Charge Integration Research Articles

Extension to Nonconforming Meshes of the Combined Current and Charge Integral Equation

We bring out some mathematical properties of the current and charge boundary integral equation when it is posed on a surface without geometrical singularities. This enables us to show that it is then possible to solve this equation by a boundary element method that requires no interelement continuity. In particular, this property allows the use of meshes on various parts of the surface obtained independently of each other. The extension to surfaces with geometrical singularities showed that acute dihedral angles can lead to inaccuracies in the results. We built a two-dimensional version of this equation which brought out that the wrong results are due to spurious oscillations concentrating around the singular points of the geometry. Noticing that the system linking the current and the charge is a saddle-point problem, we have tried augmenting the approximation of the charge to stabilize the numerical scheme. We show that this stabilization procedure, when coupled with a refinement of the mesh in the proximity of the geometrical singularities, obtained by a simple subdivision of the triangles, greatly reduces the effect of these instabilities.

Pulse shape discrimination and classification methods for continuous depth of interaction encoding PET detectors

In previous work we demonstrated the potential of positron emission tomography (PET) detectors with depth-of-interaction (DOI) encoding capability based on phosphor-coated crystals. A DOI resolution of 8 mm full-width at half-maximum was obtained for 20 mm long scintillator crystals using a delayed charge integration linear regression method (DCI-LR). Phosphor-coated crystals modify the pulse shape to allow continuous DOI information determination, but the relationship between pulse shape and DOI is complex. We are therefore interested in developing a sensitive and robust method to estimate the DOI. Here, linear discriminant analysis (LDA) was implemented to classify the events based on information extracted from the pulse shape. Pulses were acquired with 2×2×20 mm3 phosphor-coated crystals at five irradiation depths and characterized by their DCI values or Laguerre coefficients. These coefficients were obtained by expanding the pulses on a Laguerre basis set and constituted a unique signature for each pulse. The DOI of individual events was predicted using LDA based on Laguerre coefficients (Laguerre-LDA) or DCI values (DCI-LDA) as discriminant features. Predicted DOIs were compared to true irradiation depths. Laguerre-LDA showed higher sensitivity and accuracy than DCI-LDA and DCI-LR and was also more robust to predict the DOI of pulses with higher statistical noise due to low light levels (interaction depths further from the photodetector face). This indicates that Laguerre-LDA may be more suitable to DOI estimation in smaller crystals where lower collected light levels are expected. This novel approach is promising for calculating DOI using pulse shape discrimination in single-ended readout depth-encoding PET detectors.

Charge integration in external PIXE–PIGE for the analysis of aerosol samples

The beam current in an external-beam PIXE–PIGE is difficult to accurately measure due to ionization along the beam path in the atmosphere. Charge integration was measured using a homemade Faraday cup, and assessed by the peak area of Ar Kα X-rays, which were induced by protons near the sample. The X-ray peak integral from a thin Fe reference sample, which was positioned between the exit window and the Faraday cup, was determined to evaluate the performance of the homemade Faraday cup. Moreover, the effects of different membrane filters and samples with different elements on the beam current measurement of the aforementioned methods were studied by placing different blank films or reference standards behind a reference Mn target. The results indicated that the charge measurement of the homemade Faraday cup was reliable for external PIXE–PIGE analysis of aerosol samples.

A non-linear algorithm for current signal filtering and peak detection in SiPM

Read-out of Silicon Photomultipliers is commonly achieved by means of charge integration, a method particularly susceptible to after-pulsing noise and not efficient for low level light signals. Current signal monitoring, characterized by easier electronic implementation and intrinsically faster than charge integration, is also more suitable for low level light signals and can potentially result in much decreased after-pulsing noise effects. However, its use is to date limited by the need of developing a suitable read-out algorithm for signal analysis and filtering able to achieve current peak detection and measurement with the needed precision and accuracy. In this paper we present an original algorithm, based on a piecewise linear-fitting approach, to filter the noise of the current signal and hence efficiently identifying and measuring current peaks. The proposed algorithm is then compared with the optimal linear filtering algorithm for time-encoded peak detection, based on a moving average routine, and assessed in terms of accuracy, precision, and peak detection efficiency, demonstrating improvements of 1÷2 orders of magnitude in all these quality factors.

SU-E-T-175: A Study on Design and Fabrication of 25 * 25 cm2 Beam Monitor for Scanning Carbon Beam.

