Low electronic noise digital ASIC array system and its non-linearity

Due to the large number of pixels on pixelated CdZnTe detectors, application-specific integrated circuits (ASICs) have been adopted for effective readout. An energy resolution of 0.48% FWHM at 662 keV has been achieved on a large volume (20×20×15mm³) CdZnTe detector with an analog ASIC designed by Brookhaven National Lab(BNL). Gamma Medica-Ideas (GM-I) has developed a digital ASIC which can provide digitized pre-amplifier waveforms for every pixel. The current digital ASIC system consists of a 2 by 2 array of ASIC modules with each module having an equivalent electronic noise of 2 keV. Thanks to the low electronic noise, the spectroscopic performance is similar to what has been achieved by the BNL ASIC. The non-linearity of this digital array system has been studied using various radiation sources with different energies. Since there are four ASICs in this array system, gamma-ray interactions may occur in more than one detector, which are called inter-module events in this study. The energy resolution of these events is worse than expected when compared to an analog array system. This paper investigates the origin of the energy resolution discrepancy observed in inter-module events. This work will also help find energy resolution degradation factors for single detector, multiple pixel events.