Front-end electronics for the RatCAP mobile animal PET scanner: timing discriminator and 32 line address priority serial encoder

We report on the development of the integrated front-end electronic for the RatCAP (Rat Conscious Animal PET). The RatCAP is a head-mounted, APD-based portable positron emission tomography scanner intended to perform brain imaging and behavioral studies of the awake rat. This paper focuses on the development and characterization of the zero-crossing discriminator (ZCD) and the 32 line address serial encoder for the miniature scanner. The ZCD, used as a time pick-off circuit for each APD detector, has a power consumption of only 300 μW. The 32 line address serial encoder is used to multiplex the timing edge of every channel together with its address into a single output. The ASIC, realized in a CMOS 0.18 μm process, has a maximum power dissipation of 125 mW. The electronic timing jitter, the time walk and the coincidence timing resolution of the ZCD measured at the encoder output are presented.