Waveform Sampling Research Articles

Front-end electronic readout system for the Belle II imaging Time-Of-Propagation detector

The Time-Of-Propagation detector is a Cherenkov particle identification detector based on quartz radiator bars for the Belle II experiment at the SuperKEKB electron-positron collider. The purpose of the detector is to identify the type of charged hadrons produced in electron-positron collisions, and requires a single photon timing resolution below 100 picoseconds. A novel front-end electronic system was designed, built, and integrated to acquire data from the 8192 microchannel plate photomultiplier tube channels in the detector. Waveform sampling of these analog signals is done by switched-capacitor array application-specific integrated circuits. The processes of triggering, digitization of windows of interest, readout, and data transfer to the Belle II data acquisition system are managed by Xilinx Zynq-7000 programmable system on a chip devices.

Performance of the Belle II imaging Time-Of-Propagation (iTOP) detector in first collisions

The iTOP detector is a novel Cherenkov detector developed for barrel particle identification at Belle II, an upgrade of the previous Belle experiment at KEK. The SuperKEKB accelerator, an upgrade of KEKB, collides electrons and positrons with a design luminosity of 8⋅1035cm−2s−1. In order to exploit the high collision rate, Belle II has a trigger frequency of up to 30 kHz. The iTOP detector uses quartz bars as source of Cherenkov photons. The photons are reflected inside the bars until they hit photomultipliers at one end. The spatial distribution and precise arrival times of the detected photons are used to reconstruct the Cherenkov angle. The photon arrival times have to be measured with a resolution better than 100 ps to achieve a good pion–kaon separation. Microchannel plate photomultipliers together with dedicated high-speed electronics for 2.7 GSa/s waveform sampling are used to achieve this timing resolution. The iTOP detector consists of 16 modules with 512 channels each, in total the detector has 8192 channels. First collisions were recorded in spring 2018. A phase of physics operation with a ramp up to full luminosity starts in March 2019. The design of the iTOP detector is shown and experience and results from initial operation are discussed together with an outlook on future running conditions.

Statistical properties of hybrid estimators proposed for GEDI—NASA’s global ecosystem dynamics investigation

NASA’s Global Ecosystem Dynamics Investigation (GEDI) mission will collect waveform lidar data at a dense sample of ∼25 m footprints along ground tracks paralleling the orbit of the International Space Station (ISS). GEDI’s primary science deliverable will be a 1 km grid of estimated mean aboveground biomass density (Mg ha−1), covering the latitudes overflown by ISS (51.6 °S to 51.6 °N). One option for using the sample of waveforms contained within an individual grid cell to produce an estimate for that cell is hybrid inference, which explicitly incorporates both sampling design and model parameter covariance into estimates of variance around the population mean. We explored statistical properties of hybrid estimators applied in the context of GEDI, using simulations calibrated with lidar and field data from six diverse sites across the United States. We found hybrid estimators of mean biomass to be unbiased and the corresponding estimators of variance appeared to be asymptotically unbiased, with under-estimation of variance by approximately 20% when data from only two clusters (footprint tracks) were available. In our study areas, sampling error contributed more to overall estimates of variance than variability due to the model, and it was the design-based component of the variance that was the source of the variance estimator bias at small sample sizes. These results highlight the importance of maximizing GEDI’s sample size in making precise biomass estimates. Given a set of assumptions discussed here, hybrid inference provides a viable framework for estimating biomass at the scale of a 1 km grid cell while formally accounting for both variability due to the model and sampling error.

Analysis of Regular Sampling of Chaotic Waveform and Chaotic Sampling of Regular Waveform for Random Number Generation

Analysis of Regular Sampling of Chaotic Waveform and Chaotic Sampling of Regular Waveform for Random Number Generation

Single-Event-Hardened Timing Generator for waveform digitizer based readout electronics