The KHIMA is developing a superconducting cyclotron of 430 MeV/u for carbon therapy. In order to verify the irradiated beam dose and position, detectors have been developed. The detector has a considered in the active area of 25*25cm2 to cover the entire beam scanning area. To minimize the loss of data during beam irradiation, a fast data acquisition system was required. A PPIC type was adopted. To measure the beam position and profile, the electrode of PPIC was designed to have a strip pattern. The PCB technique was applied to large area with thin FR-4 plate of electrodes. The chamber has a strip interval of 1.7mm. He was used as the filling gas in order to reduce the ion collection time. Output signal from the detector connected to the two charge integrators was transferred every 10us. The signal can be stored temporarily in memory of FPGA through one of 2 integrators. The fabricated large electrode plates did not show any deformation on their shape. Depending on the beam position, the amount of dose from the ion chamber will be measured. For fast data acquisition, the DAQ board was fabricated by using 2 charge integrators and the FPGA. The obtained data from the ion chamber was displaced on the PC screen every 10us. The fluence map of a single layer will be shown on the PC screen at the end of beam irradiation on the layer. The output data from the profile monitor will be compared with Gafchromic Film results. PCB method for active area of thin electrodes was used in the strip pattern. To reduce the loss of data during irradiation, 2 charge integrators are used alternately. The response of the readout data was set 1 0us. The beam tests will be performed with the MC-50 Cyclotron.

Analyzing the Radiation Degradation of 4-Transistor Deep Submicron Technology CMOS Image Sensors

This paper presents a radiation degradation study on 4-Transistor (4T) complementary metal-oxide-semiconductor (CMOS) image sensors designed in standard 0.18-μm technology. The significant contribution of this paper is a systematic evaluation of the X-ray radiation effects on image sensors from the individual device level, to the pixel level and to the level of the entire sensor. The major degradation parameters of the sensor have been analyzed. This paper also includes test structures of varying geometries of in-pixel MOSFETs, pinned photodiodes (PPD), and transfer gates (TG). Characterization was performed during different X-ray doses up to 109 krad. The major degradation-an increase in the dark signal-is analyzed by modifying the TG charge transfer time and integration time. The PPD and the TG are the elements most sensitive to the dark signal of the sensor. The radiation-related dimensional effects on the sensors are also evaluated, which show different results compared to 3T pixels. The transfer-gate length influences the dark signal due to not only the electric field variation in the TG channel but also the local defect generations. In-pixel MOSFETs are used to identify the origin of increases in radiation-induced dark signal. Shallow trench isolation (STI) oxides are responsible for the radiation degradation of the sensor. A slight degradation of the quantum efficiency was observed after radiation in the short-wavelength region. Basic hardening-by-design techniques are also presented. The discussion results of the radiation-related dimensional effects on the sensors together with the STI effect can be used as a guideline for future layout designs of radiation-tolerant sensors. Identifying the pixel dark current origin can help to determine where and how to suppress the pixel dark current generation more effectively.

Development of wide range charge integration application specified integrated circuit for photo-sensor

A front-end application specified integrated circuit (ASIC) is developed with a wide dynamic range amplifier (WDAMP) to read-out signals from a photo-sensor like a photodiode. The WDAMP ASIC consists of a charge sensitive preamplifier, four wave-shaping circuits with different amplification factors and Wilkinson-type analog-to-digital converter (ADC). To realize a wider range, the integrating capacitor in the preamplifier can be changed from 4pF to 16pF by a two-bit switch. The output of a preamplifier is shared by the four wave-shaping circuits with four gains of 1, 4, 16 and 64 to adapt the input range of ADC. A 0.25-μm CMOS process (of UMC electronics CO., LTD) is used to fabricate the ASIC with four-channels. The dynamic range of four orders of magnitude is achieved with the maximum range over 20pC and the noise performance of 0.46fC + 6.4×10−4fC/pF.

Improved High Efficiency Stacked Microstructured Neutron Detectors Backfilled With Nanoparticle $^{6}$LiF

Silicon diodes with large aspect ratio trenched microstructures, backfilled with <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> LiF, show a dramatic increase in thermal neutron detection efficiency beyond that of conventional thin-film coated planar devices. Described in this work are advancements in the technology using detector stacking methods to increase thermal neutron detection efficiency, along with the current process to backfill <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> LiF into the silicon microstructures. The highest detection efficiency realized thus far is over 42% intrinsic thermal neutron detection efficiency by device-stacking methods. The detectors operate as conformally diffused pn junction diodes each having 1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> area. Two individual devices were mounted back-to-back with counting electronics coupling the detectors together into a single dual-detector device. The solid-state silicon device was operated at 3 V and utilized simple signal amplification and counting electronic components that have been adjusted from previous work for slow charge integration time. The intrinsic detection efficiency for normal-incident 0.0253 eV neutrons was found by calibrating against a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He proportional counter.

