A low-noise, wide-band CMOS charge-sensitive preamplifier for use with a cadmium zinc telluride strip detector in a high-resolution small animal x-ray CT system

A low-noise, wide-band CMOS charge-sensitive preamplifier has been designed for use with a Cadmium Zinc Telluride (CZT) strip detector in the Oak Ridge NationalLaboratory's (ORNL) MicroCAT small animal x-ray CT imaging system. The Characteristics of the CZT strip detector have been studied to optimize the design of the preamplifier, and are presented herein. The design of the charge-sensitive preamplifier(CSP) is discussed in detail, and test results are presented and discussed. The CSP was found to have a 10 - 90 % rise time of 23 ns, a charge gain of √ Hz x 10¹² V/C, a dynamic range of + 0.9 V and - 2 V, and an equivalent input noise of 13 .nV√Hz 1 kHz and 2.2 nV 1 MHz. The CSP coupled to an Ortec 571 shaping amplifier has an Equivalent Noise Charge (ENC) minimum of 400 rms electrons for unipolar shaping at peaking time of 14 µs with a 4 pF detector capacitance. The system, with the same configuration, hasan ENC minimum of 550 rms electrons for bipolar shaping at the zero crossover of 15 µs.The prototype preamplifier has been fabricated in the AMI 1.2 µm process through the MOSIS microelectronics prototyping program.