A High Dynamic Range ASIC for Time of Flight PET with pixelated and monolithic crystals

The HRFlexToT is a 16-channel ASIC for SiPM anode readout with common cathode connection. It is designed for Positron Emission Tomography (PET) applications and it features high dynamic range (>8 bits), low input impedance, high speed and low power (~3,5 mW/ch). The ASIC has been manufactured using XFAB 0.18 μm CMOS technology. The main characteristics of the HRFlexToT are a new energy measurement readout providing a linear Time over Threshold (ToT) with an extended dynamic range, lower power consumption and better timing response. Initial measurements show an energy linearity error below 3%. Single Photon Time Resolution (SPTR) measurements performed using a Hamamatsu MPPC S13360-3050CS (3×3 mm
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, 50 μm cell) shows 30% improvement with respect to the previous version of the ASIC, setting this specification in the order of 141 ps FWHM and reducing 3 times power consumption. Coincidence Time Resolution (CTR) measurements with small cross-section pixelated crystals (LFS crystal, 3×3×20 mm
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) coupled to a single SiPM (S13360-3050CS, 3×3 mm
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and 50 μm pixel pitch) provides a CTR of 180 ps FWHM. Monolithic measurements performed with a larger cross-section crystal (LFS crystal of 25×25×20 mm
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) and an SiPM array (S13361-6050NE-04, 6×6 mm
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and 50 μm pixel pitch) shows a CTR of 280 ps FWHM after time-walk and skew calibration. Monolithic measurements were taken using a 2×2×5 mm
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LSO:Ce Ca 0.2% coupled to a S13360-3050CS as a reference detector (90 ps FWHM jitter).