A sigma–delta interface ASIC for force-feedback micromachined capacitive accelerometer

A single-loop fourth-order sigma---delta (ΣΔ) interface circuit for micromachined accelerometer is presented in this study. Two additional electronic integrators are cascaded with the micromachine sensing element to form a fourth-order loop filter to eliminate quantization noise. A precise model for the overall system is set up based on nonlinear model of 1-bit quantizer. Three main noise sources affecting the overall system resolution of a ΣΔ accelerometer: mechanical noise, electronic noise and quantization noise are analyzed in more detail. A switched-capacitor charge integrator and correlated double sampling are applied to reduce input-referred electronic noise. The ASIC is fabricated in 0.5 μm two-metal two-poly n-well CMOS process, and test results show that the noise density floors of the open-loop and closed-loop modes are 12 and 80 μg/Hz1/2, respectively, the sensitivity is 1.25 V/g, the full measurement range can be achieved from ?2 to +2 g, and the power dissipation is 40 mW.

R&D in photosensors and data acquisition systems for a new generation of Cosmic Ray Cherenkov and Fluorescence Imaging focal planes

In this work we present the design, first prototypes and experimental R&D activities on the development of novel imaging cameras for Imaging Atmospheric Cherenkov and Fluorescence Telescopes. The baseline solution for the focal plane is based on a photosensor architecture instrumented with Silicon Photomultipliers (SiPMs). To decrease the trigger threshold and improve the signal-to-noise ratio for low-energy events, the Photon Counting technique is used. For very bright events the conventional Charge Integration approach is retained. The large number of channels requires a compact and modular design with minimal cabling and distance between the photosensors and the frontend. Other design requirements are an efficient light concentration system treated with an anti-reflective coating, a liquid cooling system able to keep the SiPMs at a temperature of −20°C to −10°C, a low-power frontend electronics down to 1kW/m2 and an easy field maintenance, high reliability data acquisition and trigger system. In the baseline design, the data acquisition system is partitioned in on-board frontend and off-detector high-level trigger electronics. Extensive use of mixed-signal ASICs and low-power FPGAs for early data reduction (Level 1 trigger), compatible with a liquid cooling sub-system for temperature control is adopted. The off-detector data acquisition and higher trigger (Level 2 and Level 3) architecture is based on the VME64X standard. The boards are connected by multi-Gbps optical links to the focal plane camera. Trigger primitives are sent asynchronously to the trigger boards via data links running at their own clocks. Data and slow-control data streams are also sent over the same links with the parallel VME64X backplane kept for trigger board configuration, slow-control and final data readout. Each 8-slot 6U crate can process up to about 3.6×104 SiPM channels.

Optimizing read-out of the NECTAr front-end electronics

We describe the optimization of the read-out specifications of the NECTAr front-end electronics for the Cherenkov Telescope Array (CTA). The NECTAr project aims at building and testing a demonstrator module of a new front-end electronics design, which takes an advantage of the know-how acquired while building the cameras of the CAT, H.E.S.S.-I and H.E.S.S.-II experiments.The goal of the optimization work is to define the specifications of the digitizing electronics of a CTA camera, in particular integration time window, sampling rate, analog bandwidth using physics simulations. We employed for this work real photomultiplier pulses, sampled at 100ps with a 600MHz bandwidth oscilloscope.The individual pulses are drawn randomly at the times at which the photo-electrons, originating from atmospheric showers, arrive at the focal planes of imaging atmospheric Cherenkov telescopes. The timing information is extracted from the existing CTA simulations on the GRID and organized in a local database, together with all the relevant physical parameters (energy, primary particle type, zenith angle, distance from the shower axis, pixel offset from the optical axis, night-sky background level, etc.), and detector configurations (telescope types, camera/mirror configurations, etc.).While investigating the parameter space, an optimal pixel charge integration time window, which minimizes relative error in the measured charge, has been determined. This will allow to gain in sensitivity and to lower the energy threshold of CTA telescopes. We present results of our optimizations and first measurements obtained using the NECTAr demonstrator module.

