An analogue front-end ASIC prototype designed for PMT signal readout

Abstract

The Large High Altitude Air Shower Observatory (LHAASO) is designed for high energy gamma ray and cosmic ray detection. A Water Cherenkov Detector Array which is sensitive to gamma ray showers above a few hundred GeV is proposed to survey gamma ray sources. The WCDA consists of 3600 PhotoMultiplier Tubes (PMT) which collect the Cherenkov light produced by the shower particles in water. Both high precision time and charge measurement are required over a large dynamic range from 1 photo electron (P.E.) to 4000 P.E. Prototype of an analogue front-end Application Specific Integrated Circuit (ASIC) fabricated in Chartered 0.35 μm CMOS technology is designed to read out PMT signal in the WCDA. This ASIC employs leading edge discrimination and RC 4 shaping structure; combined with the following Time-to-Digital Converter (TDC) and Analog-to-Digital Converter (ADC), both the arrival time and charge of the PMT signal can be measured. Initial test results indicate that time resolution is better than 350 ps and charge resolution is better than 10% at 1 P.E. and better than 1% with large input signals (300 P.E. to 4000 P.E.). Besides, this ASIC has a small channel-to-channel crosstalk and low ambient temperature dependency.

A 12-bit 30 MS/s SAR ADC in 180 nm CMOS for PMT signal readout

“…In this paper, we focus on the readout scheme which utilizes shaping circuits and ADCs for the charge measurement, and the design of a Successive Approximation Register (SAR) ADC is presented. This ADC works with an analog front-end ASIC [11] which we previously designed for PMT readout. As shown in figure 2, signals from both the anode and the dynode of one PMT are sent to the analog front-end ASIC and are shaped by the RC 4 shaping circuits, with a configurable peaking time from 60 ns to 150 ns.…”