Design And Realization Of High-stability Signal Source Based On GPS

As the core component of electronic system, the accuracy and stability of signalsource directly determines system performance. In order to meet the accuracy andstability demands of synchronous work between remote devices, a high-stability signalsource based on GPS is designed in this paper.The common frequency source are LC oscillator, crystal oscillator, atomic clockand so on. The frequency of LC oscillator is adjusted conveniently, but easy affected bytemperature. The stability of hydrogen clock and caesium clock are better than1×10-13，but they are expensive. The stability of OCXO （oven controlled crystal oscillator） isover1×10-7with high cost performance. The system selects the good temperaturestability OCXO as the local frequency source to meet the need of design index.The aging of OCXO will lead to long-term frequency drift. A phase-locked loop（PLL） is designed to regulate the frequency of OCXO. The main idea behind is to usethe1PPS signal, which comes from GPS receiver, as a reference to calibrate the OCXOby integrating the long-term stability, excellent tracking and holding characteristic ofGPS and the short-term accuracy of OCXO. The time interval is precisely measured bypulse counting method and quantized time-delay method, which reduce calibration error.To eliminate the disturbance of the1PPS jitter, moving-average filter is used to processtime-interval measurement data. In the early running time of the system, a quickfrequency calibration process is added to make crystal frequency error rapidly intocapture bandwidth, and reducing the time of crystal reaches to locked state.In addition, in the application area of requiring wide frequency range, OCXO onlyoutput a single frequency, which cannot meet the need of signal source wide frequencyrange output. The system adopts GPS tame technology, combine with direct digitalfrequency synthesis （DDS） which has a wide frequency range characteristics. Thefrequency can be output with high stability and adjusted in wide range.After testing the signal system that we research by ourselves, the results indicatethat the OCXO can be quickly locked in the high-accuracy frequency. Long-termfrequency accuracy is better than7×10^-10and frequency drift is effectively restrained. The relative stability of two different signal source is good, long-term stability is higherthan9.8×10^-11. It can output adjustable frequency signal between1²50MHz.Moreover, it also outputs time message which has10ns time unit.