A fast preamplifier concept for SiPM-based time-of-flight PET detectors

Silicon photomultipliers (SiPMs) offer high gain and fast response to light, making them interesting for fast timing applications such as time-of-flight (TOF) PET. To fully exploit the potential of these photosensors, dedicated preamplifiers that do not deteriorate the rise time and signal-to-noise ratio are crucial. Challenges include the high sensor capacitance, typically >300pF for a 3mm×3mm SiPM sensor, as well as oscillation issues. Here we present a preamplifier concept based on low noise, high speed transistors, designed for optimum timing performance. The input stage consists of a transimpedance common-base amplifier with a very low input impedance even at high frequencies, which assures a good linearity and avoids that the high detector capacitance affects the amplifier bandwidth. The amplifier has a fast timing output as well as a ‘slow’ energy output optimized for determining the total charge content of the pulse. The rise time of the amplifier is about 300ps. The measured coincidence resolving time (CRT) for 511keV photon pairs using the amplifiers in combination with 3mm×3mm SiPMs (Hamamatsu MPPC-S10362-33-050C) coupled to 3mm×3mm×5mm LaBr3:Ce and LYSO:Ce crystals equals 95ps FWHM and 138ps FWHM, respectively.