Initial Measurements with the PETsys TOFPET2 ASIC Evaluation Kit and a Characterization of the ASIC TDC

TL;DR

This study evaluates the PETsys TOFPET2 ASIC with SiPMs and LYSO crystals, analyzing timing, energy resolution, and temperature effects, providing initial performance benchmarks and insights into satellite peak origins.

Contribution

First characterization of the PETsys TOFPET2 ASIC with detailed measurements of timing, energy resolution, and temperature effects, including analysis of satellite peaks and trigger circuit delays.

Findings

Achieved 10% energy resolution at 6 V overvoltage

Obtained 210 ps FWHM coincidence resolving time

Identified correlation between satellite peaks and trigger delay

Abstract

For a first characterization, we used the two KETEK-PM3325-WB SiPMs each equipped with a 3x3x5 mm${}^3$ LYSO scintillation crystal provided with the PETsys TOFPET2 ASIC Evaluation Kit. We changed the lower of two discriminator thresholds (D_T1) in the timing branch from vth_t1 = 5 - 30. The overvoltage was varied in a range of 1.25 V - 7.25 V. The ambient temperature was kept at 16{\deg}C. For all measurements, we performed an energy calibration including a correction for saturation. We evaluated the energy resolution, the coincidence resolving time (CRT) and the coincidence rate. At an overvoltage of 6 V, we obtained an energy resolution of about 10% FWHM, a CRT of approximately 210 ps FWHM and 400 ps FWTM, the coincidence rate showed only small variations of about 5%. To investigate the influence of the ambient temperature, it was varied between 12{\deg}C - 20{\deg}C. At 12{\deg}C and an overvoltage of 6.5 V, a CRT of approx. 195 ps FWHM and an energy resolution of about 9.5% FWHM could be measured. Observed satellite peaks in the time difference spectra were investigated in more detail. We could show that the location of the satellite peaks is correlated with a programmable delay element in the trigger circuit.