ADC Sampling Research Articles

Impact of ADC Sampling Speed and Resolution on Uncompensated Long-Haul 111-Gb/s WDM PM-QPSK Systems

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We analyzed the effect of analog-to-digital conversion on the performance of polarization-multiplexed quadrature phase-shift keying at 111 Gb/s. We address analog-to-digital converter sampling speed, resolution, and clipping, taking into account both linear and nonlinear propagation effects over a 20-span uncompensated wavelength-division-multiplexing long-haul test-link with 50-GHz channel spacing, using either standard single-mode fiber or nonzero dispersion-shifted fiber. We assumed realistic optical and electrical filters. We found that penalty can be limited within 0.5 and 0.8 dB, if at least 5 bits of resolution and 1.6 or 1.5 samples per symbol are used, respectively. </para>

SU‐EE‐A1‐01: Development of a System to Measure Neutron Microdosimetry Spectra in a Mixed Proton‐Neutron Field

Purpose: To develop a miniature tissue‐equivalent proportional counter (TEPC), timing‐coincidence veto, and pulse‐height analysis system for the purpose of measuring neutron Microdosimetry spectra in a proton beam. Method and Materials: TEPC's were constructed with active volume geometry consisting of a 2.5mm right circular cylinder and employing a 10μm diameter stainless steel wire as the detector anode centered on the axis of an A150 tissue‐equivalent plastic cylinder with 2mm thick wall. Stainless steel field tubes define the active volume which is filled with propane based tissue‐equivalent gas to 168torr simulating a tissue density volume with 2μm diameter. Two fully depleted transmission‐type silicon detectors with diameter of 31.6mm will be operated in timing coincidence with the proportional counter as a charged particle veto system. Detector pulses are digitized in a 60MS/s sampling ADC and the data acquisition software is written in the LabVIEW graphical programming language which acquires and writes pulse waveforms to disk where pulse heights and timing information are extracted for further analysis. Results: A TEPC was tested in a mixed field produced in a proton treatment room with the proton beam incident on a closed tungsten MLC. The timing and energy resolutions for the TEPCs can be estimated from alpha spectra taken with a FWT LET‐1/2 detector attached to the data acquisition system. Timing and lineal energy resolution for the TEPCs are estimated to be 200ns and &gt;15keV/μm, respectively. Conclusion: Preliminary testing shows that the TEPC and silicon detector timing‐coincidence veto system is a viable method for extracting neutron Microdosimetry spectra from the mixed fields present in a proton therapy treatment room. This work was supported by the US Army Medical Research and Materiel Command under Contract Agreement No. DAMD17‐W81XWH‐07‐2‐0121. Opinions, interpretations, conclusions and recommendations are those of the author and are not necessarily endorsed by the US Army.

Digital pulse-shape discrimination of fast neutrons and [formula omitted] rays

Discrimination of the detection of fast neutrons and γ rays in a liquid scintillator detector has been investigated using digital pulse-processing techniques. An experimental setup with a 252Cf source, a BC-501 liquid scintillator detector, and a BaF 2 detector was used to collect waveforms with a 100 Ms/s, 14 bit sampling ADC. Three identical ADCs were combined to increase the sampling frequency to 300 Ms/s. Four different digital pulse-shape analysis algorithms were developed and compared to each other and to data obtained with an analogue neutron– γ discrimination unit. Two of the digital algorithms were based on the charge comparison method, while the analogue unit and the other two digital algorithms were based on the zero-crossover method. Two different figure-of-merit parameters, which quantify the neutron– γ discrimination properties, were evaluated for all four digital algorithms and for the analogue data set. All of the digital algorithms gave similar or better figure-of-merit values than what was obtained with the analogue setup. A detailed study of the discrimination properties as a function of sampling frequency and bit resolution of the ADC was performed. It was shown that a sampling ADC with a bit resolution of 12 bits and a sampling frequency of 100 Ms/s is adequate for achieving an optimal neutron– γ discrimination for pulses having a dynamic range for deposited neutron energies of 0.3–12 MeV. An investigation of the influence of the sampling frequency on the time resolution was made. A FWHM of 1.7 ns was obtained at 100 Ms/s.

