Design Of Channel Correction Module For Baseband Signal Generator

I/Q baseband signal generator plays an important role in modern communication system.Independent baseband sources must meet a wide range of test requirements,and good channel characteristic are one of the main links to ensure good signal quality.The 80 MHz I/Q baseband signal generator channels in this paper mainly consist of two parts,DAC(Digital to Analog Converter)and Analog channel.The digital baseband signal is output from the FPGA(Field Program Gate Array)and sent to the DAC to be converted to an analog baseband signal,and then reconstructed and filtered through the analog channel.Due to the frequency response of the channel,the output signal is distorted,resulting in the deterioration of indicators such as EVM(Error Vector Magnitude)when evaluating the baseband signal.In order to reduce EVM value and bit error rate,the amplitude frequency characteristic and phase frequency characteristic of the I/Q channels are studied,and the corresponding amplitude frequency compensation filter and phase frequency compensation filter are designed.The FIR(Finite Impulse Response)filter is implemented in the FPGA.The waveform data is preprocessed to reduce distortion after the waveform passes through the channel.The main research content and work of this paper are divided into the following parts:1.According to the characteristic of baseband signal generator board,the corresponding measurement scheme of amplitude frequency response and phase frequency response is developed,and the frequency response of baseband signal generator I/Q channel is analyzed in detail,and the overall correction scheme is given.2.The amplitude-frequency compensation filter and the phase-frequency compensation filter are studied.The amplitude compensation function and phase compensation function of the required design are obtained by derivation analysis.When designing the amplitude-frequency compensation filter,the window function design method and the frequency sampling design method are studied.When designing the phase compensation filter,the Maximally Flat FIR FD Filter and the fractional delay all-pass filter are studied.3.The multiply-accumulated structure and the distributed structure digital filter are briefly analyzed,and a detailed FPGA implementation scheme is developed.The amplitude compensation filter module and the fractional delay variable Farrow filter module are completed in the FPGA.4.In Matlab,QAM,FSK,PSK and other digital modulation baseband signals are generated.The signal is sent to the input end of the channel through the control of the host computer,and the EVM and other indicators of the baseband signal are measured at the output end.The EVM values before and after correction are compared.Make sure the corrected EVM is within 1 %.