An FPGA-based 64-channel DAQ system using linear time-over-threshold scheme for a continuous crystal PET detector

We have proposed a novel practical nuclear pulse digitizing method, called linear TOT scheme, which linearly converts the peak amplitude of pulses into the time-over-dynamic-threshold (TODT) to realize the digitization by a TDC. In this paper, we are presenting a prototype design of an FPGA based 64-channel DAQ system for a continuous crystal PET detector using the linear TOT scheme. The system mainly consists of 64-channel active RC integration and comparison circuits, a shared time-varying threshold voltage generation circuit and an FPGA. The physical size of the system is so compact that it could be attached on the base of the PMT. The preliminary test result shows that the system could achieve even better performance than the DAQ system designed by normal ADC technique in our previous work. The design proves that the linear TOT scheme is very effective solution for a high channel count digitizing system in nuclear detection, not only for its high performance and low cost, but also for its high degree of integration.