0.5-$\mu\hbox{m}$ CMOS Implementation of Analog Heart-Rate Extraction With a Robust Peak Detector

A robust high-accuracy analog-signal-processing 0.5-mum CMOS chip for real-time heart-rate (HR) extraction is presented. A novel peak-detector architecture is proposed and implemented to facilitate on-chip integration. The system is capable of processing electrocardiogram (ECG) signals with a peak-to-peak amplitude as low as 5 mV, without any prefiltering. Experimental results with prerecorded and real-time ECG signals have demonstrated the obtained R-R interval accuracy on the order of milliseconds. The system was also used to successfully extract HR intervals with Doppler radar. Such a system may significantly reduce ADC resolution and sampling speed requirements while providing high immunity to noise and DC offset drift.

Use of single photon counting detector arrays in combined PET/MR: Characterization of LYSO-SiPM detector modules and comparison with a LSO-APD detector

We propose in this study a novel PET detector concept asinsert for simultaneous PET/MR imaging, using arrays of SiliconPhotomultipliers (SiPMs) as photodetectors, read out by a dataacquisition system based on sampling ADCs. A 2 × 2 LSO-SiPMdetector array and four single channel LYSO-SiPM detectors have beenevaluated and compared to a LSO-APD detector. A 17.9% energyresolution and a 1.4 ns time resolution have been measured. Nodegradation of these values could be detected when simultaneous MRacquisitions were performed. The non-linear detector behaviour due tothe limited dynamic range and recovery time effects has beenstudied. In addition, the contribution of dark counts and opticalcrosstalk for PET applications was also addressed. The feasibility forposition localization of the incident light to a SiPM array usingAnger logic has been investigated.

A CMOS Ultra-Wideband Receiver for Low Data-Rate Communication

A low-power impulse-radio ultra-wideband receiver is demonstrated for low data-rate applications. A topology selection study demonstrates that the quadrature analog correlation is a good receiver architecture choice when energy consumption must be minimized. The receiver operates in the 3.1-5 GHz band of the UWB FCC spectrum mask on channels of 500 MHz bandwidth. The pulse correlation operation is done in the analog domain in order to reduce the ADC sampling speed down to the pulse repetition rate, thereby reducing the power consumption. The receiver comprises a low-noise amplifier with full on-chip matching network, an RF local oscillator generation, two quadrature mixers, two analog baseband chains followed by two ADCs, and a clock generation network. The receiver is implemented in 0.18 mum CMOS technology and achieves 16 mA power consumption at 20 Mpulses/s pulse repetition rate.

Fast photon detection for the COMPASS RICH detector

Particle identification at high rates is a central aspect of many present and future experiments in high-energy particle physics. The COMPASS experiment at the SPS accelerator at CERN uses a large scale Ring Imaging CHerenkov detector (RICH) to identify pions, kaons and protons in a wide momentum range. For the data taking in 2006, the COMPASS RICH has been upgraded in the central photon detection area (25% of the surface) with a new technology to detect Cherenkov photons at very high count rates of several 10 6 s −1 per channel and a new dead-time free read-out system, which allows trigger rates up to 100 kHz. The Cherenkov photons are detected by an array of 576 visible and ultra-violet sensitive multi-anode photomultipliers with 16 channels each. Lens telescopes of fused silica lenses have been designed and built to focus the Cherenkov photons onto the individual photomultipliers. The read-out electronics of the PMTs is based on the MAD4 amplifier-discriminator chip and the dead-time free high resolution F1-TDC. The 120 ps time resolution of the digital card guarantees negligible background from uncorrelated physical events. In the outer part of the detector, where the particle rates are lower, the present multi-wire proportional chambers (MWPC) with Cesium Iodide photo-cathodes have been upgraded with a new read-out electronic system based on the APV preamplifier and shaper ASIC with analog pipeline and sampling ADCs. The project was fully designed and implemented in the period November 2004 until May 2006. The upgraded detector showed an excellent performance during the 2006 data taking: the number of detected Cherenkov photons per ring was increased from 14 to above 60 at saturation. The time resolution was improved from about 3 microseconds to about one nanosecond which allows an excellent suppression of the background photons from uncorrelated events.

