STIC — A current mode constant fraction discriminator for Positron Emission Tomography using SiPM (MPPC)

Silicon photomultipliers (SiPMs) are a novel type of solid state photon detectors with similar internal gain factors as Photomultiplier Tubes (PMTs). Due to their low operation bias voltage, magnetic field immunity and small size, these new silicon photon detectors can be used for a wide range of applications, in particular Positron Emission Tomography (PET). Using combined crystal/SiPM systems for detecting the 511 kev photons in PET applications leads to a large current output due to the typically large gain and the large pixel number of SiPMS. Hence, a novel current-mode monolithic readout scheme can be used for signal extraction. As an important time pick-up unit, constant fraction discriminators are generally used in PET for coincidence measurements. Here, we report on a current mode constant fraction discriminator using a current mode non-delay-line method to generate the bipolar shape for the zero-crossing timing. A first test chip (STIC), using this scheme has been designed and submitted in AMS 0.35 ¿m CMOS technology.