Basic description and performance test of the analog signal processing electronics for MADPET-II

MADPET-II is a small animal PET scanner currently under development, that provides individual channel readout for each one of its 1152 LSO-APD electronic channels. In order for such a large number of channels to be processed individually, the analog signal processing electronics are fully integrated into single monolithic chips. Each chip contains a differential receiver, a shaping amplifier, a peak hold detector and a non-delay line constant fraction discriminator. In the CFD the delay line has been replaced by a high pass CR circuit, which can result in comparable timing resolution. The performance of the chip has been tested by studying the output signals of the shaper, the peak detector and the CFD. The bias currents have been adjusted 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 = 0.9961). The walk performance of the CFD can be adjusted by changing the R component of the CR high pass filter, and it can be minimized to approximately 2 nsec over a 5:1 amplitude input dynamic range. An improved version of the chip will have a different value of the C component of the CR high pass circuit. Its timing performance is expected to improve and be less sensitive to variations in changes to the R component of the high pass filter. From simulations, the walk is expected to be approximately 200ps over a 5:1 amplitude dynamic range.