A Programmable Low-Power, Low-Noise Front-End Channel in 0.35-mu m CMOS for CdZnTe detectors

A programmable low-power, low-noise readout circuit for Cadmium Zinc Telluride (CdZnTe or CZT) detectors is presented. CdZnTe detectors encompass a wide range of applications such as medical imaging and astrophysics. The front-end comprises a charge-sensitive amplifier (CSA), a programmable reset network with dark current compensation capability, a fifth-order semi-Gaussian filter with pole-zero cancellation, a comparator, and serial interface to communicate with external microcontroller. Utilizing the programmablity of the reset-network, the CSA can provide 256 different discharge time-constants, ranging from 60n to 600 mu seconds, making the readout suitable for a wide range of event-rates. The application-specific integrated circuit (ASIC) is designed and simulated in a 0.35- mu m 3.3V C35 CMOS process of Austria Micro-Systems. The ASIC has a power consumption of less than 2 mW per channel and the CSA only consumes 260 mu W stable with a feedback capacitance of 60 fF which contributes to a conversion gain of 135 mV/fC. Equivalent Noise Charge (ENC) is 98 erms @ 0 pF detector capacitance.