Sampling Pulses for Optimal Timing

When extracting unknown band-limited pulses from sampled data, the Nyquist criterion defines the minimum sampling frequency. With well-defined pulse shapes and a stationary noise environment one can use matched filters to recover time and amplitude, but this is usually not the case with scintillation detectors. If the noise is not stationary other methods must be used. Our study investigates different timing strategies and how the timing precision depends on ADC resolution and sample rate. It also compares the timing precision with data obtained from an analogue setup. Pulses from an LSO crystal with photomultiplier readout are studied experimentally. Our best method gives in this case a 10% improvement in timing compared to a matched filter approach. Some simulation results are also reported

An efficient method for timing synchronization between many digital sampling channels

Future nuclear physics experiments are expected to rely more and more on fast digital sampling and digital signal processing methods, for energy, pulse-shape, and timing measurements. A common issue in these applications is the electronic synchronization between the various channels, i.e. the capability of performing timing coincidences or time-of-flight measurements. In this paper an efficient synchronization method is proposed, based on sampling a periodic reference signal with the same digitizer used for the detector signal. A fast digital signal processing algorithm to extract the relevant information from the data is presented and discussed. Calculations and experimental tests show that timing synchronization resolutions of the order of 10–100ps FWHM are achievable, using standard fast sampling ADCs. The method can be easily applied to experiments having many channels and possibly different ADC sampling rates, thus overcoming one of the major drawbacks of the time-stamped clock approaches.

Photonic analog-to-digital converters

This paper reviews over 30 years of work on photonic analog-to-digital converters. The review is limited to systems in which the input is a radio-frequency (RF) signal in the electronic domain and the output is a digital version of that signal also in the electronic domain, and thus the review excludes photonic systems directed towards digitizing images or optical communication signals. The state of the art in electronic ADCs, basic properties of ADCs and properties of analog optical links, which are found in many photonic ADCs, are reviewed as background information for understanding photonic ADCs. Then four classes of photonic ADCs are reviewed: 1) photonic assisted ADC in which a photonic device is added to an electronic ADC to improve performance, 2) photonic sampling and electronic quantizing ADC, 3) electronic sampling and photonic quantizing ADC, and 4) photonic sampling and quantizing ADC. It is noted, however, that all 4 classes of "photonic ADC" require some electronic sampling and quantization. After reviewing all known photonic ADCs in the four classes, the review concludes with a discussion of the potential for photonic ADCs in the future.

Design and performances of a multichannel high resolution simultaneous sampling ADC card with on-board data elaboration capabilities

The first prototype for the CUORE digitizing board (CDB) has been realized and characterized by the INFN Genova group. The board has a 6U VME format ( 233 × 280 mm ) , 12 independent inputs, buffering capabilities and is fully programmable via VME interface. Each channel has auto-triggering capabilities, is completely independent and the sampling circuit has zero dead time. Each input is equipped with an 18 bit ADC whose sampling speed is programmable up to a maximum of 5 kHz. The measured resolution is 1 LSB r.m.s. A description of the board is provided and its measured performances are shown.

