The Digital Phase Difference Measurement

Phase difference measurement is of great significance for the field of the measurement and control in time and frequency,and many other periodic signal parameters can be derived from it and its variation.The phase difference measurement instrument based on analog circuit has following disadvantages,such as complex structure,big noise,unstable performance,precision that is difficult to be further improved,extremely high price and so on.The method based on the traditional digital measurement uses the gate,the trigger and the counter,making the measurement circuit more complicated,debugging difficultly,and the additional drift can be involved in.Aiming at these deficiencies,a new digital method of phase difference measurement is proposed in this paper.The method is under the background of digital,through the clock cursor effect formed in phase change law between the sampling clock signal and the measured signal to implement the measurement of the phase difference.It uses the same clock signal to control two lines of ADC to sample the reference signal and the measured signal respectively,and the sampling clock frequency has some correlation with two comparison signal frequency in order to form the clock cursor phenomenon,and makes the quantitative process ordered,thus the sample point not only has amplitude information,but also has the phase information.Because the limited resolution of ADC,the quantitative fuzzy area can be formed at each quantitative number,using quantitative fuzzy area edge of to zero point to control the formation of count gate can implement the measurement of the phase difference between the measured signal and reference signal.Comparing with the analog and traditional measurement,this method not only simplifies the structure and the implementation algorithm of the measuring circuit,but also can gain the most real phase information,in addition the method uses the cursor effect to restrain the quantization error and counting error.This paper begins with the introduction of the basic knowledge involved in this measuring method,providing theoretical support for measuring scheme.On this basis,by using MCU and FPGA to develop the phase difference measurement system,and introducing the function and the specific implementation of each module in the system,some experimental verification are made at last from self-calibration experiment with the two homologous signals and comparison experiment with the signal from different frequency source.Experiments show that the method in self-calibration can make the stability reach 10^-12 a second and10^-16 a day.In addition,the drift a day is less than fifty picoseconds and will not accumulate,which is particularly suitable for the long-term comparison of high precision frequency source in stability and accuracy.Furthermore,this method will make an important contribution to the development of China's satellite navigation,positioning,timing,aerospace and other fields.It has a promising development prospect.