Charge Integration Research Articles

Representation of holomorphic functions of many variables by Cauchy-Stieltjes-type integrals

We consider functions of many complex variables that are holomorphic in a polydisk or in the upper half-plane. We give necessary and sufficient conditions under which a holomorphic function is a Cauchy-Stieltjes-type integral of a complex charge. We present several applications of this criterion to integral representations of certain classes of holomorphic functions.

Stochastic Computing Chip for Measurement of Manhattan Distance

We have proposed a stochastic computing system utilizing arbitrary chaos generators as random signal generators. The system can execute linear and nonlinear computations using the representation of analog quantities by pulse densities with random signals. In the case that a very high accuracy of computation is not required, the stochastic computing system can be implemented efficiently using future scaled complementary metal oxide semiconductor (CMOS) devices and has the programmability of computation time and accuracy without changing hardware. We designed a 0.35 µm CMOS stochastic computing chip for the parallel measurement of Manhattan distance using tent chaos generators, exclusive OR (EXOR) circuits, and two types of summation circuit with analog charge integration and digital pulse counting. By an experiment using a fabricated test chip, we confirmed the operation and accuracy of the stochastic computing chip.

Photon-number-resolving detection at a telecommunications wavelength with a charge-integration photon detector

We demonstrate multiphoton discrimination at a telecommunications wavelength with the readout frequency of 40 Hz by a charge-integration photon detector (CIPD). The CIPD consists of an InGaAs pin photodiode and a GaAs junction field effect transistor as a preamplifier in a charge-integration circuit, which is cooled to 4.2 K to reduce thermal noise. The quantum efficiency of the CIPD (the detector itself) is 80% for 1530 nm light, and the readout noise is measured as 0.26 electrons at 40 Hz. We can construct Poisson distributions of photocarrier numbers with distinct peaks at each photocarrier number, corresponding to a signal-to-noise ratio of about 3.

Current and Charge Integral Equation Formulation

A new stable frequency domain surface integral equation formulation is proposed for the three dimensional electromagnetic scattering of composite metallic and dielectric objects. The developed formulation does not suffer from the low frequency breakdown and leads to a well balanced and stable system on a wide frequency band. Surface charge densities are used as unknowns in addition to the traditional surface current densities. The balance of the system is achieved by using normalized field quantities and by enforcing the continuity of the fields across the boundaries with carefully chosen scaling factors. The linear dependence between the currents and charges is taken into account with an integral operator, and the linear dependence in charges is removed with the deflation method. A combined field integral equation form of the formulation is proposed to remove the internal resonance problem associated to the closed metallic objects. Due to the good balance in the new formulation, fast converging iterative solutions on a very wide frequency band can be obtained. The new formulation and its convergence is verified with numerical examples.

Development and study of anodic Ti/TiO 2 electrodes and their potential use as impedimetric immunosensors

Titanium dioxide films were anodically formed at various potentials up to 65 V in 1 M H 2SO 4. Oxide films were characterized by performing various techniques, including electrochemical impedance spectroscopy, scanning electron microscopy, Raman spectroscopy, ellipsometry and diffuse reflectance FT-IR spectroscopy. Low voltage anodization (up to 10 V) results to amorphous TiO 2, whereas at higher applied potentials (up to 65 V), anatase is the predominant form. Anatase films were further hydroxylated with an acidic agent and the effect of this treatment on the overall impedance of the electrodes was studied with impedance spectroscopy. The potential use of anodic (anatase) Ti/TiO 2 electrodes in the development of impedimetric immunosensors is also demonstrated by monitoring the immunoreaction of avidin/anti-avidin with different instrumental approaches based on a FRA analyzer, an LCR-meter and a home-built charge integrator (Multipulser).

Simple and accurate spectra normalization in ion beam analysis using a transmission mesh-based charge integration

Accurate and reproducible determination of the number of impact ions is essential for quantitative IBA measurements. Herewith we present an in-beam charge-collection device, consisting of a tungsten mesh enclosed by two negatively biased annular electrodes and a shaping slit. The charge-collection efficiency was measured as a function of aperture bias and the reproducibility of charge collection at different bias voltages studied. Scanning transmission ion microscopy (STIM) was used to check the effect of beam scattering at the mesh on its energy distribution. The effect of the device on the primary beam energy distribution was calculated for the beams typically used in Rutherford backscattering spectroscopy (RBS) and elastic recoil detection analysis (ERDA). Excellent characteristics of the device were demonstrated.

