Analysis of Digital Waveform Methods with DRS4 Evaluation Board

Key words: 
• LaBr3 /
• DSR4 /
• time resolution

Abstract: Various digital methods were examined for determining the relative arrival times of pulses from 20 mm x 5 mm LaBr3 scintillators. In this study, pulses from the photomultiplier tubes (PMTs) were digitized by DRS4 evaluation board, a switched capacitor array (SCA) produced by the Paul Scherrer Institute (PSI). The high bandwidth, low power consumption and short readout time make DRS4 attractive for many experiments, replacing traditional ADCs and TDCs. The sampling signals were post processed with multiple techniques. These techniques include: (1) constant-raction discrimination (CFD), (2) pulse-shape fitting, (3) mean PMT pulse model and (4) median filtered zero crossing method.The implemented CFD in the digital regimes did not improve the resolution of using analog equipmentwith average time resolution. The pulse-shape fitting yielded as good resolution as digital CFD, however,is much more time consuming. The median filtered method were easy to implement, and had a resolution on the order of sampling time. Average timing resolutions of 195.4 ps were obtained with mean PMT pulse model, which is better than the analog constant-fraction-zero-crossing with average resolution of 254.7 ps.