Research And Implementation Of Wideband Digital Intermediate Frequency Technology In Real-Time Spectrum Analyzer

With the rapid development of wireless communication technology, the detection and management of the electromagnetic spectrum become more and more important. The real-time spectrum analyzer provides a strong guarantee for spectrum monitoring work. The establishment of wideband digital intermediate frequency system in real-time spectrum analyzer accelerates the research of broadband signal spectrum analyzer in our country. The specific contents are as follows.Firstly, the paper expatiates on the basic theory of digital IF processing technology, followed with discussions on the theory of signal sampling, digital down converter, sampling rate transform and FFT. Then we put forward a scheme suitable for wideband digital intermediate frequency processing system implemented in FPGA. The processing module firstly uses the bandpass sampling theorem to sample analog IF signal, and makes the IF signal transform to baseband signal, then uses decimation filters to decrease the data rate and ensure the analyzed signal without distortion, finally the FFT realizes the spectrum measuring function.Secondly, the paper discusses the design and realization of each module in FPGA. In digital down conversion module, it proposes a new kind of digital mixing algorithm. Using the new algorithm we can design a digital mixer without any hardware multiplier. Then it designs a new lowpass decimator filter with only a handful of multiplier and realizes the digital mixer and filter in FPGA. In sampling rate conversion module, it puts forward a structure of 1-2 times decimation filter based on the Sine interpolation algorithm theory. Then we use 1-2 times decimation filter and half band filter to convert sampling rate at arbitrary times in FPGA. In FFT module, it discusses the frame and window in FFT and has a detailed analysis of FFT IP core.Thirdly, the paper discusses the hardware structure of the broadband digital IF system. The IF system has four modules:digital IF signal processing module, large capacity data storage module, PCIe module, and DSP module. It presents schematic diagrams of each module and PCB digrams of the broadband digital IF system. Then It mainly introduces the digital IF signal processing module including the process of sampling and data transmission between ADS5474 and FPGA.Finally, we have a software simulation and hardware functional verification for the wideband digital IF system. We use ModelSim simulation software to simulate each module in FPGA, and set up a real test platform for the test. Then we use Matlab for data analysis.