Pulse-shape analysis of Cs 2LiYCl 6:Ce scintillator for neutron and gamma-ray discrimination

Cs 2LiYCl 6:Ce (CLYC) is one of the most promising new scintillators for detecting both neutrons and gamma-rays. Its neutron and gamma-ray discrimination capability using pulse-shape analysis has drawn much attention, and there is significant interest in its use in field applications. For such applications, compact and low-power readout electronics capable of exploiting the pulse-shape discrimination (PSD) capabilities of CLYC will be essential. A readout system centered around a PSD-capable application specific integrated circuit (ASIC) that is well-suited for use with CLYC has been characterized, tested, and validated. As part of this study, automated analysis of CLYC data collected with a fast waveform digitizer extracted optimized charge integration windows for PSD. Additionally, several different CLYC samples were studied in order to gain understanding of the dependance of pulse shapes on parameters such as crystal size, 6Li enrichment level, crystal packaging, and choice of PMT. Extremely good PSD performance was obtained from CLYC scintillator and the ASIC-based readout system.

A wide range, low power clock and data recovery scheme for RFID tags

An extremely low power clock and data recovery (CDR) circuit that covers a large input speed range is reported in this paper. The CDR recovers accurately-synchronized clock and data directly from the pulse position modulated (PPM) input, and the bit information embedded in time domain is converted into a voltage through charging integration on linear capacitors. The threshold voltage required for data recovery is accurately generated from the input bit period to produce the best noise margin for both bit 1 and bit 0. Furthermore, the current that is used for charge integration is dynamically set by a feedback loop to expand the input speed range. The prototype CDR circuit was implemented using a standard CMOS 0.25 μm technology. Results show that the designed prototype can cover a large input speed range from 0.5 to 500 kbit/s, while only consumes 11---75 μW of power, respectively.

Electrical and optical spin injection in ferromagnet/semiconductor heterostructures

Spin-based electronics or ‘spintronics’ is a rapidly expanding research area that offers the promise of surpassing the limits of conventional electrical charge-based semiconductor devices with potential advantages in speed and power consumption. For electron spin to be successfully employed in a spintronic device, the integration of electron charge and electron spin in a semiconductor is one of the central issues. In the basic concept of a spintronic device at present, the device functionality relies primarily on three different key processes: spin injection, spin manipulation and spin detection in ferromagnet/semiconductor heterostructures. This article reviews the current status of research on spin injection in semiconductors by both electrical and optical means and discusses the electron spin transport processes across the interface based on optical spin orientation.

Application of Functionalized CNT–Polymer Composite Electrolytes for Enhanced Charge Storage in "All Solid-State Supercapacitors"

The ability of specifically functionalized carbon nanotubes to enhance proton transport in Nafion and polybenzimidazole membranes leading to improvement in the specific capacitance of an all solid-state supercapacitor is demonstrated. Cyclic voltammetry experiments reveal a 25% improvement (185 and 150 F per gram of RuO2 for composite and Nafion membranes respectively) in capacitance by a meager 0.05 wt% addition of sulfonated MWCNTs in Nafion membranes. On the other hand, an addition of 1% phosphonated MWCNTs results in ∼60% improvement in olybenzimidazole (PBI) based composites (from 160 to 260 F g−1). Further, composite membranes based on functionalized MWCNTs show increased cycle life which is attributed to the presence of electrostatically linked network structures due to functional moieties on the side walls of carbon nanotubes that increases the interfacial charge density and integrity of the membrane. The equivalent series resistance for the PBI and PBI phosphonated MWCNT (PBpNT) membranes is 470 and 89 milli ohm respectively suggesting improved proton conductivity with the composite membrane. Charge discharge measurements reveal a capacitance value of 500 F g−1 for PBpNT membrane based supercapacitors even after 1000 cycles of operation. Use of such nanocomposite membranes is expected to dramatically improve the life time as well as performance of supercapacitors which in turn would facilitate deployment in different applications such as hybrid electric vehicles.

