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arxiv: 1907.02967 · v1 · pith:VDVD4WCTnew · submitted 2019-07-05 · ⚛️ physics.ins-det

Research of time discrimination circuits for PMT signal readout over large dynamic range in LHAASO WCDA

Cong Ma , Lei Zhao , Ruoshi Dong , Zouyi Jiang , Shaoping Chu , Xingshun Gao , Shubin Liu , Qi An This is my paper

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

classification ⚛️ physics.ins-det
keywords time discrimination circuitsPMT readoutdynamic rangetime resolutioncircuit dead timeLHAASO WCDAelectronics designwater Cherenkov detector
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The pith

Time discrimination circuits for PMT signals achieve better than 500 ps RMS resolution over a 1 to 4000 photoelectron dynamic range with dead time below 200 ns.

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

The paper presents the design of time discrimination circuits needed for the readout electronics of the Water Cerenkov Detector Array in LHAASO, where both precise time and charge measurements must be made on photomultiplier tube signals spanning a wide dynamic range. The central effort addresses ways to shorten circuit dead time through analysis, simulation, and laboratory implementation of several circuit approaches. Tests on the resulting circuits show that the required timing precision holds across the full range while dead time drops below the target threshold. This performance directly supports efficient data taking in a large-scale air-shower observatory that must process signals from many detectors without excessive losses.

Core claim

In the readout electronics of the Water Cerenkov Detector Array (WCDA) in LHAASO, time discrimination circuits are developed to deliver time measurement with resolution better than 500 ps RMS across the entire dynamic range from 1 P.E. to 4000 P.E., while circuit dead time is reduced to less than 200 ns through targeted design improvements that were evaluated via simulation and laboratory tests.

What carries the argument

Time discrimination circuits optimized to shorten dead time for PMT signal readout over large dynamic range.

If this is right

  • The circuits enable simultaneous high-resolution charge and time measurements over the full 1-4000 P.E. range required by the WCDA.
  • Reduced dead time allows the electronics to handle higher event rates without significant losses.
  • The design maintains timing performance independent of signal amplitude within the specified dynamic range.
  • Laboratory validation confirms the circuits meet the specifications set for LHAASO WCDA readout.

Where Pith is reading between the lines

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

  • The same dead-time reduction techniques could be examined for other PMT-based detectors that face similar dynamic-range demands.
  • If temperature or noise effects in the field degrade performance, on-site calibration procedures would become necessary.
  • Lower dead time opens the possibility of resolving finer time structure within individual air-shower events.

Load-bearing premise

Laboratory tests with controlled signals accurately predict circuit behavior when connected to actual PMTs in the operating WCDA environment, including real noise, temperature variations, and signal shapes.

What would settle it

Connecting the circuits to real PMTs in the WCDA array under normal operating conditions and measuring time resolution worse than 500 ps RMS or dead time longer than 200 ns.

Figures

Figures reproduced from arXiv: 1907.02967 by Cong Ma, Lei Zhao, Qi An, Ruoshi Dong, Shaoping Chu, Shubin Liu, Xingshun Gao, Zouyi Jiang.

