基于GPS的恒温晶振频率校准系统设计

发布时间：2018-04-29 19:53

  本文选题：GPS + 恒温晶振频率校准　； 参考：《中南民族大学》2015年硕士论文

【摘要】：随着信息交换的加快,频率源的重要性日益突显。频率源的不稳定会导致同步精度不够,严重情况下还可能造成系统瘫痪。目前精度较高的频率源是恒温晶振,但因其存在长期累积误差,使其难以在同步系统中得到应用。美国的全球定位系统(GPS)搭载了高稳原子钟,其输出的秒脉冲1PPS信号具有短期稳定性好的特点。因此,本文采用GPS秒信号校准恒温晶振以得到高精度频率源(称为GPS频率校准系统)。GPS频率校准系统是以FPGA数字技术作为测量手段,ARM处理器作为算法控制中心,采用锁相环频率合成技术,对晶振分频秒信号和GPS秒信号的相位进行跟踪锁定,依据两者的相位差变化量调整频率修正电压,在不破坏晶振短稳特性的基础上改善其频率的长期稳定性,以获取高稳定度、高可靠性的频率源。该系统由GPS信号接收机,高精度数字鉴相器,数据滤波和系统控制,以及晶体振荡控制等四大模块组成。其中,GPS信号接收机模块主要功能是通过放置在室外的专用接收天线接收来自GPS的秒信号1PPS;高精度数字鉴相器模块采用数字测量技术,以高速时钟计数的方法实现相位差的高分辨率测量;数据滤波和系统控制模块以误差分析和平滑控制作为设计思路,在微处理器中实现滑动平均滤波算法和自适应PID控制算法;晶体振荡控制模块采用电磁兼容性良好的低噪声DA控制电路,将处理器输出的若干比特数字量在DA电路中转化为高精度的控制电压。所研制的GPS频率校准系统在本实验室中通过长时间观测表明:晶振分频秒信号和GPS秒信号的相位差波动范围不超过65ns,实现了较好的锁相调节,且经校准后的频率精度达到了10-10量级。该系统也应用于本实验室自主研发的数字测高仪PDI-1中,成功地进行了两台仪器的斜测实验,很好地满足了斜测所需要的时间同步要求。
[Abstract]:With the acceleration of information exchange, the importance of frequency sources is becoming more and more important. The instability of the frequency source may lead to insufficient synchronization accuracy and system paralysis in serious cases. At present, the frequency source with high precision is the constant temperature crystal oscillator, but it is difficult to be applied in the synchronous system because of its long-term cumulative error. The Global Positioning system (GPS) of the United States is equipped with a high-stability atomic clock, and the output second pulse 1PPS signal is characterized by good short-term stability. Therefore, in this paper, the GPS second signal is used to calibrate the constant temperature crystal oscillator to obtain the high precision frequency source (called GPS frequency calibration system). The FPGA digital technology is used as the measuring means and arm processor is used as the algorithm control center. Using phase-locked loop frequency synthesis technology, the phase of the crystal oscillator frequency division second signal and the GPS second signal is tracked and locked, and the frequency correction voltage is adjusted according to the variation of the phase difference between the crystal oscillator and the GPS second signal. In order to obtain high stability and high reliability, the long-term stability of crystal oscillator is improved on the basis of not destroying the short-time stability of crystal oscillator. The system consists of four modules: GPS signal receiver, high precision digital phase detector, data filtering and system control, and crystal oscillation control. The main function of GPS signal receiver module is to receive 1PPS signal from GPS through special receiving antenna placed outdoors, and the high precision digital phase detector module adopts digital measurement technology. The high resolution measurement of phase difference is realized by the method of high speed clock counting, the data filter and system control module take error analysis and smooth control as the design idea, the sliding average filter algorithm and the adaptive PID control algorithm are realized in the microprocessor. A low noise DA control circuit with good electromagnetic compatibility is used in the crystal oscillation control module. Some bits of digital output of the processor are converted into high precision control voltage in DA circuit. The developed GPS frequency calibration system has been observed in our laboratory for a long time. It is shown that the phase difference between the crystal oscillator frequency division second signal and the GPS second signal fluctuates in a range of less than 65ns, and the phase locking adjustment is achieved. After calibration, the frequency accuracy reaches 10-10 orders of magnitude. The system is also applied to the digital altimeter PDI-1, which has been developed by our laboratory, and has successfully carried out the oblique test of two instruments, which meets the requirements of time synchronization for oblique measurement.
【学位授予单位】：中南民族大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P228.4
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本文编号：1821324