Research On Digital Phase Measurement And Control Technology Of Different Frequency Signals

With the development of technology,more and more fields require more accurate time reference and clock synchronization.In the field of time-frequency measurement,phase comparison is an important way to achieve high-resolution and high-precision frequency standard comparison.At present,the phase comparison and locking of signals between different nominal frequencies usually need to be normalized to the same frequency signal.Therefore,the method proposed in this thesis to achieve direct phase comparison and locking between different frequency signals is of great significance.In this thesis,the digital measurement technology is introduced in the phase comparison process,and the direct phase comparison between different frequency signals is realized by using a single analog-to-digital converter(ADC).In order to solve the measurement dead zone caused by the non-linearity at the peak of the measured signal in the digital measurement process,the phase interval [-π/20,π/20] with good linearity of the measured signal is selected as the phase comparison linear zone,and the change rule of phase difference between two different frequency signals is analyzed.The conclusion is that there is no obvious change rule in the phase difference within the least common multiple period of the two compared signals,but taking the least common multiple period as the overall analysis,there is a continuous change process of phase difference within a phase group period.On the basis of this conclusion,ADC is used to directly compare the phase of the two compared signals.The time information of the phase difference in the linear region and the adjacent two linear regions are collected and stored.After data processing,the highresolution measurement of frequency stability is realized.On the basis of realizing the direct phase comparison of the different frequency signals,the frequency division link in the traditional PLL system is eliminated,and the direct locking between the different frequency signals is completed in this thesis.The voltage linear region obtained from the phase linear region of the measured signal is processed by the limiting amplifier circuit to the full range of the ADC,and the ADC directly completes the digital phase discrimination between thedifferent frequency signals.After the phase detection results are transmitted to singlechip STM32,average filtering is performed on the data to reduce the jitter error caused by the source noise.According to the voltage control sensitivity of the selected crystal oscillator,the parameter design of the PI algorithm is adjusted,and the Digital to analog converter(DAC)output voltage is controlled to lock the crystal oscillator to improve the frequency stability of the measured signal source.The performance of the phase comparison and locking system is evaluated by experiments.The experimental results show that,the frequency stability of 1μs can reach 2.21E-07,and the frequency stability of 1ms can reach 2.12E-10 with constant temperature oscillator OCXO8607 as the self-calibration signal source.The 5MHz signal output from the constant temperature crystal oscillator OCXO-0285,the measured signal source is locked by a 7MHz signal generated by signal generator which uses OCXO8607 as reference.After locking,the second-level frequency stability is improved from 6.06E-11 in the open loop to 2.95E-12.In this thesis,no frequency normalization is needed in the process of system design,and the digital direct phase comparison and locking between different frequency signals are realized.