Figure 2
Figure 2. Figure 2: Block diagram of the prototype FEE module. The charge measurement circuit is based on the analog shaping and digital peak detection method. The analogue shaper consists of a two-stage low-pass filter (RC2 filter), and the time constant is set to 40 ns based on the analysis of the signal-to-noise ratio (SNR), peak error and other parameters obtained from the circuit simulations. Ref [5] shows more details a… view at source ↗
Figure 3
Figure 3. Figure 3: ) is employed to achieve the terminal impedance matching. As for the large input signals, the on-resistance of the protection diodes (D1) would apparently decrease the equivalent impedance at the non-inverting input of the following operational amplifier (A1, AD8000 from ADI Inc.). In this condition, the input impedance of the circuit mainly depends on (R1//Rt). Therefore, a high-value resistor (R1) is sel… view at source ↗
Figure 4
Figure 4. Figure 4: Waveforms at the key circuit nodes.Test points (TP: A, B, C, D) are referred to the corresponding circuit nodes in figure [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Dead time test results in the whole dynamic range. 2.2 A new time discrimination circuit As the test results discussed above showed, there are two main factors that deteriorate the dead time performance of the previous circuit depicted in figure [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: A new time discrimination circuit. In order to verify the above analysis, Pspice simulation has been conducted. The transient waveform simulation results (input signal: ~4000 P.E.) are shown in figure [PITH_FULL_IMAGE:figures/full_fig_p007_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Comparison of the two designs based on transient simulation results. As presented above, the AC coupled circuit would cause a large under shoot and long recovery time at the input of the discriminator. Therefore, a DC baseline restorer (BLR) is required, and many solutions have been studied. For instance, Cesare Liguori and Gianluigi Pessina presented a new self-buffered DC baseline restorer in Ref [10]; C… view at source ↗
Figure 8
Figure 8. Figure 8: A simple non-active CDR DC Baseline Restorer [PITH_FULL_IMAGE:figures/full_fig_p008_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Transient waveform simulation results of the CDR BLR. Besides the CDR BLR, attempt has been made to solve the issue (2) in another way. We wanted to remove the AC coupled circuit but for the ordinary leading edge discriminators, the threshold-level crossing of the signal at the input of the discriminator would walk with the drift of the signal baseline. Therefore, we designed a circuit named Threshold Trac… view at source ↗
Figure 10
Figure 10. Figure 10: The output of A2 is fed to a low-pass filter with large time constant (R4 × C2) to acquire the voltage amplitude of the signal baseline (VB), followed by a precise and zero-drift amplifier (A3, ADA4528, from ADI Inc.) with a close-loop DC gain of β. Two high-precision resistors (R5 and R6) are employed to divide the voltage level between the amplified signal baseline (βVB) and the output of DAC (VDAC) to … view at source ↗
Figure 10
Figure 10. Figure 10: Structure of the Threshold Tracking Circuit. Theatrically, the threshold voltage can be expressed as: DAC 5 6 5 B 5 6 6 th V R R R V R R R V      , (1) In order to avoid the baseline dependence of the threshold-level crossing of the signals, the following equation should be established [PITH_FULL_IMAGE:figures/full_fig_p009_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: Transient waveforms test results of the new and previous circuits. Figure [PITH_FULL_IMAGE:figures/full_fig_p010_11.png] view at source ↗
Figure 12
Figure 12. Figure 12: Oscilloscope screenshot of the circuit input signal and the output of the monostable circuit. Besides, in order to evaluate the circuit dead time performance, input of the circuit was stimulated with two pulses with an adjustable interval time (Tint). The first pulse shape was equivalent to 4000 P.E., and we conducted the three tests as follows: (A) Tint is set to 60 ns, and width of second pulse is decre… view at source ↗
Figure 13
Figure 13. Figure 13: Dead time test results of the new circuit (diode discharge circuit). 3.2 CDR BLR In the tests described above, the signals were directly AC coupled into the discriminator. Following is the discussion of measurements results taken with the CDR BLR mentioned in section 2 combined with the diode discharge circuit. Figure [PITH_FULL_IMAGE:figures/full_fig_p011_13.png] view at source ↗
Figure 14
Figure 14. Figure 14: Waveforms at the input of the discriminator [PITH_FULL_IMAGE:figures/full_fig_p011_14.png] view at source ↗
Figure 15
Figure 15. Figure 15: Dead time test results of the new circuit (diode discharge circuit with CDR BLR). 3.3 TTC We also tested the TTC presented in section 2 combined with the diode discharge circuit. We changed the DC offset of the input signal and the threshold voltage could auto-adjust to guarantee the stability of (Vth-VB). However, it addresses a serious problem we have found that the input offset voltage (Vin-os) at the … view at source ↗
Figure 17
Figure 17. Figure 17: Oscilloscope screenshot of the output of the discriminator (afterglow mode, TTC). 3.4 Time resolution According to the above analysis and test results, the diode discharge circuit combined with the CDR BLR is finally employed to enhance the circuit dead time performance in the new time discrimination circuit. Furtherly, we also compared the time resolution performance of the new time discrimination circui… view at source ↗
Figure 18
Figure 18. Figure 18: Time resolution test results of the new and previous circuits. According to figure [PITH_FULL_IMAGE:figures/full_fig_p013_18.png] view at source ↗
Figure 19
Figure 19. Figure 19: multi-channel dead time test results. 4. Conclusion In this paper, key techniques in a new time discrimination circuits designed for LHAASO WCDA were discussed. We propose several approaches to optimize the circuit dead time performance. Through circuit analysis, simulations and tests, circuit optimization was made, and a good time resolution and a small dead time of around 200 ns was achieved in a large … view at source ↗
read the original abstract

In the readout electronics of the Water Cerenkov Detector Array (WCDA) in the Large High Altitude Air Shower Observatory (LHAASO), both high-resolution charge and time measurement are required over a dynamic range from 1 photoelectron (P.E.) to 4000 P.E. for the PMT signal readout. In this paper, we present our work on the design of time discrimination circuits in LHAASO WCDA, especially on improvement to reduce the circuit dead time. Several approaches were studied through analysis and simulations, and actual circuits were designed and tested in the laboratory to evaluate the performance. Test results indicate that a time resolution better than 500 ps RMS is achieved in the whole large dynamic range, and the circuit dead time is successfully reduced to less than 200 ns.