A 70μm × 70μm CMOS digital active pixel sensor for digital mammography and X-ray imaging

This work presents an architecture for CMOS active pixel sensors (APS) based on a novel lossless charge integration method, proposed for X-ray imagers in general but specifically optimized for full-field digital mammography. The objective is to provide all the required functionality inside the pixel, so to use full digital control and read-out signals only, therefore avoiding crosstalk between analog lines over large pixel arrays. It includes a novel lossless A/D conversion scheme besides a self-calibrating dark current cancellation circuit, a self-biasing circuitry, biphasic current sensing for the collection of electrons (e-) or holes (h+) and built-in test. Furthermore, FPN compensation is available by individually addressing the pixel's internal DAC controlling the gain. Implemented in a 0.18μm 1P6M CMOS technology with MiM capacitors, everything fits into a 70μm by 70μm due to the extensive reuse of available blocks and aggressive layout techniques. Also, thanks to the MOSFET subthreshold operation, the average power consumption is as low as 8μW/pixel.

Accurate and efficient algorithm for Bader charge integration

We propose an efficient, accurate method to integrate the basins of attraction of a smooth function defined on a general discrete grid and apply it to the Bader charge partitioning for the electron charge density. Starting with the evolution of trajectories in space following the gradient of charge density, we derive an expression for the fraction of space neighboring each grid point that flows to its neighbors. This serves as the basis to compute the fraction of each grid volume that belongs to a basin (Bader volume) and as a weight for the discrete integration of functions over the Bader volume. Compared with other grid-based algorithms, our approach is robust, more computationally efficient with linear computational effort, accurate, and has quadratic convergence. Moreover, it is straightforward to extend to nonuniform grids, such as from a mesh-refinement approach, and can be used to both identify basins of attraction of fixed points and integrate functions over the basins.

TRIM: An architecture for transparent IMS-based mobility

In recent years, the development and deployment of new wired and wireless access network technologies have made the ubiquitous Internet a reality. Users can access anywhere and anytime to the broad set of value-added Internet services, which are delivered by means of the IP protocol. In this context, 3GPP is currently developing the IP Multimedia Subsystem (IMS), as a key element that allows to evolve from the ubiquitous access to the Internet services towards a next generation network model, by providing a set of essential facilities such as session control, QoS, charging and service integration. Nevertheless, several open issues still need consideration before the future Internet becomes real, such as supporting user mobility in IP networks. Although mobility support in the Internet is receiving much attention, IMS networks present inherent particularities that require further analysis. The solutions proposed so far for IMS do not support mobility transparently to the end-user applications, or address the problem by introducing complex changes to the IMS infrastructure. This paper presents TRIM, an architecture for transparent IMS-based mobility. TRIM supports mobility in IMS networks transparently to the end-user applications, which are unaware of the handover management procedures executed between the mobile node and the network. We have performed several experiments with a TRIM prototype, using a real IMS testbed with 3G and WLAN access networks, validating the proposal for UDP and TCP based applications.

Multi-channel integrated circuits for the detection and measurement of ionizing radiation

Abstract The Integrated Circuits (IC) Design Research Laboratory at Southern Illinois University Edwardsville (SIUE) has collaborated with the Nuclear Reactions Group at Washington University (WU) to develop a family of multi-channel integrated circuits. To date, the collaboration has successfully produced two micro-chips. The first was an analog shaped and peak sensing chip with on-board constant-fraction discriminators and sparsified readout. This chip is known as Heavy-Ion Nuclear Physics–16 Channel (HINP16C). The second chip, christened PSD8C, was designed to logically complement (in terms of detector types) the HINP16C chip. Pulse Shape Discrimination–8 Channel (PSD8C), featuring three settable charge integration windows per channel, performs pulse shape discrimination (PSD). This paper summarizes the design, capabilities, and features of the HINP16C and PSD8C ICs. It proceeds to discuss the modifications, made to the ICs and their associated systems, which have attempted to improve ease of use, increase performance, and extend capabilities. The paper concludes with a brief discussion of what may be the next chip (employing a multi-sampling scheme) to be added to our CMOS ASIC “tool box” for radiation detection instrumentation.

Compensation Technique for Capacitive Crosstalk in Continuous-Time Electro-Mechanical Sigma-Delta Modulators

This paper presents a readout interface for gyroscopes, where the Coriolis rate signal is converted into a bitstream using a 4th-order continuous-time electro-mechanical sigma-delta modulator. The used gyroscope has separate sense and feedback electrodes allowing full continuous-time readout. A severe drawback arises when a gyroscope with this non-collocated design is employed, since the readout is active during force-feedback. Charge feed-through, caused by parasitic capacitances of the sensor in combination with force-feedback signals, drive the charge integrator front-end into saturation. This paper presents a technique for the compensation of this capacitive crosstalk, enabling stable closed-loop readout interfaces.