Research And Implementation On Lock And Self-adaptive Hold Technique Of Oven Controlled Crystal Oscillator Based On 1pps Derived From GPS

OCXO is frequently used as clock source with high short-term stability. However, the output frequency and phase of OCXO drifts due to aging and temperature changes. When OCXO is used in a situation that needs excellent clock synchronization performance, appropriate measures must be taken to regularly tame and calibrate it. 1pps(pulse per second) signal transmitted by the GPS receiver has a very high long-term stability. So we can take advantage of this feature to calibrate OCXO and improve its long-term stability.A study on technology of OCXO tamed and adaptive holding high frequency stability based on GPS 1pps signal is presented in this thesis. GPS 1pps signal is used as a reference frequency to calibrate the output frequency of OCXO. Based on the combination of advantages of high long-term stability of 1pps signal and high short-term stability of OCXO, an excellent performance, low cost synchronous clock source is designed with its output frequency programmable(determined by the feedback divider of DPLL).Compared with the traditional OCXO tamed and hold technology, the technology presented in this thesis uses C8051F310 MCU as external processor to control the digital PLL chip AD9548. Finally OCXO is locked by GPS 1pps signal and maintain a highly stable output frequency. When the reference signal of the GPS receiver is normal, the entire system is in a closed loop state. Because of AD9548 internal DPLL loop, the long-term stability of the output frequency of the OCXO is maintained the same level with GPS 1pps. However, the output of the GPS receiver is vulnerable to external interference and be invalid. When the GPS 1pps is lost, the DPLL feedback loop will also be invalid. Any OCXO frequency drift over time and temperature changes will appear in the final output. An adaptive oscillation hold model(AOM) is established in this thesis to solve this problem. By modeling the OCXO aging drift and using Kalman filter algorithm, not only the OCXO frequency drift caused by the aging is filtered, but also the problem how to keep high stability and accuracy of the output frequency is solved when the 1pps signal is lost.Through a variety of theoretical analysis, the system hardware and software scheme are designed. On the basis of the algorithm simulation, careful debugging is made for the MCU control codes and hardware circuits. Also the test results and detailed analysis is presented. The specifications of long-term stability and accuracy of the output frequency are basically met in this project.