Multiple integration method for a high signal-to-noise ratio readout integrated circuit

A multiple integration method is reported that greatly improves the signal-to-noise ratio (SNR) for applications with a high-resolution infrared (IR) focal plane array. The signal from each pixel is repeatedly sampled into an integration capacitor and then output and summed into an outside memory that continues for n read cycles during each period of a frame. This method increases the effective capacity of the charge integration and improves sensitivity. Because a low-noise function block and high-speed operation of the readout circuit is required, a new concept is proposed that enables the readout circuit to perform digitization by a voltage skimming method. The readout circuit was fabricated using a 0.6-/spl mu/m CMOS process for a 64/spl times/64 midwavelength IR HgCdTe detector array. The readout circuit effectively increases the charge storage capacity to 2.4/spl times/10/sup 8/ electrons and then provides a greatly improved SNR by a factor of approximately 3.

Geometric and dosimetric verification of step‐and‐shoot modulated fields with a new fast and high resolution beam imaging system

A technique for geometric and dosimetric pretreatment verification of step‐and‐shoot intensity modulated radiotherapy treatments (IMRT) using a beam imaging system (BIS) made up of a charge‐coupled device (CCD) digital camera optically coupled with a metal‐plate/phosphor screen is described. Some physical properties of BIS were investigated in order to demonstrate its capability to perform measurements with a high spatial resolution and a high sampling rate. High‐speed imaging, with a minimum charge integration time on the CCD of 120 ms, can be performed. The study of the signal‐to‐noise ratio as a function of sampling time is presented. In‐plane and cross‐line pixel size was measured to be , which agrees within 0.5% of the manufacturer value of 0.366 mm. Spatial linearity results are very good and there are no detectable image distortions on whole detector area. A software routine was written to automatically extract positions of the collimator leaves from the images of the field shaped by the multileaf collimator (MLC) and also to compare them with the coordinates from the treatment planning system (TPS), thus directly testing both the MLC positioning and the treatment parameters transfer from TPS to the linear accelerator in a fast and precise way. The dosimetric capabilities (characteristics) of the imaging device for photon beams with energies of 6 and 15 MV were studied. Additional plexiglass buildup layers, depending on x‐ray energy, were needed to reach maximum efficiency. The energy dependence of the BIS response versus dose and dose rate was found to be linear over a wide range. Relative output factors of BIS as a function of field size, compared with values measured with an ionization chamber, were in good accord for smaller field sizes but showed differences up to 4% for all the energies at the respective buildup depth for bigger fields. Square field profiles at water‐equivalent buildup depths, extracted from BIS maps, are compared with the corresponding scans performed with a diode detector. Disagreement is always shown in the regions outside the field penumbra (tails) and near the field edges only for field sizes due to the metal/phosphor screen higher sensitivity to low energy scattering x‐rays. A straightforward correction method for the “tails effect” was developed and then generalized to MLC‐shaped fields. In order to demonstrate the validity of this procedure, the comparison between the two‐dimensional (2D) dose distributions of a triangle MLC‐shaped field and of two simple IMRT fields created by the superimposition of five segments resulting from BIS images and the dose distribution of the same fields achieved by film, was measured and reported. The gamma index method, introduced by Low et al. (1998), was used for 2D dose distributions analysis. Agreements are good for both 6 and 15 MV energies. The described technique provides a lower time‐expensive mean to verify geometric and dosimetric accuracy of the treatment delivered in IMRT with the use of a high resolution beam imaging system and homemade software tools.

SU‐FF‐I‐26: Performance Characterization of a New 41cm by 41cm A‐Si Flat Panel X‐Ray Detector

Purpose: To quantify and report the performance of an a‐Si flat panel X‐ray detector with a new generation electronics design in terms of electronic noise, dynamic range and linearity, as well as to quantify the imaging performance such as MTF and DQE. Method and Materials: The new detector was designed to provide low noise, wide dynamic range and programmable gain for a wide signal range. The signal readout chip has 128 channels, and each consists of a charge integration amplifier, followed by a correlated double sampling stage and a 128:1 multiplexer. The output voltage from the multiplexer is digitized by a 16‐bit analog‐to‐digital converter. The programmable gain can provide settings ranging from the most sensitive of ∼250 electrons per counts (e‐/c) to the least sensitive ∼4,000 (e‐/c). The detector uses a 41cm by 41cm a‐Si flat panel with 200μm pixel pitch and was coated with CsI(Tl). The MTF and DQE measurements were carried out in accordance with the IEC standard. Results: The total detector electronic noise is ∼3200 electrons (500 e‐/c), dynamic range was 78.3dB and the non‐linearity is +/−1.5% over 10–90% of full signal scale range. The MTF and DQE were measured both with and without the protective front cover. Conclusion: The detector with the new readout electronics has met all the major design goals and has raised detector performance to a higher level.

