Research On High Precision Time And Frequency Measurement Technology Based On Multi-group TDC

High precision time and frequency have gradually become important parameters of a nation’s comprehensive strength.In many fields such as scientific research,engineering application,production and life,high precision time interval and frequency measurement were widely used.The importance of high precision time frequency measurement technology in the field of precision measurement is particularly prominent: for example,the distance accuracy of laser ranging depends on the measurement accuracy of time interval,the realization of positioning system in satellite navigation is also based on the measurement of time difference,and the accuracy of frequency signal measurement will also determine the accuracy of the magnetometer for magnetic field.Since many physical quantities such as temperature,capacitance,distance can be transformed into time and frequency measurement,improving the accuracy of time and frequency measurement will indirectly improve the measurement accuracy of the above physical quantities.Therefore,many fields put forward higher and higher demands for time and frequency measurement.With the development of science and technology,many fields are not only satisfied with the high accuracy of time and frequency measurement,but also put forward further requirements for multiple parameters such as the measurement range of time and frequency signals,the presence or absence of dead-time of measurement,and nonlinear errors.When the quantization delay method based on TDC(Time to Digital Converter)chip is used alone,or the pulse filling method based on FPGA(Field-Programmable Gate Array)chip is used for time and frequency measurement,both are difficult to meet the corresponding indicators.Based on the FPGA chip and multiple sets of TDC-GP21 chips,this paper has designed and completed the development of a time and frequency measurement module without dead-time.The main research contents and results are as follows:Using the method of "corase time" + "fine time",the " corase time" measurement was realized through FPGA,and the "fine time" measurement with high-resolution was realized based on the dedicated TDC measurement units.Considering the relationship between the number of TDC chips in the TDC measurement unit and the measurement accuracy,as well as the development cost of the equipment,three TDC chips were used to form a group of TDC measurement units.The three TDC chips in the TDC measurement unit were used to measure the "fine time" in the time interval,and the average filtering method was adopted to process the measurement results of the three to output.Compared with using a single TDC chip,the measurement resolution was increased from 22 ps to 13 ps.The time measurement module composed of the above two sets of TDC measurement units and FPGA chip(including 32-bit counter)alternately measured the target frequency signal,thus achieving frequency measurement without dead-time.The software system of the designed time and frequency measurement equipment in this paper mainly includes two parts: the lower computer with STM32 as the core and the upper computer software based on the Visual Studio environment.The hardware system is mainly composed of three parts: power module,core measurement module and temperature control module.The time and frequency measurement module based on multiple TDCs developed in this paper was better than the time interval counter SR620 of American Stanford,which is widely commercialized.The stability of frequency measurement was better than the universal time and frequency counter 53230 A with dead-time that belongs to Keysight Technologies,and was equivalent to the K&K FXE,which is a frequency device without dead-time produced in Germany,also can replace them for frequency signal measurement.