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

Abstract

A new application-specific integrated circuit (ASIC), the high-speed chargeto-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 (>1 MHz) signal processing is achieved by short-charge-conversiontime 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, 4 orders of magnitude dynamic range (0.3 mV ∼ 3 V; 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.

Indication of Electron Neutrino Appearance from an Accelerator-Produced Off-Axis Muon Neutrino Beam

“…Each board is equipped with 8 QTCs, each of which has three PMT input channels. More information on the QBEEs, especially the QTC application-specific integrated circuit (ASIC), can be found in [79].…”

“…In this time, between the initial integration and the end of the veto, any other hits on that PMT will be ignored. From [79].…”

“…The upgraded system replaced the hardware trigger with a system where every hit is recorded, and a software system applies triggering. This hardware [79] allows for much higher data throughput, allowing for lower energy thresholds, or more complex triggering. Such special triggers can include neutron tagging for solar ν e events, and the T2K beam trigger.…”

Search for proton decay viap→νK+using260 kiloton·yeardata of Super-Kamiokande

“…Ikenoyama (2,700 m water equivalent underground) to reduce cosmic ray back- (31.9 kton·years), is defined as SK-III. In the summer of 2008, we upgraded our electronics with improved performance including a data acquisition that records all PMT hit information without dead time [15]. This has been the configuration of the detector since September 2008; it is called SK-IV.…”

Solar results from Super-Kamiokande

“…SK started in 1996 and the total live time of the solar neutrino analysis in this time is 4504 days. There are four experimental phases, and the latest SK-IV started in 2008 after new electronics (QBEE [6]) was installed. One of the most important progress for the solar neutrino measurement is a reduction of background thanks to the water system improvement.…”