Research And Design Of Digital Linear Phase Comparison Method

The importance of accurate time frequency for the construction of a modern country is self-evident.With the continuous development of high-precision frequency standard sources,high-precision frequency standard comparison technology also needs to be continuously improved.At present,most frequency standard comparison techniques are through frequency processing,and phase processing has an advantage in accuracy compared to frequency processing.Hence it becomes very meaningful to propose a high-resolution digital linear phase comparison technique.In this thesis,by studying the phase change between the periodic signals of arbitrary frequencies,especially the periodic signals whose nominal frequencies constitute a multiple relation,it is found that the above phase comparison is equivalent compared with that between the periodic signals with the same nominal frequency.Besides,because of the smaller quantified phase shift resolution,a higher measurement resolution can be obtained.In this thesis,the high-speed analog-to-digital converter is used as the phase detector to control the comparison happening in the linear region of the measured signal,which realizes the extraction of high-precision,digital,and high-linearity phase difference information and avoids the dead zone phenomenon in the usual phase comparison.And the reference signal is multiplied to ten times the nominal value of the measured signal frequency and then used as the clock signal of the high-speed ADC to sample the measured signal,so as to ensure that there is always one of the ten consecutive clock signals collecting the linear region of the measured signal.It is guaranteed that all clock signals can be intermittently scanned in the linear region of the signal.And the interval between clocks is exactly one-tenth of the comparison signal period.In this way,the full period of the obtained linear phase alignment is exactly equal to the period of the higher frequency clock signal,and the obtained linearity is only equal to the optimal linearity of the sinusoidal signal waveform near zero degrees.This thesis studies the principle of linear phase comparison between sinusoidal signals with different frequency relationships.A digital linear phase comparison system with multiple frequency relationships is designed and implemented.Based on this system,self-calibration experiments and comparison experiments are implemented.It is showed that in the case of self-calibration the transient frequency stability of this method can reach σy(100ns)=2.42X10-6,the short-term frequency stability can reach σy(1s)1.71 ×10-13,and the long-term frequency stability can reach σy(10000s)=2.92×10-17.In the comparison experiments,the frequency stability curves of the rubidium clock and the cesium clock change with the average time along the law of 1/τ in the short-term,and then change between 1/τ and(?),and finally change along the law of(?).The method has a simple structure,convenient measurement,and can realize the measurement of frequency stability from transient period to long-term,which has a certain role in promoting the development of the time-frequency field.