Research Of Multi Channel Digital Down Conversion Based On FPGA

This paper improves a digital frequency conversion system,in the light of noise and aliasing shortcomes through the signal extraction process at the field of electronic technology and communication technology at present.This system enhances the anti-aliasing by increasing the series on the FPGA chip and reduce the orders,it not only reduces the complexity of the design,saves the cost and energy consumption,but also the FPGA chip's reconfigurability brings to the DDC system a flexible real-time update.Based on the signal's basic sampling theory,this paper researches scheme of multi-channel digital down conversion based on FPGA.Analyze the basic algorithms of signal process and the realization methods of each part.Adopted top-down module analysis method,this paper investigates the important components of the DDC system detailedly,such as numerical control oscillator module,mixer module,filter module,half band filter and finite impulse response filter module.This system designs and simulates each subsystem based on the FPGA platform,designs the NCO module and mixer module with the VHDL language program and IPcore macro module on the Quartus?software,designs the filter module with the Matlab FDAtool and IPcore macro module,transfers every module to the Matlab software simulation test in order to validate the purposes of the design at last.Each module will be analyzed as follows,the numerical control oscillator is achieved with CORDIC algorithm and it generates signals faster and less resource;the mixer module is used the multiplication principle and it reduced utilization of the chip pin;the comb filter group makes up of the original comb filter(CIC)supplement,using delay and shift statement to reduce the demand of logic-gates;finite impulse response filter module shapes the signal in the channel,by compared the two kinds of filters of linear and window function to select the optimal treatment method.Test of this system shows that the program can achieve a complete digital down conversion function,and it can undistort restore the input signal.The numerically controlled oscillator reduces the pin utilization by using the iterative pipeline scheme;CIC combination filter controls the passband attenuation and makes the band contentdifference reduced to less than 0.5dB at the same time;tested by matlab software,the FIR filter based on window functions can remove the aliasing noise and reduction the effective signals at the same time.The whole test results meet the requirements of the design and can achieve the goals.