基于GPS同步的大地电磁采集站标定信号发生器设计与实现

THE DESIGN AND REALIZATION OF THE SIGNAL GENERATOR FOR THE CALIBRATION OF MT INSTRUMENT BASED ON FPGA AND GPS SYNCHRONIZATION

介绍一种基于FPGA与GPS同步的大地电磁采集站标定信号发生器。信号发生器在AT91RM9200控制下产生0.093 75、0.234 4、2.5、20、24 Hz共5种频率的与GPS同步的方波信号,利用方波丰富的奇次谐波一次标定多个频点。FPGA与AT91RM9200之间的通信采用自行设计的SPI接口,实现控制参数的传输。FPGA内部采用Pi-coBlaze内核作为控制核心,对控制参数进行分析处理,控制标定信号的生成和与秒信号前沿同步。合成的方波信号经光耦隔离后接入模拟通道电路。测试结果表明,GPS同步标定信号发生器能够正常工作,标定信号输出滞后PPS秒信号前沿小于1.5μs,带宽不低于10 MHz,幅值稳定,满足标定要求。

In this paper,a FPGA-based GPS synchronous signal generator for the calibration of MT instrument is presented.Under the control of AT91RM9200 processor,five square wave signals with specific frequencies of 0.09375,0.2344,2.5,20 Hz and 24 Hz for calibration can be generated,and are synced with GPS＇s PPS.Multiple frequencies calibration is all done at the same time due to the nature of square wave composed of extensive odd harmonics.We designed a SPI interface to realize the communication between FPGA and AT91RM9200.The soft IP processor PicoBlaze,as the control center inside FPGA,is employed to analyze and process the control parameters,and to control the synthesis of frequencies and their synchronization to the rising edge of PPS.The synthesized square signal is transmitted to the analog channel board through photon-coupled isolator.As the test result proves,the signal generator works well,and calibration signals have a lag of less than 1.5μs to the rising edge of PPS,more-than-10 MHz bandwidth and stable amplitude,which meets the calibration requirement.