Research And Design Of Ultra-high Precision Frequency Meter

The frequency is one of the characteristics of the electrical signal.Compared with the amplitude,average current or voltage,its measurement value is the simplest and the most accurate.Therefore,the physical value of many high-precision sensors is based on the principle of converting the measurement value to the frequency value.However,the traditional frequency measurement methods,such as the direct counting method,are difficult to meet the requirements of the acquisition speed and acquisition accuracy in the frequency measurement technology of atomic magnetometers.The purpose of this thesis is to design a frequency meter for the acquisition of frequency signal output from a high-sensitivity scalar atomic magnetometer.The measurement frequency range is approximately 70kHz to 350kHz with a resolution better than 0.35mHz.At the same time,it can guarantee an ideal rate of data update.The scheme is based on the measuring period method,which uses the principle of time-interpolation to divide the time interval measurement into two processes:coarse measurement and fine measurement.The system uses STM32 as the control center of the entire circuit to complete functions such as TDC register configuration,data processing,SPI communication,and LCD display.The FPGA is used to provide the hit signal that triggers the start/stop measurement of the TDC,and to make the coarse count within the threshold time,which expands the time measurement range.And the TDC is used to measure the time deviation existing in the two ends to eliminate the ±1 reference signal counting error.The thesis,first of all,describes the application background of the high resolution frequency measurement system and the development of modern frequency measurement technology;then introduces a variety of time-frequency measurement methods,analysis of their respective advantages and disadvantages,and takes the TDC-GP22 as an example;finally,gives the hardware design idea and software implementation method.Two measurement schemes are described in detail and the improved one solves the problem of the "dead time" that exists in TDC.The result shows that the design is feasible and there is a possibility of further improvement.