Prototype of a front-end readout ASIC designed for the Water Cherenkov Detector Array in LHAASO

TL;DR

This paper presents a prototype front-end readout ASIC for the Water Cherenkov Detector Array in LHAASO, capable of high-precision charge and time measurements across a wide dynamic range, simplifying signal processing.

Contribution

The design and fabrication of a novel ASIC integrating time discrimination and charge-to-time conversion in 0.35 μm CMOS technology for high-energy physics applications.

Findings

Achieved time resolution better than 0.5 ns across full dynamic range

Charge resolution better than 1% for large signals

Maintained charge resolution better than 15% at single photoelectron level

Abstract

The Large High Altitude Air Shower Observatory is in the R&D phase, in which the Water Cherenkov Detector Array is an important part. The signals of Photo-Multiplier Tubes would vary from single photo electron to 4000 photo electrons, and both high precision charge and time measurement is required. To simplify the signal processing chain, the charge-to-time conversion method is employed. A prototype of the front-end readout ASIC is designed and fabricated in Chartered 0.35 {\mu}m CMOS technology, which integrates time disctrimination and converts the input charge information to pulse widths. With Time-to-Digital Converters, both time and charge can be digitized at the same time. We have conducted initial tests on this chip, and the results indicate that a time resolution better than 0.5 ns is achieved over the full dynamic range (1~ 4000 photo electrons, corresponding to 0.75 ~ 3000 pC with the threshold of 0.188 pC); the charge resolution is better than 1% with large input amplitudes (500 ~ 4000 photo electrons), and remains better than 15% with a 1 photo electron input amplitude, which is beyond the application requirement.