FPGA based fast integrated real-time multi coincidence counter using a time-to-digital converter

Abstract

The precise measurement of time is very important in many engineering and science applications. In some of the applications the time measurement is used to investigate the correlation between the timing of events and coincidence counters are employed for this purpose. Coincidence counters are commonly used as instruments in applications such as gamma ray correlation in positron emission tomography(PET) and gating events of interest from background noise in quantum physics experiments. In order to implement coincidence counters, time-to-digital converters can be used. While providing precise measurement, it is also important to maintain real-time operation and fast data processing due to the change in interest of events during the application. In this research, we have developed a real time multi-coincidence counting scheme in a Field Programming Gate Array (FPGA) based on our 8-channel time-to-digital converter(TDC) which we have published. With this method we have managed to combine an 8 channel TDC with a coincidence counter in the same FPGA chip while providing real-time operation and high precision. The smallest coincidence window, our system can provide is 15 ps and at 150 ps our system is capable of detecting the maximum number of coincidences. Also, the functionality of the coincidence counter has been proved by tests of coincidence rate as a function of window size and coincidence rate as a function of delay.