Testing of Front-End Readout Prototype ASICs Designed for WCDA in LHAASO

TL;DR

This paper presents the design and testing of prototype ASICs for the WCDA readout system in LHAASO, achieving high precision timing and charge measurements over a large dynamic range to enhance detector performance.

Contribution

The paper introduces two novel ASIC prototypes for WCDA readout, demonstrating improved timing and charge resolution suitable for high-energy gamma ray detection.

Findings

Time resolution better than 250 ps RMS

Charge resolution better than 10% at 1 P.E.

Charge resolution better than 1% at 4000 P.E.

Abstract

The water Cherenkov detector array (WCDA) is one of the key detectors in the large high altitude air shower observatory (LHAASO), which is proposed for very high gamma ray source survey. In WCDA, there are more than 3000 photomultiplier tubes (PMTs) scattered under water in an area of 80000 m2. As for the WCDA readout electronics, both high precision time and charge measurement is required over a large dynamic range from 1 photon electron (P.E.) to 4000 P.E. To reduce the electronics complexity and improve the system reliability, a readout scheme based on application specific integrated circuits (ASICs) is proposed. Two prototype ASICs were designed and tested. The first ASIC integrates amplification and shaping circuits for charge measurement and discrimination circuits used for time measurement. The shaped signal is further fed to the second ADC ASIC, while the output signal from the discriminator is digitized by the FPGA-based time-to-digital converter (TDC). Test results indicate that time resolution is better than 250 ps RMS, and the charge resolution is better than 10% at 1 P.E., and 1% at 4000 P.E. which meets the requirements of the LHAASO WCDA.