Design And Implementation Of Four-channel High Resolution Event Timer

As a precision instrument for measuring time and time interval,event timer is widely used in laser ranging and other fields.In this paper,a four-channel high-resolution event timer based on time-amplitude conversion method is realized.A Field Programmable Gate Array(FPGA)is used as the central processor to complete the event acquisition.In order to meet the transmission bandwidth requirements,the upper computer interface uses USB3.0.This paper first introduces the basic principle of time measurement and designs the overall scheme according to the project requirements,then introduces the hardware circuit,digital circuit module and upper computer software design of the four-channel event timer successively,and finally introduces the testing method of the timer and gives the test results.The specific work completed is as follows:Hardware design.The hardware circuit adopts modular design,which is divided into three modules: bottom plate,gusset plate and power plate.The front-end channel in the bottom plate is used to shape the input events,and the three-stage delay chain is used to separate the thickness count.Domestic ADC is used to realize 16-bit high resolution fine count data acquisition.FPGA minimum system and USB3.0 data transceiver module are integrated on the board to realize data acquisition,preprocessing and uploading.In order to compensate the measurement error caused by temperature drift,the calibration function is designed,and the analog switch is used to realize the switch between the calibration and measurement function.The gusset plate is used to convert the narrow pulse carrying time information into voltage change.The voltage to amplitude conversion circuit based on double constant current source is designed to measure the narrow pulse to improve the measurement speed and accuracy.Digital circuit module design.The channel flow state machine is designed to realize the automatic measurement of the event time.Design ADC data receiving module and plan data transmission link,control FIFO read and write to enable only effective level points to be stored.The collected quantization values of high and low levels are pre-averaged to reduce the amount of uploaded data.Finally,the USB3.0interface module is designed,and the custom transmission protocol,control word and transceiver state machine are designed to realize the data transmission between the upper computer and FPGA.Upper computer software design.This paper introduces the interface design of the application software of four-channel event timer,designs the software framework of the upper computer and writes the callback function of the control such as mode switching,waveform drawing and timer,and finally studies the input calibration algorithm and nonlinear error calculation method of the timer.Test verification.The test methods of single precision,resolution,synchronization precision,temperature drift and other indexes are given,and the relevant indexes are verified accordingly.The test results show that the single-time accuracy of the timer designed in this paper is better than 10 ps,the resolution is better than 3ps,the single-channel input drift is better than 2ps/℃,the synchronization precision between channels is better than 100 ps,and the temperature drift between channels is better than 0.5ps/℃,all of which meet the requirements of the indicators.