Pulse train multiplexing method for pixellated gamma detectors

Architecture of high-density Front-End electronics is very important for high-resolution pixcellated gamma detector system such as PET or gamma camera. We propose a novel front-end pulse processing scheme with Pulse Width Modulation (PWM) and Pulse Train Method. Each channel of the proposed front-End consists of a preamplifier, a shaping amplifier, a comparator and digital/analog circuit which generates a pulse train. Preamplifier/ Shaper/ Discriminator module generates a first trigger pulse using Time over Threshold (ToT) which contains energy information. Then the additional pulse which expresses the group or ASIC chip address is generated after the trigger pulse to form the pulse train. This additional pulse is unique in each ASIC chip to indicate the chip address where the signal comes from. Output digital pulse train of each ASIC can be connected simply by Wired-OR logic and the number of transmission line in a whole system can be greatly reduced. The pulse width encoding also simplifies the following digital processing parts. This pulse train multiplexing method is useful for pixellated gamma detectors.