Waveform digitizer, the soul of readout electronics in the radiation detectors performing a multitude of functions has to evade the impact of single-event transients in its timing reference. The propagation of transients from the timing generator to the analog memory causes timing non-linearity due to variation in the inverter delay responsible for the sampling speed leading to catastrophic failure of the waveform sampler. The presented timing generator using mixed-signal delay-locked loop implements the triple combination of the body-feed technique allowing rail-to-rail operation for delay control, the pseudo differential structure regulating duty cycle reduces the jitter and also optimize the linear operating range of the voltage-controlled-delay-line, and the mixed-signal delay-locked loop embedded with dual-edge synchronization enhances the mitigation of single-event upsets. The simulation results at the circuit level using 180 nm and 90 nm CMOS PDKs show a 28% increase in the linear operating range and bettering jitter performance of the mixed-signal delay-locked loop in comparison to the fully differential voltage-controlled-delay-line based delay-locked loop. Furthermore, there is only negligible variance between the irradiated and non-irradiated values for delay interval of each sampling cell and cell-to-cell gain variation in the analog memory of the waveform sampler.

Particle identification in the Belle II experiment

The Belle II experiment integrates two dedicated particle identification (PID) subdetectors for pion/kaon separation. The Aerogel Ring Image Cherenkov (ARICH) detector is a forward region PID detector based on two layers of aerogel read out by hybrid avalanche photo detectors. The Time of Propagation (TOP) detector is a novel Cherenkov barrel PID system built for the Belle II detector upgrade based on quartz radiator bars read out by Micro-Channel Plate PMTs. The readout electronics of the TOP system are built around a switched capacitor array waveform sampling ASIC operating at 2.7 GSa/s. Acquired waveforms are processed in real time in the front-end electronics, extracting the individual timing of detected photons to better than 100 ps. This contribution presents the concept of the Belle II particle identification systems with a focus on the current status of commissioning, calibration and operation of the Belle II TOP detector.

Gravitational wave emission from 3D explosion models of core-collapse supernovae with low and normal explosion energies

Understanding gravitational wave emission from core-collapse supernovae will be essential for their detection with current and future gravitational wave detectors. This requires a sample of waveforms from modern 3D supernova simulations reaching well into the explosion phase, where gravitational wave emission is expected to peak. However, recent waveforms from 3D simulations with multi-group neutrino transport do not reach far into the explosion phase, and some are still obtained from non-exploding models. We therefore calculate waveforms up to 0.9\,s after bounce using the neutrino hydrodynamics code \textsc{CoCoNuT-FMT}. We consider two models with low and normal explosion energy, namely explosions of an ultra-stripped progenitor with an initial helium star mass of $3.5\,M_{\odot}$, and of an $18\,M_{\odot}$ single star. Both models show gravitational wave emission from the excitation of surface g-modes in the proto-neutron star with frequencies between $\mathord{\sim}800\,\mathrm{Hz}$ and 1000\,Hz at peak emission. The peak amplitudes are about $6\, \mathrm{cm}$ and $10\, \mathrm{cm}$, respectively, which is somewhat higher than in most recent 3D models of the pre-explosion or early explosion phase. Using a Bayesian analysis, we determine the maximum detection distances for our models in simulated Advanced LIGO, Advanced Virgo, and Einstein Telescope design sensitivity noise. The more energetic $18 M_\odot$ explosion will be detectable to about $17.5 \,\mathrm{kpc}$ by the LIGO/Virgo network and to about $180\, \mathrm{kpc}$ with the Einstein Telescope.

Development of high-performance multichannel analyzer by using traditional pulse forming method and high-speed waveform sampling technology

A high performance multichannel analyzer (MCA) based on traditional used pulse forming method and high-speed waveform sampling technology was developed in this paper for spectra analysis and radioactive measurement. The self-developed MCA is composed of conditioning part and processing part. The conditioning part including pole-zero cancellation, polarity conversion, programmable amplification, active integral filter, baseline recovery and peak holding is adopted to realize amplification, Gauss shaping and peak holding functions, while the processing part mainly including dither circuit, 16-bit 100 MHz high speed ADC and FPGA is employed to make waveform sampling and spectra acquisition. The performance including the differential nonlinearity (DNL), integral nonlinearity (INL) and energy resolution are studied by using precision sliding pulse generator, NaI scintillator detector and radiation sources. The results show that the DNL and INL of the MCA are better than 1.06% and 0.09% respectively, and the energy resolution measured with NaI scintillator detector at 0.662 MeV is about 7.82%. In addition, the DNL value depends on the appropriate selection of dither channels, and the optimal dither channel is 64 for the self-developed MCA in this paper. At last, the overall performance of the self-developed MCA is compared with a commercially available NIM plug-in type MCA, the results indicate that the MCA designed in this paper is obviously better than the commercially available MCA.

