Development of a 64-Channel Readout ASIC for an 8 x 8 SSPM Array for PET and TOF-PET Applications

In this paper, we developed a 64-channel application specific integrated circuit (ASIC) named EXYT for 8 x 8 SSPM arrays for positron emission tomography (PET) and time-of-flight (TOF)-PET applications. It integrates individual fast readout for timing and resistive networks for energy and position measurements, which reduces the outputs down to 4 differential signals: Timing, Energy and X/Y positions. Gated summation circuits were implemented to suppress the dark count noise and to reduce the dead time. An automatic threshold calibration method was also introduced in this paper and the threshold difference among all the channels could be effectively reduced to < 1 p.e. by adjusting a local 5-bit DAC for each channel. The chip has been fabricated with 0.18 mu m CMOS technology. Evaluation system with SSPM array and LYSO crystals has been developed. All the functions of EXYT have been tested and verified. The power consumption is 3 mW per channel. Energy resolution of 12% and coincidence resolving time (CRT) of 363 ps (FWHM-full width at half maximum) have been achieved for 2 x 2 x 14 mm(3) LYSO crystal(s). Sub-pixel resolution can be achieved when coupled to a 12 x 12 array of 2.7 x 2.7 x 14 mm(3) LYSO crystals.