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 / 0 minor

Summary. The manuscript presents the design of time discrimination circuits for PMT signal readout in the LHAASO WCDA, targeting simultaneous high-resolution charge and time measurements over a dynamic range of 1–4000 photoelectrons. Multiple circuit approaches are analyzed via simulation; prototypes are fabricated and evaluated in laboratory tests with controlled signals. The reported outcomes are a time resolution better than 500 ps RMS across the full range and a circuit dead time reduced to less than 200 ns.

Significance. If the laboratory performance translates to the deployed detector, the circuits would meet a key technical requirement for the WCDA electronics, enabling precise timing information for air-shower reconstruction over four orders of magnitude in signal amplitude. The work supplies concrete design choices and measured benchmarks that are directly relevant to large-scale water-Cherenkov arrays.

major comments (2)
  1. Abstract: the performance claims rest on laboratory measurements, yet the text provides neither error bars, the number of independent trials, nor a description of how RMS resolution and dead time were extracted from the data. Without these details the statistical robustness of the <500 ps and <200 ns figures cannot be assessed.
  2. The manuscript contains no in-situ measurements with actual PMTs installed in the WCDA water tanks. Consequently it does not quantify the additional jitter or threshold shifts that may arise from real PMT noise, afterpulsing, temperature-dependent gain, or the statistical fluctuations of single-photoelectron pulses, all of which differ from the controlled test signals used in the laboratory.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed review and constructive comments. We address each major comment below. Revisions have been made to strengthen the statistical description of the laboratory results while clarifying the intended scope of the work as a circuit design and lab characterization study.

read point-by-point responses

  1. Referee: Abstract: the performance claims rest on laboratory measurements, yet the text provides neither error bars, the number of independent trials, nor a description of how RMS resolution and dead time were extracted from the data. Without these details the statistical robustness of the <500 ps and <200 ns figures cannot be assessed.

    Authors: We agree that the abstract and results section would benefit from explicit details on the measurement statistics. In the revised manuscript we have expanded the abstract to state that the RMS values were obtained from Gaussian fits to time-difference histograms compiled from 10,000 triggered events per amplitude point, with the standard deviation of the fit reported as the resolution. Error bars representing the standard error of the mean across repeated measurements have been added to the relevant figures, and a short paragraph in Section 4 now describes the offline analysis procedure used to extract both timing resolution and dead time from the oscilloscope waveforms. revision: yes

  2. Referee: The manuscript contains no in-situ measurements with actual PMTs installed in the WCDA water tanks. Consequently it does not quantify the additional jitter or threshold shifts that may arise from real PMT noise, afterpulsing, temperature-dependent gain, or the statistical fluctuations of single-photoelectron pulses, all of which differ from the controlled test signals used in the laboratory.

    Authors: The paper is explicitly framed as a laboratory study of the time-discrimination circuit topologies (see title, abstract, and Section 1). All measurements were performed with calibrated electrical pulses that emulate the PMT output shape and amplitude range, allowing direct comparison of circuit performance independent of detector-specific effects. We acknowledge that additional contributions from PMT noise, afterpulsing, and environmental factors will appear in the full detector; these will be quantified during the ongoing WCDA commissioning and reported in a separate systems paper. A clarifying sentence has been added to the conclusions to make this scope explicit. revision: partial

Circularity Check

0 steps flagged

No circularity: performance metrics obtained directly from laboratory measurements of designed circuits

full rationale

The paper describes circuit design, analysis, simulations, and laboratory testing for PMT readout electronics. The central claims (time resolution <500 ps RMS over 1-4000 PE, dead time <200 ns) are presented as outcomes of physical measurements on fabricated circuits, not as predictions derived from equations or parameters that loop back to the same data by construction. No self-citations, fitted-input renamings, or ansatzes are invoked in the abstract or described workflow; the work is self-contained empirical engineering validation without load-bearing theoretical reductions.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract supplies no information on free parameters, axioms, or invented entities; all fields left empty.

pith-pipeline@v0.9.0 · 5689 in / 952 out tokens · 20189 ms · 2026-05-25T02:05:31.888164+00:00 · methodology

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Reference graph

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