Digital filtering and analysis for a semiconductor X-ray detector data acquisition

Pile-up distortion is a major drawback in X-ray spectroscopy at high count rate. Pulse width narrowing with shaping techniques can lead to the reduction of the pile-up distortion, but a low shaping time reduces the noise filtration and leads to a poor energy resolution. Thus, only a best compromise solution between the pile-up and the noise requirements is achievable. The hardware manipulation needed to adjust the parameters of the traditional electronic shaping amplifiers makes it uneasy to tests various settings in different conditions. Digital techniques can help to overcome such difficulties. A digital signal processing and analysis system for X-ray spectroscopy is described in this paper. The system processes the output signal of a Charge Sensitive Preamplifier (CSPA) connected to an X-ray semiconductor detector. The output CSPA signal is registered with a high speed ADC (sampling rate up to 100 MS/s, 14 bit resolution) and a fully digital shaping is performed off-line by a dedicated software instead of analog electronics. The software carries out the rest of data analysis (peak detection, pile-up recognition, rejection or correction) and finally calculates the photon count, constructs the spectrum and extracts other useful information. We processed the output signals of an Amptek ® XR-100 T CdTe detector used with mammographic X-ray beams. We developed the system with the LabVIEW ® platform. The software is characterized by a user friendly GUI which make it easier to change settings than traditional electronics.

Performance Simulation Studies of the Clear-PEM DAQ/Trigger System

The Clear-PEM detector is a positron emission mammography scanner based on a high-granularity avalanche photodiode readout with 12 288 channels. The front-end sub-system is instrumented with low-noise 192:2 channel amplifier-multiplexer ASICs and free-running sampling ADCs. The off-detector trigger, implemented in a FPGA based architecture, computes the pulses amplitude and timing required for coincidence validation from the front-end data streams. A high-level C++ simulation tool was developed for data acquisition performance analysis and validated at bit-level against FPGA VHDL testbenches. In this work, simulation studies concerning the performance of the on-line/off-line energy and time extraction algorithms and the foreseen detector energy and time resolution are presented. Time calibration and trigger efficiency are also discussed

Jitter measurement circuit for mixed signal production test

This paper presents a novel low-cost jitter measurement circuit for production test. The hardware implementation is based on the so-called analytic signal method. The circuit consists of two parts: high-speed ADC sampling and DSP computation. The uniqueness of this circuit comes from the fact that the FPGA is used as both the ADC sampling controller and the main computation engine, which can significantly reduce the test cost. To validate the design effectiveness, measurements results have been compared between various instruments and this proposed circuit.

Digital-sampling systems in high-resolution and wide dynamic-range energy measurements: Comparison with peak sensing ADCs

The use of fast digital sampling techniques in Nuclear Physics experiments as a replacement of the standard analog signal processing methods is discussed for applications needing high-resolution signal amplitude measurements. This is for example the case of a solid-state detector with a charge-sensitive preamplifier, processed using fast digital sampling methods. Under very general assumptions, an expression for the achievable resolution and dynamic range of the system is reported, valid for any detector/digitizer/digital-filter combination, taking into account the detector noise and the ADC properties, namely the Effective Number of Bits (ENOB) and the sampling frequency. The system properties are summarized using the parameter PSENOB, i.e. the “Peak-Sensing-Equivalent Number of Bits”. These results can be used to predict the attainable performances in various applications, possibly requiring a resolution/dynamic-range trade-off. Numerical examples for some representative cases in γ -ray spectroscopy and charged particle experiments are reported, demonstrating that the equivalent performances of a 15 bit peak-sensing ADC are feasible with today-available sampling ADCs. For ease of presentation, other non-trivial effects as baseline- and non-linearity-related issues as well as experimental tests of the proposed approach are presented in a companion paper [L. Bardelli, G. Poggi, Digital sampling-systems in high-resolution and wide dynamic-range energy measurements: finite time window, baseline effects, and experimental tests, this issue].

