Development of a low noise readout ASIC for CZT detectors for gamma-ray spectroscopy applications

A multi-channel readout ASIC for pixelated CZT detectors has been developed for gamma-ray spectroscopy applications. Each channel consists of a low noise dual-stage charge sensitive amplifier (CSA), a CR-(RC)(4) semi-Gaussian shaper and a class-AB output buffer. The equivalent noise charge (ENC) of input PMOS transistor is optimized for 5 pF input capacitance and 1 mu s peaking time using g(m)/I-D design methodology. The gain can be adjusted from 100 mV/fC to 400 mV/fC and the peaking time can be adjusted from 1 mu s to 4 mu s. A 16-channel chip has been designed and fabricated in 0.35 mu m m 2P4M CMOS technology. The test results show that the chip works well and fully satisfies the design specifications. The ENC was measured to be 72 e + 26 e/pF at 1 mu s peaking time and 86 e + 20 e/pF at 4 mu s peaking time. The non-uniformity of the channel gain and ENC was less than +/- 12% and +/- 11% respectively for 16 channels in one chip. The chip was also tested with a pixelated CZT detector at room temperature. The measured energy resolution at 59.5 keV photopeak of Am-241 and (122)keV photopeak of Co-57 were 4.5% FWHM and 2.8% FWHM for the central area pixels, respectively.