Design And Implement Of The Digital Unit Of Spectrum Analyzer Based On FPGA

Terahertz spectrum analyzer plays an important role in atmospheric trace gas observations, life sciences, safety testing and other aspects of applications. The development of terahertz technology put forward higher requirements for Terahertz spectrum analyzer in bandwidth, spectral resolution and stability. This theis is intended to design a spectrum analyzer digital unit based on FPGA in this background, hoping to be applied in areas such as limb sounding, and provide a technical basis for the research.Terahertz spectrum analyzer in the development process is mainly produced four kinds of spectrum analyzers. Early multi-channel spectrum analyzers are filter banks. A power divider splits the input signal into several or many input channels, each channel has a separate bandpass filter and power detector. This kind of spectrum analyzer is expensive, requiring strict control of mechanical tolerances, easily leading to channel crosstalk, so it has been replaced by other technologies. Then came the acousto-optical spectrum analyzer with small size, low power consumption characteristics, its maximum bandwidth is in the range of 1 to 2 GHz, with the spectrum channels of thousands of Bragg cell material. The drawback is the structure is complex, demanding strict work environment, thus limiting their use in high-precision measurements in space. With the development of broadband multi-bit high-speed ADC, ADC sampling rate can reach 2.5GHz to 10 GHz. Recent years Xilinx FPGA high-speed storage and real-time digital signal processing capability has greatly increased, the FFT IP core’s function has gradually improved, and its performance has substantially increased, which make the design of ultra-wideband, high resolution FFT spectrum analyzer possible.In this thesis, after the research about the spectrum analyzer and FFT principle, the author proposed a design scheme of terahertz spectrum analyzer digital unit based on FPGA. Firstly this thesis introduced THz spectrum analyzer development, and summarized the realization principle of the analyzer. Then it gave a detailed descriptions of the hardware and software design of the spectrum analyzer digital unit. The hardware part of the digital unit complete 2.4 GHz signal sampling with four ADCs, complete the multiplexing and FFT spectrum operation with a FPGA chip, in which ADC selecting ADC083000, FPGA chip selecting Xilinx Virtex-5 series. The software part gave a detail introduction of the software system architecture, data flow and some experimental results. The function of each part of the system is controlled by VHDL programming. The main function modules include clock module PLL three-line programming module, multiplexing module, FFT module, FIFO and serial transmission module. Functional verification through ChipScope tool, the digital unit is stable and reliable, it can be applied to the limb sounder.