Readout ASIC for 3D Position-Sensitive Detectors

We describe an application specific integrated circuit (ASIC) for 3D position-sensitive detectors. It was optimized for pixelated cadmium-zinc-telluride (CZT) sensors, and it measures, corresponding to an ionizing event, the energy and timing of signals from 121 anodes and one cathode. Each channel provides low-noise charge amplification, high-order shaping, along with peak- and timing-detection. The cathode´s timing can be measured in three different ways: the first is based on multiple thresholds on the charge amplifier´s voltage output; the second uses the threshold crossing of a fast-shaped signal; and the third measures the peak amplitude and timing from a bipolar shaper. With its power of 2 mW per channel the ASIC measures, on a CZT sensor connected and biased, charges up to 100 fC with an electronic resolution better than 200 e^- rms. Our preliminary spectral measurements applying a simple cathode/anode ratio correction demonstrated a single-pixel resolution of 4.8 keV (0.72 %) at 662 keV, with the electronics and leakage current contributing in total with 2.1 keV.