HRFlexToT: A High Dynamic Range ASIC for Time-of-Flight Positron Emission Tomography

Time-of-Flight Positron Emission Tomography (TOF-PET) scanners demand fast and efficient photo-sensors and scintillators coupled to fast readout electronics. This paper presents the HRFlexToT, a 16-channel ASIC for SiPM anode readout manufactured using XFAB 0.18 μm CMOS technology. The main features of the HRFlexToT are a linear Time-over-Threshold (ToT) with an extended dynamic range (10 bits) for energy measurement, low power consumption (≈ 3.5 mW/ch), and an excellent timing response. Experimental measurements show an energy linearity error of ≈ 3% and an energy resolution of about 12% at 511 keV. Single-Photon Time Resolution (SPTR) measurements performed using an FBK SiPM NUV-HD (4 × 4 mm2 pixel, 40 μm cell) and a Hamamatsu SiPM S13360-3050CS are around 142 ps and 167 ps full width at half maximum (FWHM), respectively. Coincidence Time Resolution (CTR) measurements with small cross-section pixelated crystals (LSO:Ce,Ca 0.4%, 2 × 2 × 5 mm3) coupled to the same Hamamatsu S13360-3050CS and FBK NUV-HD sensors yield a CTR of 117 ps and 119 ps, respectively. Measurements performed with a large cross-section monolithic crystal (LFS crystal measuring 25 × 25 × 20 mm3) and a Hamamatsu SiPM array S13361-6050NE-04 show a CTR of 324 ps FWHM after time-walk and time-skew correction.