Front-end ASIC for Spectroscopic Readout of Virtual Frisch-Grid CZT Bar Sensors

Compact multi-channel radiation detectors rely on low noise front-end application specific integrated circuits (ASICs) to achieve high spectral resolution. Here, a new ASIC developed to readout virtual Frisch-grid cadmium zinc telluride (VFG CZT) detectors for gamma ray spectroscopy is presented. Corresponding to each ionizing event in the detector, the ASIC measures the amplitude and timing at the anode, the cathode and four pad sense electrodes associated with each sensor in a detector array. The ASIC is comprised of 52 channels of which there are 4 cathode channels and 48 channels which can be configured as either anode channels with a baseline of 250 mV or pad sense channels to process induced signals with a baseline of 1.2 V. With a static power dissipation of 3 mW, each channel performs low-noise charge amplification, high-order shaping, peak and timing detection along with analog storage and multiplexing. The overall channel linearity was better than $\pm$ 1 % with timing resolution down to 700 ps for charges greater than 8 fC in the 3 MeV range. With a 4 x 4 array of 6 mm x 6 mm x 20 mm virtual Frisch-grid bar sensors connected and biased, an electronic resolution of $\approx$ 270 rms $e^{-}$ for charges up to 100 fC in the 3.2 MeV range was measured. Spectral measurements obtained with the 3D correction technique demonstrated resolutions of 1.8 % FWHM at 238 keV and 0.9 % FWHM at 662 keV.