Research On Zero Dead Time Frequency Measurement Method Based On Multi Period Synchronization

It is one of the seven basic physical quantities in the international time unit system,with the highest measurement accuracy.The measurement of other physical quantities can be traced back to time.Frequency is essentially the same quantity as time,so time-frequency technology plays an extremely important role in the field of measurement and testing.Due to the problems of zero dead time and slow signal processing in traditional measurement methods,it is impossible to identify the frequency hopping of enemy radio stations with high accuracy in electronic countermeasures;When studying the change of Doppler frequency,it is impossible to continuously observe the frequency;Usually when an oscilloscope is used;the key accidental signal will also be lost.Therefore,it is of great application value to study the frequency measurement method zero dead time.This thesis begins with the traditional frequency measurement methods such as the phase contrast method,the analog interpolation method and the double-hybrid time difference method,then analyzes and compares the basic principles and frameworks of several methods,as well as their respective advantages and disadvantages in detail,a frequency measurement method zero dead time based on multi-period synchronization is proposed.By accurately detecting the edge of the least common multiple periodic signal of the measured signal and the reference signal as the front and rear edges of the gate signal in actual frequency measurement,the synchronization of the measured signal,the reference signal and the gate signal is realized.which not only eliminates the±1 error in the counting process of the traditional multi-cycle synchronous measurement method,but also realizes the sampling of the phase information between two sampling periods of the measured signal zero dead time,and achieves the same resolution measurement in a wider frequency range.The hardware circuit of frequency measurement system zero dead time based on multi-cycle synchronization is divided into five sub-modules according to their functions,including signal conversion module,DDS module,pulse extraction module,signal synchronization module and power supply module.In the process of signal processing,the response time of signal processing is reduced,the processing speed is improved,and the anti-interference ability is enhanced by using the characteristics of fast ECL level processing and small swing of logic level.The power supply module is a self-designed linear power supply,which has the characteristics of small output voltage fluctuation,fast transient response and good stability,and reduces the electromagnetic interference of the power supply module.The software part of this system mainly completes the preliminary measurement algorithm for the measured signal,and controls the DDS module to generate a reference signal;in the process of communicating with the FPGA,it cooperates with the pulse extraction module and the signal synchronization module to complete the extraction of the count value of the measured signal and the reference signal from the FPGA to achieve high precision measurement of the measured signal.This design concept gives full play to the advantages of the simple MCU development process and the high concurrency and low latency of the FPGA,which ensures the reliability of the system and the integrity of the data.The overall scheme is tested several times,the self-calibration experiment and the mutual comparison experiment of the system are completed,and the main factors that cause the error of the system are comprehensively analyzed,corresponding optimization measures are proposed eventually.After experimental verification,the measurement stability at the second-level of the measurement scheme can reach the order of 10^-13/s,and the measurement method has the characteristics of system stability,simple structure and low background noise,it realizes the zero dead time measurement of the measured signal.The measurement has a certain reference significance for the use of multi-period synchronous measurement in the field of time-frequency measurement.It is planned to carry out a more complete design of the PCB layout later,isolate and shield the components that are susceptible to interference,further enhance the anti-interference ability of the system,and consider adding a precision temperature control module to improve the overall temperature characteristics of the system thereby improving the measurement accuracy of the system in a better way.