Development of multi-channel fast SiPM readout electronics for clinical TOF PET detector

Silicon photomultipliers (SiPM) are rapidly adapted in simultaneous time of flight (TOF) PET and MRI imaging system in recent years due to its fast timing response and immunity to magnetic field. The aim of this work is to develop multi-channel fast SiPM readout electronics for clinical TOF PET detector. The detector module is assembled by directly coupling a 12×12 LYSO crystal block to an 8×8 Sensl FB30035 SiPM array. We are developing two approaches of compact readout electronics to handle the large number of SiPM output channels. One is a low noise and high bandwidth, 128-channel ASIC to readout the 64 fast outputs and 64 standard outputs of the 8×8 SiPM array. The other approach is a conventional electronics based multiplexing readout scheme using discrete components. A charge division resistor network reduced 64 channels of standard output to four energy signals, and multiplexing and summing circuits reduced 64 channels of fast output to one timing signal, making the detector block highly compact and scalable. The ASIC design has been finished and it's ready for tape-out. Preliminary performance of the detector module readout by conventional electronics was evaluated. 12×12 LYSO crystals were well resolved and identified in the flood image and the average energy resolution was 15.6% ±1.3%. For single crystal pair, 240ps coincidence resolving timing (CRT) was achieved. It was dropped down to 500ps for detector block to single crystal configuration, due to the combination effects of: 1) degradation of fast signal rising edge by output capacitance addition of SiPMs and 2)large white electronic noise and ultrahigh dark count rate. The readout design will be further optimized by increasing the signal bandwidth and reducing noise to get better timing performance at a cost of increasing circuit complexity to a reasonable level. The performance of ASIC readout will be evaluated and good timing performance is expected due to the individual pixel timing pick-off.