Performance of a 2-keV digitizer ASIC for 3-D position-sensitive pixellated semiconductor detectors

V AD_UM ASIC is a 124-channel pre-amplifier waveform digitizer for 3-D position-sensitive pixllated semiconductor detectors, with a measured 2-keV FWHM electronic noise at room temperature. Excellent energy resolutions of 0.41% FWHM at 662 keY and 0.27% FWHM at 2.6 MeV have been achieved on a 6 cm³ CZT detector (detector # 4E-l) for single-pixel events with a 3-MeV dynamic range. Depth separation for any two interactions is critical for Compton gamma-ray imaging. With this VAD_UM ASIC, the uncertainty of depth separation is found to be as small as 0.5 mm FWHM at 300 keY. A coincidence experiment using a plastic scintillator was carried out to measure the timing performance of the system. The result showed ~15 ns FWHM timing resolution for many anode pixels.