PISA – an experiment for fragment spectroscopy at the Internal Beam of COSY: application of an Axial Ionization Chamber

The Proton-Induced SpAllation (PISA) experiment performed at the internal beam facility of the COSY storage ring in Jülich, Germany, which is aimed at the precise measurement of double differential cross-sections over a broad range of energies and angles for spallation reactions induced by protons of 200– 2500 MeV energy in various targets, is presented. In this paper the emphasis is put on the design, principles of operation and performance of a Bragg Curve Detector (BCD) optimized for internal beam experiments at storage rings. Very clean and distinct product identification (with Z up to ∼14) from reactions, in which a Ni target was bombarded with a 1.9 GeV circulating proton beam, is obtained. The individual elements are resolved for emission energies higher than 0.5 MeV/ nucleon . Moreover, due to the detector read-out achieved by coupling a specially designed current sensitive preamplifier directly to a sampling ADC, the shape analysis of the signals from the BCD allows the isotope identification of light particles with A up to ∼11. It is also found that the BCD can be used efficiently as a thin Δ E detector for the telescope consisting of the BCD and a series of silicon detectors.

Multipulse time of flight technique of variable resolution based on linear processing of count pulses

A novel method for measuring the count arrival times, which is effective at higher count rates when more than a single event per scan is detected (multipulse performance), is presented. It is based on the direct ADC sampling of normalized counts and their software processing by deriving a reference count shape from randomly arriving counts, determination of arrival times by comparison with the reference shape, histograming, etc. The dead time by this method does not exceed several times the count pulse duration. The method is also free of dead processing times after the event arrivals in contrast to typical TOF-methods with TACs. A temporal accuracy of order of 10−2 of the ADC sampling step (0.5ns at 20MHz/8bits ADC) has been experimentally demonstrated. This method combines the very high time resolution of the best TOF-techniques (operating at very low count rates) with the higher tolerable count rates of the photon counting techniques (operating at lower resolutions). The unique opportunity for direct computer processing of raw acquired data from the discriminator, realizing variable resolution (zooming) of the retrieved time profiles must be noted.

Performance characteristics of a new generation of processing circuits for PET applications

An electronics architecture for a PET camera is presented which utilizes a newly developed ASIC, CFD, and TDC to fully utilize the timing advantages of an LSO scintillation crystal. Measured intrinsic timing resolution for a LSO/PMT detector against plastic/PMT detector is 900 ps FWHM using the newly developed ASIC electronics. The energy and pixel location are derived using continuous sampling ADCs with FPGA digital processing algorithms. Sampled PMT signals are rescaled using the CFD trigger to recalibrate the energy and position since the ADCs are asynchronous with the events. The overall linearity of the energy channels is 1.8% for a 6:1 input dynamic range. The electronics are designed to be compatible with large and small area LSO or BGO detectors used in PET imaging.

Digital pulse-shape processing for CdTe detectors

CdTe detectors suffer from low photo-peak efficiency and poor energy resolution. These problems are due to the drift properties of charge carriers in CdTe where particularly the holes have small mobility and trapping time. This is reflected in the amplitude and the shape of the detector output. To improve this situation a digital method is introduced where a sampling ADC is used to make a detailed measurement of the time evolution of the pulse. The measured pulse shape is fitted with a model. For the detector under study a model taking hole trapping into account significantly improves the photo-peak efficiency. The description of the hole component is, however, not fully satisfactory since for pulses with a large hole contribution a broadening of the full-energy peak occurs. Allowing for inhomogeneities in the detector material within the model partially remedies this deficiency.

Measuring the arrival times of overlapped photo-events

We have developed and tested experimentally and by computer simulations a novel method for measuring the individual arrival times of temporally non-resolved (overlapped) single-photon detector pulses in high-intensity streams. The method is based on a set of linear transformations of photo-event pulses into a deconvolution, a transformation to standardized functions, a non-linear Chi-square fitting, etc. The retrieving accuracy varies within the range of 2–4 ns at an ADC sampling interval of 50 ns. The simultaneous measurement without dead time effects of the main photon statistics distributions as the distribution of intraevent intervals and the charge distributions has been demonstrated. The method covers the intermediate scale of intensities, where other well-known techniques for processing of photo-events are ineffective. It can be effectively applied in nuclear experiments, time-resolved spectroscopy, optical remote sensing, etc.