傅里叶变换光谱相位校正的FPGA实现方法

傅里叶变换光谱仪因具有分辨率高等优点已被用于新一代大气垂直探测仪。这种光谱仪获取的数据量很大,只有进行星上数据处理才能降低数据发送量。方法之一是在轨光谱复原。由于非零光程差采样等原因使采样干涉图存在相位差,经傅里叶变换得到的复数光谱需进行相位校正以获得实数谱。FPGA(Field-Programmable Gate Array)是一种很有应用前景的星上数据处理硬件平台。阐述了相位误差的来源及几种相位校正方法。平方根法适于FPGA硬件实现。针对采用传统方法计算平方根时需要很多硬件资源及精度较差的问题,提出采用CORDIC(Coordinate Rotation Digital Computer)算法完成复数光谱模值和相位角的计算。重点论述了CORDIC算法的FPGA实现结构,分析了其实现的精度、速度和所需的硬件资源。结果表明,采用CORDIC算法计算,复数光谱的相位和模值具有很好的精度和速度,所需的硬件资源较少。

Implementation of Phase Correction for Fourier Transform Spectrum Using FPGA

Because of the advantages of high resolution etc, Fourier transform spectrometers have been used as a new generation of atmospheric sounders. Such a spectrometer will acquire a very large quantity of data. To reduce the amount of the data to be transmitted, the data should be processed on board. One of the methods is use of in-orbit spectral recovery. Since there exists phase difference in the interferograms sampled by non zero optical path difference sampling, the complex spectra obtained by using Fourier transformation should be corrected in phase so as to generate the real spectra.The Field-Programmable Gate Array (FPGA) is a promising on-board data processing hardware platform. Phase error sources and phase correction methods are presented. The square root method is suitable for a FPGA to implement. In view of the problem that a lot of hardware resources are needed and poor precision is obtained when the square root is calculated by using the traditional method, a Coordinate Rotation Digital Computer (CORDIC) algorithm is proposed for the calculation of complex modulus spectrum and phase angle. The FPGA implementation structure of the CORDIC algorithm is mainly discussed, and the required precision, speed and hardware resources are analyzed. The results show that the phase and modulus of complex spectra are good in precision and speed when the CORDIC algorithm is used. Less hardware resources are needed.