Design And Implementation Of Vector Signal Generator Based On FPGA

Vector signal generators are widely used in the testing of radar,mobile communication,electronic circuits and other systems due to their rich signal types and flexible and controllable carrier frequency.Therefore,the design of vector signal generator based on FPGA platform and its performance optimization have gradually become a research hotspot in related fields.A vector signal generator is designed based on the zero-IF structure.FPGA is used as the real-time generation platform of the baseband signal generator.The digital baseband signal generated by FPGA is converted into analog signal through DAC,then the low frequency baseband signal is mixed by the quadrature modulator to the radio frequency.Based on the quadrature modulation method,the realization principle of a variety of general modulation signals and the digital standard FDD-LTE signal of the 4G communication system specification is analyzed in detail,and an implementation framework that is easy to be processed by FPGA is designed.After testing and verification,the output waveform of the designed vector signal generator covers a variety of modulation signals such as AM,PM,FM,multi-tone,QAM and FDD-LTE.The carrier frequency is adjustable from 500 MHz to 6GHz.The non-ideal characteristics of the quadrature modulator are analyzed,the linear distortion and nonlinear distortion models of the quadrature modulator are established,and the linear distortion correction is completed in the DAC device.After linear distortion correction,the maximum EVM of the digital baseband modulation signal is reduced from about 2% to about 0.4% in the frequency band from 500 MHz to 3.5GHz,and the maximum EVM of the FDD-LTE signal is reduced from about 1.6% to about 0.4% in the frequency band from500 MHz to 6GHz.The fluctuation of EVM is small in the whole frequency band,the performance of the modulated signal is excellent.For the situation that nonlinear distortion has a greater impact on the system in the high frequency,based on the recursive least squares(RLS)algorithm,the fitting of the quadrature modulator complex coefficient polynomial model is completed,and the nonlinear distortion model of the quadrature modulator is established.