Watt-scale 50-MHz source of single-cycle waveform-stable pulses in the molecular fingerprint region.

We report a coherent mid-infrared (MIR) source with a combination of broad spectral coverage (6-18 μm), high repetition rate (50 MHz), and high average power (0.5 W). The waveform-stable pulses emerge via intrapulse difference-frequency generation (IPDFG) in a GaSe crystal, driven by a 30-W-average-power train of 32-fs pulses spectrally centered at 2 μm, delivered by a fiber-laser system. Electro-optic sampling (EOS) of the waveform-stable MIR waveforms reveals their single-cycle nature, confirming the excellent phase matching both of IPDFG and of EOS with 2-μm pulses in GaSe.

FPGA-Based Real-Time <inline-formula> <tex-math notation="LaTeX">$n/\gamma$ </tex-math> </inline-formula> Discrimination With Liquid Scintillator

A real-time $n/\gamma $ discrimination prototype system based on high-speed waveform sampling and high-performance field-programmable gate array (FPGA) is presented in this paper. In order to accurately record detector signals, a high-speed sampling board with a 14-bit analog-to-digital converter (AD9680) is designed. The BC501A liquid scintillator is employed as the neutron detector, and a discrimination algorithm is implemented in the FPGA of the sampling board. The system is calibrated by 22Na, 137Cs, and 60Co $\gamma $ -sources. A PuC neutron source is used to evaluate the discrimination ability. The figure-of-merit of PuC neutron source is determined to be about 1.005 over an energy range of 0–4000 keVee, which is consistent with the test results of the commercial digitizer, and the false alarm rate of 60Co is 0.19%. This system has been successfully applied for the environmental neutron monitoring experiment during the first commissioning of white neutron source tunnel of China spallation neutron source.

An overdetermined linear equations-based time calibration method for fast sampling ASICs

A novel time calibration method for waveform sampling application specific integrated circuits (ASICs) based on switched capacitor arrays (SCAs) is proposed in this paper. Precision timing extraction using SCA ASICs has been proved to be a promising technique in many high energy physics experiments. However, such ASICs suffer from irregular sampling intervals caused by process variations. Therefore, careful calibration is required to improve the time resolution of such systems. We evaluated the limitation of a popular method using the proportionality between voltage amplitude and sampling interval of adjacent switched-capacitor cells responding to either a sawtooth wave or a sine wave. The new time calibration method presented here utilizes the relationship between sampling intervals and the known input signal period to establish overdetermined linear equations, and the roots of these equations correspond to the actual sampling intervals. We applied this new method to a pulse timing test with an ASIC designed by our team, and the test results indicate that the new time calibration method is effective.

The investigation of a new fast timing system based on DRS4 waveform sampling system

Abstract In the study of nuclear structure, the fast timing technique can be used to measure the lifetime of excited states. In the paper, we have developed a new fast timing system, which is made up of two LaBr3:Ce detectors and a set of waveform sampling system. The sampling system based on domino ring sampler version 4 chip (DRS4) can digitize and store the waveform information of detector signal, with a smaller volume and higher timing accuracy, and the waveform data are performed by means of digital waveform analysis methods. The coincidence time resolution of the fast timing system for two annihilation 511 keV γ photon is 200ps (FWHM), the energy resolution is 3.5%@511 keV, and the energy linear response in the large dynamic range is perfect. Meanwhile, to verify the fast timing performance of the system, the 152Gd-21+ state form β+ decay of 152Eu source is measured. The measured lifetime is 45.3(±5.0)ps, very close to the value of the National Nuclear Data Center (NNDC: 46.2((±3.9)ps). The experimental results indicate that the fast timing system is capable of measuring the lifetime of dozens of ps. Therefore, the system can be widely used in the research of the fast timing technology.

