use Matlab to do spectrum analysis.Finally,the AD company's AD9280 chip and the Altera chip EP4CE15F17C8 are used together with Matlab's FDAtools to design a 0.1-0.4MHz input signal and the sampling frequency of 32 MHz digital down converter,in this article,Spectrum Analyzer and Signal Generator are used to do the board level test.