Analysis of position error generated in readout resistive network for gamma-ray detection system

Detectors such as photomultiplier tubes (PMT) and Si photomultipliers (SiPM) in array are used in the gamma-ray detection system. They convert the light to electrical signal in the form of a current pulse by photoelectric effect. Because size and power consumption of the detection system is determined by the number of output channels in the detector, a resistive network such as a discretized positioning circuit (DPC) has been used for reducing the number of output channels. The current pulse generated in the detector is distributed to four output ports according to a ratio by resistance of the DPC. Then, the distributed current pulses convert voltage pulses by a charge sensitive amplifier (CSA). The detected positions are estimated by the peak value of the four CSA outputs. However, the position errors occur due to the impedance difference between output of the DPC and input of the CSA. In this paper, we calculated input impedance of the CSA according to variation of CSA's feedback component. Also, we analyzed the cause of position error generated by the impedance difference.