基于FPGA的恒温晶振频率校准系统的设计

The design of frequency calibration system for OCXO based on FPGA

为满足三维大地电磁勘探技术对多个采集站的同步需求,基于FPGA设计了一种晶振频率校准系统。系统可以调节各采集站的恒温压控晶体振荡器同步于GPS,从而使晶振能够输出高准确度和稳定度的同步信号。系统中使用FPGA设计了高分辨率的时间间隔测量单元,达到0.121 ns的测量分辨率,能对晶振分频信号与GPS秒脉冲信号的时间间隔进行高精度测量,缩短了频率校准时间。同时在FPGA内部使用PicoBlaze嵌入式软核处理器监控系统状态,并配合滑动平均滤波法对测量得到的时间间隔数据实时处理,有效地抑制了GPS秒脉冲波动对频率校准的影响。

In order to meet the demands of synchronization between signal acquisition stations in the three-dimensional magnetotelluric exploration technology, this paper designs an OCXO frequency calibration system for acquisition stations, which can be used to synchronize the OCXO in each acquisition station to GPS system with high accuracy and stability. We use FPGA to design a high resolution time interval measurement unit achieving 0. 121 ns resolution, which can measure the time interval between the OCXO and GPS with a high precision and enhance the system working efficiency. In addition, soft IP processor PicoBlaze is em- ployed to supervise the system status and coordinates with moving-average filtering algorithm to filter the fluctuation in measurement data, which can effectively suppress the fluctuation of 1-pps.