Research On Adaptive Bandwidth Phase Locked Loop Clock Taming Technology Based On TDC

Constant temperature crystal oscillator has good short-term stability and low cost,but long-term stability is affected by temperature and aging rate,and GPS(Global Positioning System)1PPS(Pulse Per Second)has good long-term accuracy and stability,in order to combine the advantages of the two,this paper studies a an adaptive bandwidth phase-locked loop clock taming technique based on TDC(Time-to-Digital Converter),which not only solves the problem of poor accuracy of local crystal oscillators for a long time,but also solves the problem of GPS 1PPS taming local crystal oscillators for too long locking time through digital phase-locked loop bandwidth adaptive algorithms,and its main research content is as follows:(1)The TDC module based on FPGA(Field Programmable Gate Array)is designed to measure the time difference between the 1PPS signal of GPS and the rising edge of the 1PPS signal of the local crystal crossover,the measurement resolution of the TDC module can reach 13.25ps,the jitter range of the measurement result is about±80ps,and the dynamic range of the measurement can reach the second level.(2)A digital phase-locked loop bandwidth adaptive algorithm and temperature compensation algorithm based on a priori measured parameters are proposed,which improves the locking speed,expands the phase-locked loop bandwidth,and reduces the influence of frequency offset caused by crystal oscillator temperature change on taming accuracy.The prior measured data is used to establish a priori measured model of the reference input signal and loop bandwidth parameters,which is used to provide bandwidth parameters suitable for the current reference input.Then,the measured frequency difference data is substituted into the model,which can further adjust the bandwidth parameters with the frequency difference input of the model,improve the bandwidth parameters suitable for the current reference input.Then,the measured frequency difference data is substituted into the model,which can further adjust the bandwidth parameters with the frequency difference input of the model,improve the loop lock range,and reduce the loop lock time.The temperature frequency change experiment was carried out on the constant temperature crystal oscillator,and the relationship between the frequency and temperature change was obtained,and the frequency and temperature characteristic model of the constant temperature crystal oscillator was established,and the temperature compensation algorithm was designed by this model to reduce the frequency drift influence caused by the temperature change of the constant temperature crystal oscillator.(3)The experimental data of double DAC(Digital to Analog Converter)frequency control are analyzed,the output characteristics of dual DAC are obtained,and the adjustment model of frequency difference and dual DAC frequency control word is established,which realizes the conversion of digital control quantity to analog control quantity,so as to realize the accurate taming of local crystal oscillator.The 1PPS signal of the local crystal oscillator is obtained by the frequency division of the frequency division module,which is used to compare with the time difference of the GPS 1PPS signal.Through the study of the above content and the verification of experimental results,the long-term accuracy of the output frequency of the local precision 10-7 magnitude crystal oscillator after taming can reach the order of 10-10,which can be applied to scenarios with high precision and low cost requirements for time-frequency signals.