Title: Development of a 32-channel ASIC for an X-ray APD Detector onboard the ISS,
Abstract: We report on the design and performance of a mixed-signal application
specific integrated circuit (ASIC) dedicated to avalanche photodiodes (APDs) in
order to detect hard X-ray emissions in a wide energy band onboard the
International Space Station. To realize wide-band detection from 20 keV to 1
MeV, we use Ce:GAGG scintillators, each coupled to an APD, with low-noise
front-end electronics capable of achieving a minimum energy detection threshold
of 20 keV. The developed ASIC has the ability to read out 32-channel APD
signals using 0.35 $\mu$m CMOS technology, and an analog amplifier at the input
stage is designed to suppress the capacitive noise primarily arising from the
large detector capacitance of the APDs. The ASIC achieves a performance of 2099
e$^{-}$ + 1.5 e$^{-}$/pF at root mean square (RMS) with a wide 300 fC dynamic
range. Coupling a reverse-type APD with a Ce:GAGG scintillator, we obtain an
energy resolution of 6.7% (FWHM) at 662 keV and a minimum detectable energy of
20 keV at room temperature (20 $^{\circ}$C). Furthermore, we examine the
radiation tolerance for space applications by using a 90 MeV proton beam,
confirming that the ASIC is free of single-event effects and can operate
properly without serious degradation in analog and digital processing.