Research On The Readout Electronics Of Silicon Photomultiplier Array For TOF-PET Application

Time-of-flight PET(TOF-PET)is an advance over traditional PET by achieving better image quality.Silicon photomultiplier(SiPM)is a recently developed photon detection divice,which is promising to replace photomultiplier tube in(TOF-)PET detectors.However,SiPM array requires high density and high performance readout electronics.This dissertation studied the readout electronics of SiPM array for(TOF-)PET application.Since presice timing measurement is essential for TOF-PET,a Monte Carlo model was built to observe various factors that effect timing resolution,including scintillator parameters,transit time speads,single photon response,dark counter and electronic noise.A method based on the concept of best threshold crossover time was proposed to analysis the effect of circuit bandwidth and noise on timing resolution.The current mode input stage was adopted to readout SiPM signal,and circuit parameters were optimized so that timing resolution of the detector will not be degraded by the readout circuit.In multi-channel timing measurement systems,threshold non-uniformity is a common phenomenon,which might cause timing inaccuracy and other problems,and non-uniformity is especially considerable for the chosen current mode circuit structure.Threshold fine adjusting circuit was designed,and an automatic online threshold calibration method was proposed.This calibration method exploits the dark count property of SiPM,and was verified by experiments.A 64-channel application specific integrated circuit(ASIC)named EXYT was developed.It integrates individual fast readout for timing and resistive networks for energy and position measurements.Gated summation circuits were implemented to suppress the dark count noise and to reduce the dead time.The chip was fabricated with 0.18 ?m CMOS technology.All the functions of EXYT have been tested and verified,and the power consumption is only 3m W per channel.Detector module based on EXYT and SiPM array was also developed and tested.Sub-pixel resolution can be achieved when coupled to a 16×16 array of 2×2×14 mm3 LYSO crystals,with an average energy resolution of 15%.Coincidence resolving time(CRT)was measured to be less than 300 ps(FWHM)for 2×2×14mm3 LYSO crystal(s),which fulfilled TOF-PET detector requirements.Furthermore,time-based readout scheme for SiPM array was studied.Two different readout ASICs,based on charge-to-time method and time-over-threshold method,have been developed and verified.These readout solutions are suitable for high counting rate and/or accurate energy measurement applications,and can be alternatives to EXYT solution.