广域电磁法接收机数字信号FFT实时实现技术

针对广域电磁法（WFEM）接收机各频组数字信号快速傅里叶变换（FFT）点数不统一、低频组点数大不适合现场可编程门阵列（FPGA）实时实现的技术难题，本文采用插值和抽取相结合的抽样率转换方法，提出了满足广域电磁法接收机要求的等长度FFT变换技术，将各频组FFT变换点数统一变换到1024点，并以广域电磁法接收机实际采集到的电场信号进行了测试，最终在EP2C35F484C8 FPGA芯片上实现了1024点FFT变换，最高响应频率达到了93.84 MHz，完成1024点广域电磁信号FFT运算最快只需34 μs，并且能够有效提取广域电磁信号的振幅和相位信息.结果表明：在对广域电磁法接收机信号进行FIR低通滤波后，能够通过插值和抽取相结合的方法，将各个频组FFT变换的长度统一变换成1024点，实现广域电磁信号的FFT实时变换.本文提出的等长度FFT变换技术能够满足新一代高性能广域电磁法接收机FFT实时变换的需求.

Real time implementation of digital signal FFT transform in the receiver of the WFEM

Considering the characteristics of electromagnetic field signals from the receiver of the Wide-Field Electromagnetic Method (WFEM) receiver, using the pumping and extraction I/D rational sampling rate conversion technology, this work proposed an equal length Fast Fourier Transform (FFT) conversion technology to improve this receiver, in which FFT points of each frequency group can all be transformed into 1024 points. Then the field signals from this receiver were tested and demonstrated. Next, a 1024-point FFT was implemented on the EP2C35F484C8 Field Programmable Gate Array(FPGA)chip. Results show that the highest response frequency reaches 93.84 MHz, the FFT operation of 1024-point wide-area electromagnetic signal can be completed in only 34 microseconds, and the amplitude and phase information of the wide-area electromagnetic signal can be effectively extracted. It means that after FIR low-pass filtering, FFT transformation points of all frequency group in the receiver can be well transformed into 1024 points by using interpolation and decimation methods, which solves the key technical problem that the FFT transform lengths of each frequency group is not unified and not suitable for FPGA implementation in the wide-field electromagnetic method. Finally, using Altera Company FFT IP core, a 1024-point FFT transform was implemented and tested. Results show that the proposed equal length FFT conversion technology can be fully meet the technical requirements of real-time FFT implementation in the new generation receiver of the WFEM.