| Frequency stability is a representation of the phase noise in the time domain,at the same time it is one of the indispensable index of a standard source quality,it is also an important part in the filed of time and frequency measurement and control.Frequency stability can be divided by the length of the response time of transient frequency stability,short-term frequency stability and frequency stability for a long time.It is generally derived by the frequency or phase,therefore,the measure of it is the study of the measurement of frequency or phase difference.The traditional methods of frequency and phase difference measurement are generally in a simulated environment,although can reach a certain precision,there are some problems,such as a single point of zero passage detection is very sensitive to noise and the requirements of circuit performance is very strict and so on,which restricts the improvement of the accuracy of measurement.In addition,traditional methods are based on the basic of the gate count,with the decrease of the measuring gate,the precision can be lower,therefore,the length of the measuringgate can not be too short,which makes it difficult to measure the transient frequency stability of the signal.In view of these shortcomings,this paper extends edge effect to digital field,and proposes a full response time frequency stability measurement method.Under the digital background,the clock cursor effect and the digital edge effect are applied to the measurement,and the frequency stability of the full response time of different frequency sources is realized with the digital phase recognition algorithm.The method uses two analog-to-digital converter to sample the measured signal and the reference signal respectively,and use clock cursor effect to control ADC sampling process,which makes the digital output analog-to-digital converter retain the instantaneous phase of the original,and form the digital fuzzy region.Thus the instantaneous phase of the signal is extracted by the digital phase discrimination algorithm,and the instantaneous phase difference between the signals is obtained,and the transient frequency stability is calculated.At the same time,the clock cursor effect and digital edge effect are combined to inhibit quantization error existing in analog-digital converter,and the phase difference between signals is obtained by digital phase discrimination algorithm,and the frequency stability of short and long term is obtained,so the frequency stability of full response time is measured.This paper introduces in detail the clock cursor effect,digital edge effect and digital frequency stability measurement principle and basic theory,the design and implementation of digital frequency stability measurement system,and the hardware and software of measurement system.On the basis of the measurement system,the OCXO self calibration experiment and the comparison experiments of different frequency sources are carried out.The experimental results show that in the self-calibration experiments,its transient stability can reach 10-5/100ns,short-term frequency stability can reach 10-12/s,and long-term frequency stability can reach 10-16/day,realizing the frequency stability measurement of the full response time of different frequency sources,and reveals the variation of frequency stability with time in essence. |
