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

An integrated, 0.35mum 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-RCn 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 92ps in the ideal case without an APD (Cin = 0pF), and 243ps with an APD (Cin = 30pF). By comparison, the same system with the CMOS shaper replaced by an Ortec 579 Fast Filter Amplifier set to a shaping time of 10ns yielded an electronic time resolution of 79ps in the ideal case without capacitance, and 236ps with the APD. The 511keV coincidence time resolution for an LSO/APD detector was measured to be 1.49ns.