Research And Application Of The Precise Time Resolution TDC Based On FPGA

Time measurement technology has been widely researched and applied in nuclear physics experiments,large scientific devices,digital communications,aerospace,navigation and positioning.In the recent years,various kinds of time measurement technology has developed,such as the original analog circuit consisted of discrete components,the use of special time interval measurement chips as well as the research of time and digital conversion circuit based on FPGA.The time resolution has become much better,and the measuring way is more flexible which can meet the requirements of most kinds of physical experiments and engineering applications.In order to measure and study the secondary charged cosmic rays,a small cosmic ray detector was designed and constructed by the Institute of modern physics,Chinese Academy of Sciences.The device is used to measure the arrival time of shower particles with a high time accuracy,so as to obtain a better resolution of cosmic ray incident angle.Meanwhile,the time of leading/trailing edge of particle pulse is measured to get the energy loss and decay time of particles in sensitive detector.The cosmic ray experiment requires a time resolution less than 500 ps,and the measurement of coincidence of particle events and the time over threshold are completed in a single pulse event.Time measurement circuit with discrete components can achieve high time resolution,but it is difficult to carry out a coincidence measurement.And the use of ASIC chips will lead to high cost,which is not convenient for the promotion of the detection device.The researchers in Heavy Ion Research Facility in Lanzhou(HIRFL)introduced a Barrier Bucket beam extraction and injection method in the design of kicker control system between two ring accelerators.This kind of beam injection/extraction mode must be strictly depended on the extraction phase of the beam extraction loop(BRing)and the injection phase of the beam receiving loop(SRing).The arbitrary phases of the two rings' frequencies are adopted to make a coincidence with a phase jitter less than 1 degree,and the accuracy of time delay for timing control in the Kicker magnet power supply should be better than 1ns.In this paper,the principle of high precision time to digital conversion circuit(TDC)based on FPGA were studied and a multi-channel TDC was implemented on a low cost Cyclone IV series FPGA to meet the above requirements of physical experiments and engineering applications.The accuracy of time measurement is up to 45 ps and a realtime coincidence and decay time measurement system for particle pulse events was also built in FPGA.At the same time,the FPGA-TDC technology was used to complete the double loop high frequency phase time measurement and coincidence with a subnanosecond accuracy.The high precision time delay control with step time of 90 ps was completed.