In the operation,the frequency source will inevitably be affected by temperature effects,environmental noise,aging of components,etc,which causes frequency drift of output signals,accuracy decrease,and signals not synchronized.Although the errors caused by these phenomena are small,they can seriously affect the performance of frequency sources in the field of high-precision measurement,which cannot be ignored.Therefore,in order to meet high-precision measurement,improving the accuracy of the frequency source is an inevitable choice for the development of the times.The frequency source has two processing methods:phase processing and frequency processing.Among them,phase processing has higher measurement accuracy than frequency processing,and its frequency stability varies 1/τ with sampling time.However,because the current understanding of phase and phase difference is limited and the phase processing structure is complex,the frequency processing based control method is the most widely used method in current frequency sources.However,the traditional frequency processing method can only process the same frequency signal,and the different frequency signal needs to be normalized by some complicated frequency conversion circuit.In this process,a large amount of noise mainly based on frequency-modulated white noise is introduced,which seriously affects the frequency stability of the frequency source.In this mode,the frequency stability of the frequency source varies 1/(?)with sampling time,and the processing accuracy is low.In order to improve the low precision of traditional frequency processing,this paper designs a new high-precision digital frequency processing measurement system.The system determines the virtual gate based on phase synchronization.It combines conventional adjustment and precision adjustment to control the VCXO in real time for high-precision measurement.In the measurement system,the analog signal is directly converted into a digital signal,which avoids the introduction of the frequency conversion circuit,and ensures that the measured signal can acquire phase information continuously without loss.By using the feature of high precision and high resolution at the quantization edge compared to other positions,the edge at the phase synchronization between signals is effectively extracted and used as the flag of the gate,which minimizes the quantization error.The system uses two adjustments:normal adjustment and precision adjustment,which can the quick adjustment and complete fine adjustment after locking,making VCXO precise adjustment and control.Based on the digital frequency processing,the system measures the frequency stability of the frequency source and the corresponding phase noise under self-calibration and mutual ratio.The system comprehensively analyzes the noise before and after the system processing and the change of the corresponding frequency stability curve according to the time-frequency domain correspondence of frequency stability.The analysis results reveal that the system uses frequency processing to improve the essence of frequency stability,that is,the frequency modulation white noise introduced by the frequency processing is suppressed,the phase modulation noise plays a leading role,and the frequency stability will change from 1/(?)to 1/τ.In addition,the measured signals are set to different deviations,and the variation law of the frequency stability is measured.According to the experimental data,it is found that the frequency of the measured signal varies under different deviations.Theoretical analysis shows that the finer the step value between signals,the better the phase synchronization accuracy,and the phase noise introduced by the digital frequency processing will change accordingly,resulting in the frequency stability also changing.In the new digital frequency processing mode,the frequency stability of the frequency source is changed from 1/(?)to 1/τ,achieving high-precision,high-resolution measurement.Moreover,the measurement system has a simple structure and low cost.This has greatly promoted the development of China’s high-precision measurement core technology,navigation and aerospace industry. |