STiC2 - characterization results of a SiPM readout ASIC for time-of-flight applications

STiC is a mixed-mode readout ASIC for silicon-photomultipliers (SiPM) developed in the framework of the EndoToFPET-US project. The chip has been designed in the UMC 0.18 μm technology and aims to provide an optimal timing resolution to Time-of-Flight measurements in medical imaging and particle physics applications. The differential design of the analog input stage rejects noise from the large integrated digital part as well as external sources. The chip allows either a differential or a single-ended readout of the sensors. The time and charge information of the input signal is converted into two time stamps which are digitized by an integrated TDC module with a time binning of 50 ps. A special linearized Time-over-Threshold method has been implemented to provide a linear response to the signal charge in a wide range. The digitized event information is stored in a 64-word FIFO memory and transmitted every 6.4 μs to an external DAQ system using a 160 MBit=s LVDS serial link with 8/10-bit encoding. Characterization measurements show a trigger jitter of σ <; 30 ps for input signals larger than 3 pC injected over a 33 pF capacitor. A measurement using 3.1 × 3.1 × 15mm
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LYSO crystals and Hamamatsu MPPC (S10362-33-50C) sensors to detect coincidence photons from positron annihilations shows an energy resolution of ~ 12% for the 511 keV peak and a coincidence time resolution of 220 ps FWHM. We present details of the ASIC design as well as characterization measurements.