Design And Research Of Frequency Calibration System Based On Beidou Pulse Per Second

With the rapid development of society,economy and technology,people have increasingly higher requirements on the accuracy of time and frequency.High-precision time-frequency reference and synchronization have become an indispensable part in the fields of communications,power,defense and aerospace.The Satellite Navigation System is currently the most mature timefrequency system.Beidou Satellite Navigation System will achieve global coverage in 2020.The study used the Beidou timing to complete the local frequency reference correction,forming a low-cost,high-accuracy,good stability local frequency reference source,which has great application value.The thesis designs and studies a frequency calibration system that uses the Beidou timing 1 Pulse Per Second signal to correct the output frequency of the local Oven Controlled Crystal Oscillator.By designing a high-resolution Time-to-Digital Converter to measure the time interval of the satellite 1PPS that has been monitored for effectiveness and the local 1PPS output after coarse synchronization of the frequency divider.In order to suppress the 1PPS front-end jitter and the random noise of the system,coarse value culling and Kalman filtering algorithm are used to process the time interval data to reduce the impact of noise.At the same time,an adaptive hold algorithm is proposed when the satellite loses lock without a reference datums to ensure the normal operation of the frequency calibration system.Finally,the PID control algorithm is applied to improve the correction tracking effect of the frequency calibration system,and after the correction amount calculation is completed,the high-precision Digital-to-Analog Converter is driven to convert it into an analog voltage signal to correct the output frequency of OCXO.In the thesis,The measurement resolution of tapped delay line TDC based on CARRY4 can reach 91ps.Relative pulse counting nanosecond accuracy effectively improves the measurement accuracy of the frequency calibration system.The system function module is constructed through the IP core and uses the AXI bus to communicate with the integrated ARM processor,which greatly improves the system integration.The design optimized Kalman and PID joint estimation control algorithm has better filtering control effect.The frequency calibration system keeps OCXO and satellite reference synchronized to a certain degree.It has certain theoretical and application value.