Monitoring of the avidin–biotylinated dextran interaction on Au- and Ti/TiO 2-electrode surfaces using a charge integrating device

In the present paper we report the use of a homemade electronic device (Multipulser), for monitoring interactions between biomolecules that may change the capacitance of an electrode. Multipulser can be used as a stand-alone, low-cost, yet effective alternative monitoring device instead of other well established commercial instruments. The operation of Multipulser is based on the integration of the electric charge used for the repetitive charging of the electrochemical cell capacitance after the application of a predetermined number of short-duration, low-amplitude voltage pulses (perturbation pulses). Multipulser was used to monitor the binding of biotinylated dextran on two different avidin modified electrode assemblies; one based on a thiol SAMs on gold and another based on Ti/TiO 2 semiconductor. Measurements conducted in parallel with a commercial frequency response analyzer gave similar reaction patterns. Pulse polarity dependent behavior was revealed in the case of the Ti/TiO 2-electrode assembly when bipolar potential perturbation modes were used with Multipulser.

Multiphoton discrimination at telecom wavelength with charge integration photon detector

We present a charge integration photon detector (CIPD) that enables the efficient measurement of photon number states at the telecom-fiber wavelengths with a quantum efficiency of 80% and a resolution less than 0.5 electrons at 1Hz sampling. The CIPD consists of an InGaAs pin photodiode and a GaAs JFET in a charge integration amplifier, which is cooled to 4.2K to reduce thermal noise and leakage current. The charge integration amplifier exhibits a low noise level of 470nV∕Hz1∕2. The dark count is as low as 500electrons∕h.

Supramolecular multilayer structures of wired redox enzyme electrodes

Supramolecular multilayer structures comprised of glucose oxidase (GOx), and Os complex derivatised poly(allylamine) (PAH-Os) have been built by alternate layer-by-layer (LBL) electrostatic adsorption in a self-assembly process. The resulting modified electrodes with integrated mediator were tested as reagentless glucose biosensors. The enzyme kinetic parameters and the surface concentration of "wired" enzyme GammaE have been obtained by analysis of the catalytic current dependence on glucose concentrations for the ping-pong mechanism of glucose oxidation. An average osmium volume concentration was estimated by integration of the redox charge in the absence of glucose and the ellipsometric thickness. The total enzyme surface concentration was measured with a quartz crystal microbalance (QCM) during each adsoption step and the fraction of "wired" enzyme and the bimolecular rate constant for FADH2 oxidation by the redox polymer for the different multilayers. The catalytic current increases with the number of LBL layers because the increase in the enzyme loading while the efficiency of enzyme FADH2 oxidation by the Os redox polymer, except for the first dipping cycle remains almost constant at about 2 x 10(4) M(-1) S(-1).

The design of a charge-integrating modified floating-point ADC chip

One of the challenges posed by calorimeters in high-energy physics experiments is digitizing wide dynamic range charge signals at high rate to a specified precision. One response to this challenge is the development of the QIE (charge integrator and encoder) concept. A QIE chip divides the input signal into multiple ranges, with each range integrating a scaled fraction of the signal. The range integrators are offset so that for any given signal magnitude, only one range will be selected as valid. The selected range integrator output is digitized to form a mantissa, and a digital code associated with that range forms an exponent. The resulting modified floating-point output format gives approximately constant measurement precision over a wide dynamic range. Floating-point converter designs are usually tailored for a specific application. A general description of the QIE concept shows how parameters are chosen to suit the application. The design of a mixed-signal chip that has been produced for a specific experiment is presented.

A CdTe real time X-ray imaging sensor and system

A real time X-ray imaging sensor consisting of p-type CdTe pixel detectors with barrier type In front contacts (anode) and Pt pixel contacts (cathode) has been developed and tested. The 5×5 cm 2 sensor area is covered with four CdTe pixel detectors each bump bonded to two CMOS readout circuits and mounted side by side to a support board. Each CMOS has 127×253 pixels with a pitch of 100 μm. The sensor is operated in the charge integration mode. User selective digital video frame output rates up to 60 fps are possible. A detector bias voltage cycle which brings the voltage instantaneously to zero at a certain interval is applied to eliminate the effect of polarization. Real time image calibration is applied to compensate for leakage current variation and CMOS mismatch. The CdTe pixelization process and the sensor design and operation are described. Experimental results of the MTF, SNR and DQE are presented and X-ray images of printed circuit boards are shown.

