High-speed charge-to-time converter ASIC for the Super-Kamiokande detector

TL;DR

This paper presents a high-speed, multi-channel ASIC designed for efficient charge measurement of photomultiplier tube signals in large detectors, offering high dynamic range, linearity, and timing resolution.

Contribution

The development of a novel charge-to-time converter ASIC with high rate capability, wide dynamic range, and integrated features tailored for large-scale neutrino detectors.

Findings

Achieved >1MHz signal processing rate.

Demonstrated 0.2 pC charge resolution and 1% linearity.

Validated performance through comprehensive testing.

Abstract

A new application-specific integrated circuit (ASIC), the high-speed charge-to-time converter (QTC) IWATSU CLC101, provides three channels, each consisting of preamplifier, discriminator, low-pass filter, and charge integration circuitry, optimized for the waveform of a photomultiplier tube (PMT). This ASIC detects PMT signals using individual built-in discriminators and drives output timing signals whose width represents the integrated charge of the PMT signal. Combined with external input circuits composed of passive elements, the QTC provides full analog signal processing for the detector's PMTs, ready for further processing by time-to-digital converters (TDCs). High-rate (>1MHz) signal processing is achieved by short-charge-conversion-time and baseline-restoration circuits. Wide-range charge measurements are enabled by offering three gain ranges while maintaining a short cycle time. QTC chip test results show good analog performance, with efficient detection for a single photoelectron signal, four orders of magnitude dynamic range (0:3mV ~ 3V; 0:2 ~ 2500 pC), 1% charge linearity, 0.2 pC charge resolution, and 0.1 ns timing resolution. Test results on ambient temperature dependence, channel isolation, and rate dependence also meet specifications.