PhaseNet: A Deep-Neural-Network-Based Seismic Arrival Time Picking Method

As the number of seismic sensors grows, it is becoming increasingly difficult for analysts to pick seismic phases manually and comprehensively, yet such efforts are fundamental to earthquake monitoring. Despite years of improvements in automatic phase picking, it is difficult to match the performance of experienced analysts. A more subtle issue is that different seismic analysts may pick phases differently, which can introduce bias into earthquake locations. We present a deep-neural-network-based arrival-time picking method called that picks the arrival times of both P and S waves. Deep neural networks have recently made rapid progress in feature learning, and with sufficient training, have achieved super-human performance in many applications. PhaseNet uses three-component seismic waveforms as input and generates probability distributions of P arrivals, S arrivals, and noise as output. We engineer PhaseNet such that peaks in probability provide accurate arrival times for both P and S waves, and have the potential to increase the number of S-wave observations dramatically over what is currently available. This will enable both improved locations and improved shear wave velocity models. PhaseNet is trained on the prodigious available data set provided by analyst-labeled P and S arrival times from the Northern California Earthquake Data Center. The dataset we use contains more than seven million waveform samples extracted from over thirty years of earthquake recordings. We demonstrate that PhaseNet achieves much higher picking accuracy and recall rate than existing methods.

Monolithic sensors in LFoundry technology: Concepts and measurements

Abstract In the LFoundry LF15A 150 nm HVCMOS process, detector chips with several matrices were developed and produced on different resistivity substrates for process evaluation. These matrices focus on different aspects offering innovative approaches including grouped readout and waveform sampling. Both grouped readout and waveform sampling were demonstrated to work for reducing readout bandwidth with triggering and cluster readout in first case and offline post-processing in second case.

Waveform Modeling and Generation Using Hierarchical Recurrent Neural Networks for Speech Bandwidth Extension

This paper presents a waveform modeling and generation method using hierarchical recurrent neural networks (HRNN) for speech bandwidth extension (BWE). Different from conventional BWE methods which predict spectral parameters for reconstructing wideband speech waveforms, this BWE method models and predicts waveform samples directly without using vocoders. Inspired by SampleRNN which is an unconditional neural audio generator, the HRNN model represents the distribution of each wideband or high-frequency waveform sample conditioned on the input narrowband waveform samples using a neural network composed of long short-term memory (LSTM) layers and feed-forward (FF) layers. The LSTM layers form a hierarchical structure and each layer operates at a specific temporal resolution to efficiently capture long-span dependencies between temporal sequences. Furthermore, additional conditions, such as the bottleneck (BN) features derived from narrowband speech using a deep neural network (DNN)-based state classifier, are employed as auxiliary input to further improve the quality of generated wideband speech. The experimental results of comparing several waveform modeling methods show that the HRNN-based method can achieve better speech quality and run-time efficiency than the dilated convolutional neural network (DCNN)-based method and the plain sample-level recurrent neural network (SRNN)-based method. Our proposed method also outperforms the conventional vocoder-based BWE method using LSTM-RNNs in terms of the subjective quality of the reconstructed wideband speech.

Signal Detection Under Short-Interval Sampling of Continuous Waveforms for Optical Wireless Scattering Communication

In optical wireless scattering communication, the received signal in each symbol interval is captured by a photomultiplier tube and then sampled through very short but finite interval sampling. The resulting samples form a signal vector for symbol detection. The upper and lower bounds on transmission rate of such a processing system are studied. It is shown that the gap between two bounds approaches zero as the thermal noise and shot noise variances approach zero. In order to reduce the computational cost in maximum a posteriori (MAP) receiver, the threshold-based signal detection is also studied, where two threshold selection rules are proposed based on the detection error probability and the Kullback–Leibler (KL) distance. For the latter, it is shown that the KL distance is not sensitive to the threshold selection for small shot and thermal noise variances, and thus, the threshold can be selected among a wide range without significant loss from the optimal KL distance. The performances of the transmission rate bounds, the signal detection, and the threshold selection approaches are evaluated by the numerical results.

