Design And Implementation Of IF Processing Of Real-Time Spectrum Analyzer

With the rapid development of broadband wireless communication technology,the frequency range of various electronic signals is getting higher and higher,frequency of carrier transmission is higher, burstiness and complexity are also increasing. Test equipment with traditional spectrum analysis technique has been difficult to deal with detection challenges with high bandwidth, high precision,real-time or multi-burst. This thesis designs and implements the digital IF processing module with high bandwidth signal sampling, real-time data processing which based on the digital intermediate frequency processing technique.This thesis firstly discusses the all-digital IF processing technology, analyzing the broadband signal sampling theorem, digital down-converter, technology of overlapping frame and Fast Fourier Transformation. On this basis, combined with the test requirements, the IF processing module is designed for spectrum analysis and modulation domain processing.1. The analog signal high-speed sampling module includes the logic design of sampling clock, anti-aliasing filter design and receiving logic design of ADC sampling data. Firstly, a band-pass filter is designed which based on the bandpass sampling theorem. And the ADC sampling clock is configured with FPGA, and digital IF signal is received, processed and transmitted.2. According to the requirements of different signal test, the signal is moved to zero frequency from the intermediate frequency which based on the serial down-conversion technology. Based on the filter down sampling technology, a decimation filter structure with variable extration rate is designed to get low-rate baseband signal under the premise of ensuring that the data is not distorted for obtaining multi-rate signals that meets different analysis bandwidths.3. Frame overlap mathod of dual FIFO. Overlap frames technology is one of the key technologies in real-time spectrum analysis. This thesis has designed the overlapping algorithm which is based on dual FIFO. Baseband signal is windowed,which means being multiplied with the time domain window function coefficients, in the format of data frame to the real-time FFT for spectrum analysis and processing.4. Logic design of Amplitude and phase computation. Real-time FFT processing technology is the core technology of real-time spectrum analysis. This thesis firstly introduces the Fast Fourier Transform theory, designing and adopting the pipeline structure to realize the real-time processing of the data. And then amplitude and phase informations of the signal are obtained by CORDIC algorithm.5. According to the design requirements of the project, the matched filter with re-load factor is designed, and the modulation signal is extracted and matched, and the channel SNR is maximized to realize the modulation domain processing of the signal.Based on the simulation of logic function of Modelsim, this thesis analyzes each part of the above design by the hardware platform, comparing the theoretical and actual values to verify that the functions of the IF spectrum processing module and Matched filter module have basically met the requirements.