GAMMA: an 8-channel High Dynamic Range ASIC for SiPM-Based Readout of Large Scintillators

Abstract

LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> crystals are well known to provide the brightest light pulses among commercially available scintillators. Recent developments in SiPMs brought to the market low-darkcount, high-PDE photodetectors that can offer high dynamic range readout of LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> . While state-of-the-art front-end electronics is suitable for standard dynamic range applications, e.g. for PET, experiments needing large DR require novel solutions. Our project aims at developing a wide DR (100 keV - 20 MeV) gamma spectrometer and imager with state-of-the-art energy resolution. In order to design a specific front-end for the application, the signal range impinging on every different SiPM was simulated and measured. Results of preliminary measurements showed that higher the energy impinging the crystal higher is the signal spread among the channels. The charge spread was then estimated to be 3 pC - 3nC, to be acquired without any gain change during the acquisition. The input stage was designed to read the current and scale it down to be processed by the following filter. The timevariant filter was designed to act as a self-triggered gated integrator. In order to exploit all the estimated charge range it was implemented a signal dependent Active Gain Control (AGC): the gain is proportionally reduced in order to increase the saturation charge to 2.5 nC. Measurements were performed in order to demonstrate the working principle of the AGC, verify the resulting dynamic range and the crosstalk between channels. 80 dB DR was measured and AGC proved its functionality. Experimental measurements were also performed in order to verify spectroscopy resolution: 3.8% at 622 keV was measured at room temperature.