Fast circuit topology for spatial signal distribution analysis

We present a novel active and analog readout and preprocessing topology for position sensitive photodetectors (PSPD) that allows to readout a large variety of PSPD devices with different pixel numbers. Additionally, the topology was designed to allow for a significant reduction of analog-to-digital conversion channels. The circuit topology replaces the common passive charge divider and consists of N input stages, N × M weighting stages and M analog adder stages, where N is the number of the input channels, i.e. the number of photodetector pixels and M is the number of outputs. The circuit performs the multiplication of a matrix (the weights) with a vector (signals). For this, the input stage makes M copies of each of the N input signals, the weighting stage multiplies these signal copies with N × M different weights and the output stage adds all weighted copies with the same copy index. For high flexibility, the weights are programmable and the topology allows to interconnect several identical circuits for larger N. As application for the circuit, we present a Neural Network based positioning scheme for γ-ray imaging detectors with thick, monolithic scintillation crystals. We used Monte Carlo simulation for training and evaluation of the method and found that the spatial resolution of the γ-ray imaging detectors was significantly enhanced. The strong border artifacts of the center of gravity positioning scheme in monolithic scintillation crystals could be corrected to a large extent.