An analog signal processing ASIC for a small animal LSO–APD PET tomograph

MADPET-II is a small animal PET scanner currently under development that provides individual readout for each one of its 1152 LSO–APD electronic channels. In order to process such a large number of channels individually, the analog signal processing electronics are fully integrated into monolithic chips. Each chip contains four independent differential receivers, shaping amplifiers, peak hold detectors and non-delay line constant-fraction discriminators (CFDs). The CFDs use a high-pass CR circuit rather than the conventional delay line to generate a bipolar pulse. The performance of the chip has been tested for walk, jitter and pulse height linearity by studying the peak detector and the CFD signals, and has been optimized by adjusting the corresponding bias currents so as to maximize the signal-to-noise ratio and to minimize the walk of the CFD output (trigger). The response of the peak detector to different input signal amplitudes is linear (R2=0.99945±0.00002)(R2=0.99945±0.00002). The walk performance of the CFD can be adjusted by changing the offset of the CR high-pass filter output signal, and can be minimized to approximately 2 ns over a 5:1 input amplitude dynamic range.