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arxiv: 1907.02966 · v1 · pith:JBAS34CHnew · submitted 2019-07-05 · ⚛️ physics.ins-det

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

Lei Zhao , Weihao Wu , Jianfeng Liu , Yu Liang , Jiajun Qin , Li Yu , Shubin Liu , Qi An This is my paper

Pith reviewed 2026-05-25 02:13 UTC · model grok-4.3

classification ⚛️ physics.ins-det
keywords ASICfront-end readoutcharge-to-time conversionWater Cherenkov DetectorLHAASOtime resolutionphotomultiplier tubedynamic range
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The pith

Prototype ASIC for LHAASO water Cherenkov array reaches time resolution better than 0.5 ns over 1 to 4000 photoelectrons.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper describes the design and initial bench testing of a front-end readout ASIC for photomultiplier tube signals in the Water Cherenkov Detector Array of LHAASO. Signals span a wide dynamic range from single photoelectrons to 4000, and the design uses charge-to-time conversion to encode both charge and timing information into pulse widths that can be digitized together with external TDCs. This approach simplifies the overall readout chain. Bench tests on the 0.35 micrometer CMOS prototype show time resolution better than 0.5 ns across the full range and charge resolution better than 15 percent at the single-photoelectron level, exceeding the stated requirements for the observatory.

Core claim

The prototype ASIC integrates time discrimination and charge-to-time conversion so that both time and charge are digitized simultaneously; bench tests confirm time resolution better than 0.5 ns from 1 to 4000 photoelectrons (0.75 to 3000 pC) and charge resolution better than 1 percent for large amplitudes and better than 15 percent at one photoelectron, with a 0.188 pC threshold.

What carries the argument

Charge-to-time conversion circuit that maps input charge to output pulse width for simultaneous digitization of time and charge information.

If this is right

  • The ASIC meets or exceeds the dynamic-range, timing, and charge-precision needs of the LHAASO water Cherenkov detectors.
  • Charge and time information are captured in a single pulse-width measurement, removing the need for separate analog charge and timing paths.
  • The 0.35 micrometer CMOS implementation is compatible with existing Time-to-Digital Converters for full digitization.
  • Performance holds across the full 1 to 4000 photoelectron range required for air-shower detection.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The charge-to-time method could reduce power and complexity in other large-area detector arrays that need wide dynamic range.
  • Further integration of the TDC on the same die might lower overall system latency and jitter.
  • Calibration procedures developed for this ASIC could transfer to similar readout chips in future neutrino or cosmic-ray experiments.

Load-bearing premise

Bench-test conditions with controlled charge injection accurately represent the noise, rate, and signal shape expected from real photomultiplier tubes operating inside the Water Cherenkov Detector Array.

What would settle it

Measure time and charge resolution when the ASIC is driven by actual photomultiplier tube pulses from the Water Cherenkov Detector Array under normal operating rates and backgrounds; deviation beyond the reported resolutions would falsify the performance claim.

Figures

Figures reproduced from arXiv: 1907.02966 by Jiajun Qin, Jianfeng Liu, Lei Zhao, Li Yu, Qi An, Shubin Liu, Weihao Wu, Yu Liang.

Figure 9
Figure 9. Figure 9: figure 9. By adjusting the sizes of the MOSFETs, a delay less than 1 ns is achieved with a step [PITH_FULL_IMAGE:figures/full_fig_p007_9.png] view at source ↗
read the original 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.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The manuscript presents the design of a prototype front-end readout ASIC fabricated in Chartered 0.35 μm CMOS technology for the Water Cherenkov Detector Array (WCDA) in LHAASO. The ASIC employs charge-to-time conversion to measure PMT signals spanning 1 to 4000 photoelectrons (0.75 to 3000 pC), enabling simultaneous time and charge digitization when paired with TDCs. Initial bench tests with controlled charge injection are reported to achieve time resolution better than 0.5 ns across the full dynamic range and charge resolution better than 1% for 500–4000 PE inputs, remaining better than 15% at 1 PE, exceeding the stated application requirements.

Significance. If the reported resolutions hold under actual WCDA operating conditions, the work provides a practical ASIC solution that simplifies the readout chain for a large-scale water Cherenkov array by integrating time discrimination and charge-to-time conversion in a single chip.

major comments (2)
  1. [Abstract and test-results section] Abstract and test-results section: the headline performance claims (time resolution <0.5 ns; charge resolution <1% at high amplitudes and <15% at 1 PE) are presented without error bars, number of trials, statistical analysis, or raw data, preventing independent assessment of the reliability of the central experimental results.
  2. [Bench-test description] Bench-test description: no quantitative comparison or auxiliary data are supplied to establish that the controlled charge-injection conditions reproduce the noise floor, event rates, and PMT pulse shapes expected inside the WCDA; this equivalence is load-bearing for the assertion that the measured resolutions meet application requirements in the real detector.
minor comments (1)
  1. [Abstract] Typo: 'disctrimination' should read 'discrimination'.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the thorough review and constructive feedback on our manuscript describing the prototype front-end readout ASIC. We address the major comments point by point below and will revise the manuscript to strengthen the presentation of results and test methodology.

read point-by-point responses

  1. Referee: [Abstract and test-results section] Abstract and test-results section: the headline performance claims (time resolution <0.5 ns; charge resolution <1% at high amplitudes and <15% at 1 PE) are presented without error bars, number of trials, statistical analysis, or raw data, preventing independent assessment of the reliability of the central experimental results.

    Authors: We agree that the abstract and results section would benefit from additional statistical details to allow independent assessment. The reported time and charge resolutions are based on repeated bench measurements, but the current manuscript does not include error bars, the number of trials, or explicit statistical analysis. In the revised version we will add error bars to the relevant figures, state the number of measurements performed for each data point, and include a short description of the statistical treatment used to derive the quoted resolutions. revision: yes

  2. Referee: [Bench-test description] Bench-test description: no quantitative comparison or auxiliary data are supplied to establish that the controlled charge-injection conditions reproduce the noise floor, event rates, and PMT pulse shapes expected inside the WCDA; this equivalence is load-bearing for the assertion that the measured resolutions meet application requirements in the real detector.

    Authors: The bench tests employed a standard charge-injection setup calibrated to cover the full 1–4000 PE dynamic range with pulse amplitudes and widths chosen to approximate typical PMT signals. We acknowledge that the manuscript does not supply quantitative comparisons (e.g., measured noise spectra or event-rate simulations) demonstrating exact equivalence to the WCDA environment. As this is a prototype ASIC paper, such system-level validation lies outside the present scope; we will add a dedicated paragraph in the test section explaining the design choices for the injection circuit and noting that full equivalence testing will be addressed in future integrated-detector studies. revision: partial

Circularity Check

0 steps flagged

No circularity; experimental results reported directly from bench tests

full rationale

The manuscript describes ASIC design and reports measured time/charge resolutions from controlled charge-injection bench tests. No equations, derivations, fitted parameters, or predictions are present. Claims rest on direct experimental data rather than any self-referential chain, self-citation load-bearing step, or ansatz. This is the normal non-circular outcome for a pure instrumentation paper.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This is an experimental hardware design paper; it contains no mathematical derivations, free parameters fitted to data, background axioms, or postulated physical entities.

pith-pipeline@v0.9.0 · 5772 in / 1116 out tokens · 24496 ms · 2026-05-25T02:13:28.343670+00:00 · methodology

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Reference graph

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