A High-Speed Low-Noise 16-Channel CSA With Automatic Leakage Compensation In 0.35-$\mu$m CMOS Process for APD-Based PET Detectors

Design, implementation, analysis and measured performance results of a new high-speed low-noise 16-channel charge-sensitive preamplifier (CSA) prototype with automatic detector leakage compensation are presented. The prototype has been fabricated in TSMC 0.35-mum CMOS process and is designed for use with avalanche photodiode (APD) based PET detectors. The CSA is used to read out charge signals from a 4times4 APD array having 3 pF of capacitance and 75 nA of leakage current per pixel. A single channel CSA has 16 gain settings measured to range from 31.7 mV/fC to 4.5 mV/fC. The gain settings for all channels are set by a 64-bit on-chip shift register. The signal rise time at the CSA output was measured to be as fast as 2.9 ns (5%-55% rise time) and 4.8 ns (20%-80% rise time). A feedback MOS transistor biased in the triode region is used to reset the CSA output and a very slow Gm-feedback loop performs automatic leakage compensation up to 10 muA of leakage current per channel. Minimum input referred rms noise of 350 e- was measured with a pure capacitive input load and 1200 e- with an actual APD load biased at -1.7 kV connected to the CSA input, both at 0.1-mus peaking time. The prototype chip draws less than 50 mA of total current from a +3.3 V supply.