Research On Digital Direct Linear Phase Comparison Method Based On Dual-channel ADC

As the core content of modern cutting-edge technology,precision measurement technology has important application value in many fields.With the rapid development of satellite navigation,geodesy,aerospace and navigation technology,higher requirements are put forward for time-frequency measurement technology.Therefore,it is an urgent task to explore the method of higher measurement accuracy.Due to the influence of the internal noise of the frequency source,the output signal fluctuates randomly in frequency and phase.As an important index to measure the performance of the frequency source,the frequency stability can be divided into long-term stability,short-term stability and transient stability from the length of sampling interval.Frequency stability is generally derived from phase difference or frequency difference.Therefore,the research of frequency stability is based on the research of frequency difference or phase difference measurement method of signal.In the time-frequency measurement,the phase processing has the highest measurement resolution,while the phase processing under the analog line can maintain the original appearance of the input signal completely,but due to the shortcomings of poor anti-interference ability,strong dependence on the hardware environment,and expensive equipment,the digital measurement method has gradually gained the dominant position.However,the traditional digital measurement method still has many shortcomings,such as the need of frequency conversion and the introduction of complex electronic circuit,counter brings±1 counting error,trigger delay error and so on.In order to overcome the above shortcomings,a new digital measurement method,digital direct linear phase comparison method based on dual channel ADC,is proposed in this paper.This method uses a high stable high frequency clock source and a symmetrical dual channel ADC to cancel the influence of noise to the greatest extent,so as to achieve a higher measurement resolution.When the frequency is N times of the measured signal,the equal interval of the measured signal is divided into N parts.The areas where 0~oand 180~o are located are recorded as linear areas(0~o is located in the center of the linear area).Because there is still a small frequency difference on the basis of the frequency multiple of the measured signal,which leads to the phenomenon of small step between phases.When the clock moves out of the linear area,the next adjacent time The clock will enter the linear area,that is,the completion of the full period of a phase comparison,so that at any time,the clock sequence will fall into the linear area to complete the data acquisition in the linear section of the signal.Through the amplitude phase conversion of the linear segment data,the phase difference of the two comparison signals is derived.The resolution of measurement can be further improved by adjusting the size of linear region and selecting ADC with high quantized bits.In this paper,the basic principle and design scheme of digital direct linear phase comparison method for dual channel ADC are described in detail.The experiments of OCXO self-calibration and the comparison between OCXO and XPRO rubidium atomic clock show that the frequency stability of this method can reach E-12/s under the condition of OCXO self-calibration.This method can get the linear measurement results directly without frequency conversion with the minimum drift.At the same time,the noise index is relatively ideal,and the response time of measurement is fast and convenient Medium advantages in application to control devices.Therefore,this method has a strong competitiveness in the field of frequency standard.