Evaluation of a front-end ASIC prototype for the readout of PMTs in Water Cherenkov Detector Array

Water Cherenkov Detector Array (WCDA) in the Large High Altitude Air Shower Observatory has been proposed to survey gamma ray sources. The WCDA consists of 3600 Photo-Multipliers (PMTs) under water and the signals of PMTs would vary from 1 photo electron (P.E.) to 4000 P.E. In this paper, we propose an analogue front-end Application Specific Integrated Circuit (ASIC) prototype which is fabricated in Chartered CMOS 0.35µm technology to read out the PMT signal in the WCDA. The ASIC integrates dual-threshold time discrimination circuits and RC4 shaping circuits; combined with following time-to-digital converter (TDC) and analogue-to-digital converter (ADC), both time and charge measurement can be achieved. We have conducted initial tests on this chip, and the results indicate that time resolution is better than 350 ps and charge resolution is better than 10% @1 P.E. and 1% with large input signals. Both time and charge resolution is beyond the application requirement.