Digital Phase Comparison Technology And Its Application In The Reconstruction Of Atomic Clock

Phase difference measurement technology is widely applied in information superhighway,space rocket launch,GPS navigation and satellite positioning,self-driving,aircraft take-off and other practical engineering technology in the transportation industry.With the development of artificial intelligence,various industries have gradually strict requirements on time synchronization technology.Researchers in China and overseas began to devote themselves to the research of phase difference measurement and frequency correction technology for high-precision frequency sources.They constantly reduce noise by reducing analog frequency conversion circuit,sampling dual-channel symmetry mode,amplifying phase of public oscillator and other methods,but the accuracy and resolution cannot be further improved due to the limitations of the devices and methods.In recent years,digital technology has become the main research direction of global researchers by virtue of its strong portability,integration and low cost.Therefore,for the two signals with low resolution,limited accuracy and difficult to correct dynamically changing with time in the existing frequency correctors,this paper proposed a high-precision dynamic phase difference measurement and frequency correction technology,which is mainly as follows:1)In terms of reducing measurement error and improving measurement resolution and efficiency,this paper,by analyzing the complexity of the measurement system caused by the huge data calculation during ADC analog-to-digital conversion,studied the frequency law of arbitrary comparison signals.It is found that the phase difference of two comparison signals changes periodically with the minimum common multiple period as the minimum unit.Therefore,the edge effect method is used in the design to sample and extract the effective data in the linear region of the comparison signals,so as to reduce the large amount of invalid work when the sine function performs the voltage phase conversion.2)In order to solve the shortcoming of the measurement of the short-term stability of the existing instruments,the research combined with the full digital equipment to realize the measurement of the phase difference between two different frequency signals that change with time.By using Quartus II software and Verilog HDL hardware development language,the effective data are collected,extracted,stored and preprocessed,and the software simulation is carried out,realizing the rapid processing of a large amount of data produced by ADC in a short time.3)In the application of frequency correction and stability measurement,an adjustable numerical control voltage is given to the VCXO through the conversion relationship between phase and frequency,combined with the single-chip microcomputer and output of low-pass filter.Precision frequency adjustment is carried out by the combination of coarse tuning and fine tuning under closed loop condition.After the design is completed,the simulation circuit is transplanted to the hardware device.The frequency stability of the system was measured and the results were analyzed through self-calibration experiment and cross-comparison experiment,and the maximum phase difference error between the measured signal at zero point and the reference signal was calculated,then the final resolution of the phase difference measurement system was obtained.The experimental results showed that this scheme can realize the phase difference measurement and frequency correction of two comparison signals in which the frequencies are multiples of each other and there is a small frequency difference.In the self-study experiment,The phase comparison frequency stability can reach the magnitude of 10^-12at 1s,reach the magnitude of 10^-14at 100s and the resolution reach the magnitude of 1.5ps,with the characteristics of low noise,high resolution,high stability and high adjustability.