The high-speed after-pulse measurement system for PMT

A system employing a desktop FADC has been developed to investigate the features of 8-inch Hamamatsu PMT R5912. The system stands out for its high-speed and informative results as a consequence of adopting fast waveform sampling technology. Recording the full waveforms allows us to perform pulse shape analysis. High-precision after-pulse time and charge distribution results are presented in this manuscript. Other characteristics of the photomultiplier tube, such as the gain of charge, dark rate and transit time spread, can be also obtained by this system.

Prototype readout system for a multi Mpixels UV single-photon imaging detector capable of space flight operation

Our collaboration works on the development of a large aperture, high resolution, UV single-photon imaging detector, funded through NASA's Strategic Astrophysics Technology (SAT) program. The detector uses a microchannel plate for charge multiplication, and orthogonal cross strip (XS) anodes for charge readout. Our target is to make an advancement in the technology readiness level (TRL), which enables real scale prototypes to be tested for future NASA missions. The baseline detector has an aperture of 50×50 mm and requires 160 low-noise charge-sensitive channels, in order to extrapolate the incoming photon position with a spatial resolution of about 20 μm FWHM. Technologies involving space flight require highly integrated electronic systems operating at very low power. We have designed two ASICs which enable the construction of such readout system. First, a charge sensitive amplifier (CSAv3) ASIC provides an equivalent noise charge (ENC) of around 600 e−, and a baseline gain of 10 mV/fC. The second, a Giga Sample per Second (GSPS) ASIC, called HalfGRAPH, is a 12-bit analog to digital converter. Its architecture is based on waveform sampling capacitor arrays and has about 8 μs of analog storage memory per channel. Both chips encapsulate 16 measurement channels. Using these chips, a small scale prototype readout system has been constructed on a FPGA Mezzanine Board (FMC), equipped with 32 measurement channels for system evaluation. We describe the construction of HalfGRAPH ASIC, detector's readout system concept and obtained results from the prototype system. As part of the space flight qualification, these chips were irradiated with a Cobalt gamma-ray source, to verify functional operation under ionizing radiation exposure.

Optimal design of waveform digitisers for both energy resolution and pulse shape discrimination

Fast digitisers and digital pulse processing have been widely used for spectral application and pulse shape discrimination (PSD) owing to their advantages in terms of compactness, higher trigger rates, offline analysis, etc. Meanwhile, the noise of readout electronics is usually trivial for organic, plastic, or liquid scintillator with PSD ability because of their poor intrinsic energy resolution. However, LaBr3(Ce) has been widely used for its excellent energy resolution and has been proven to have PSD ability for alpha/gamma particles. Therefore, designing a digital acquisition system for such scintillators as LaBr3(Ce) with both optimal energy resolution and promising PSD ability is worthwhile. Several experimental research studies about the choice of digitiser properties for liquid scintillators have already been conducted in terms of the sampling rate and vertical resolution. Quantitative analysis on the influence of waveform digitisers, that is, fast amplifier (optional), sampling rates, and vertical resolution, on both applications is still lacking. The present paper provides quantitative analysis of these factors and, hence, general rules about the optimal design of digitisers for both energy resolution and PSD application according to the noise analysis of time-variant gated charge integration.

Design of readout electronics based on peak-holding circuit and multiplexer for a fast neutron spectrometer

Fast neutron detection is meaningful in many research fields such as space environment monitoring. A scintillating fiber array model for fast neutron detection was proposed and developed in 1980s. Aerospace applications of the model require electronics in small size. To design a dedicated electronic system to readout and process the 384-channel signals from scintillating fiber array, and to use the designed system to fabricate a neutron detector for aerospace applications. With the method of nuclear recoil, fast neutron is detected by tracking recoil proton of n–p scatter in scintillating plastic fibers. Using the peak-holding circuits and multiplexers, the system size and power consumption were reduced. The detector fabricated with the designed system, had 34 cm $$\times $$ 34 cm $$\times $$ 27 cm mechanical size, 20.4 kg weight, and 30.05 W power consumption. Comparing to traditional waveform sampling electronics, the designed electronics was highly integrated and had a small size. The readout electronics also gave a better energy resolution of 39% in neutron detection, while the energy resolution was 43% in previous version. In this study, a highly integrated readout electronic system was designed and verified. The detector using the system gave good performance. The designed electronics had potential development in fast neutron detection and other high energy physics detection system.