Design of a fast shaping amplifier for PET/CT APD detectors with depth-of-interaction

An integrated, 0.35 /spl mu/m CMOS fast shaping amplifier has been designed for coincidence detection and zero-cross time pulse shape discrimination (PSD) in PET, and for high rate event counting in CT with APD-based detectors. Analytical simulations of CR-RC/sup n/ filters of various order and shaping time constant were carried out to optimize the timing performance, keeping in mind the stringent channel density requirements of the detector front-end electronics. The filter was implemented with the biquadratic bandpass architecture using a folded cascode transconductance amplifier. The electronic timing resolution of the coincidence circuit was 92 ps in the ideal case without an APD (Cin=0pF), and 243 ps with an APD (Cin=30 pF). By comparison, the same system with the CMOS shaper replaced by an Ortec 579 Fast Filter Amplifier set to a shaping time of 10 ns yielded an electronic time resolution of 79 ps in the ideal case without capacitance, and 236 ps with the APD. The 511 keV coincidence time resolution for an LSO/APD detector was measured to be 1.49 ns.