Accepted: 2025-07-23
Frequency standards play a vital role in modern science and technology and industry, in view of the problem of poor long-term stability of the constant temperature crystal oscillator affected by crystal aging and temperature and other factors, a constant temperature crystal oscillator frequency locking system based on phase-locked loop structure is designed, with the GPS signal received by the u-blox NEO-M8N module as the reference source, and the single-chip microcomputer STM32F103C8T6 as the control chip, and the frequency of the constant temperature crystal oscillator OC5SC25 is locked through the phase-locked loop structure. Using the extended Kalman filter and PID control algorithm, the long-term stability of the primary frequency standard and the short-term frequency accuracy of the secondary frequency standard are combined, and the test results show that the system realizes the frequency lock of the 10MHz constant temperature crystal oscillator, which can lock the frequency of the constant temperature crystal oscillator to a higher stability and accuracy. Its average frequency accuracy reaches 3.28×10^(-12), which is nearly 4 orders of magnitude higher than the initial frequency accuracy, which effectively improves the limitations of the constant temperature crystal oscillator in long-term stability.