A low-noise low-offset capacitive sensing amplifier for a 50-/spl mu/g//spl radic/Hz monolithic CMOS MEMS accelerometer

This paper describes a CMOS capacitive sensing amplifier for a monolithic MEMS accelerometer fabricated by post-CMOS surface micromachining. This chopper stabilized amplifier employs capacitance matching with optimal transistor sizing to minimize sensor noise floor. Offsets due to sensor and circuit are reduced by ac offset calibration and dc offset cancellation based on a differential difference amplifier (DDA). Low-duty-cycle periodic reset is used to establish robust dc bias at the sensing electrodes with low noise. This work shows that continuous-time voltage sensing can achieve lower noise than switched-capacitor charge integration for sensing ultra-small capacitance changes. A prototype accelerometer integrated with this circuit achieves 50-/spl mu/g//spl radic/Hz acceleration noise floor and 0.02-aF//spl radic/Hz capacitance noise floor while chopped at 1 MHz.

Highly sensitive measurement of α-rays in NaI(Tl) scintillator by pulse shape discrimination with charge-sensitive analog-to-digital converter

In order to investigate the contamination due to the radioactive isotopes (RIs) in NaI(Tl) scintillator for dark matter search, a simple method of pulse shape discrimination (PSD) to extract α-rays energy spectrum was developed. Two linear signals of different timings were input into a single module charge-sensitive analog-to-digital converter. The α- and the γ-rays were discriminated by comparing the total charge integration of a pulse with the partial one. As a result, the α-rays energy spectrum with NaI(Tl) was successfully and clearly extracted. The present work showed that the PSD method was performed by the minimum electronic circuits. The sensitivity was high enough to measure RIs of a few μBq/kg in high pure NaI crystals for dark matter search.

Piezoelectric response of thin films determined by charge integration technique: Substrate bending effects

Unexpectedly high-longitudinal piezoelectric coefficients have recently been reported in c-axis oriented Pb(Zr,Ti)O3 thin films with morphotropic phase boundary composition [Fu et al., Appl. Phys. Lett. 80, 3572 (2002)]. Our analysis and experimental results show that, in comparison with other methods commonly used to investigate piezoelectric response of thin films, the charge integration technique used by Fu et al. may lead to an order of magnitude higher apparent piezoelectric coefficients if the substrate on which the film was deposited is bent. When this is the case, the large response is due to the transverse piezoelectric effect caused by the substrate bending.

Czech Republic & Germany: Constab — plastics masterbatch

In this paper, we present the design and characteristics of a novel low-noise front-end readout application-specific integrated circuit dedicated to CdZnTe (CZT) detectors for a small animal PET imaging system. A low-noise readout method based on the charge integration and the delayed peak detection is proposed. An eight-channel front-end readout prototype chip is designed and implemented in a 0.35 μm CMOS process. The die size is 2.3 mm ×2.3 mm. The prototype chip is tested in different methods including electronic test, energy spectrum test and irradiation test. The input range of the ASIC is from 2000e− to 180,000e−, reflecting the energy of the gamma ray from 11.2 keV to 1 MeV. The gain of the readout channel is 65 mV/fC at the shaping time of 1 μs. The best test result of the equivalent noise charge (ENC) is 58.9 e− at zero farad plus 5.4 e− per picofarad. The nonlinearity and the crosstalk are less than 3% and less than 2%, respectively, at the room temperature. The static power dissipation is about 3 mW/channel.

Capsule endoscope NORIKA system

The NORIKA Project Team is the development group responsible for the battery-free micro capsule endoscope. RF SYSTEM lab's specialization is the integration of microwave and charge coupled device (CCD) camera technologies. The NORIKA system is powered wirelessly from outside the body, and totally eliminates the risks involved with toxic substances coming from batteries entering the human body. This system can work on continuous stable power supply and guarantee longer durational usage than is possible with batteries. Concerning image reproduction and brightness, the CCD sensor is a primary choice as an image-capturing device, but its power consumption is quite high. To circumvent this, the digital signal processor (DSP), which consumes most of the total power, is separated from the CCD sensor and is placed outside the human body. The camera's focusing feature and the intensity of independently controlled four LED lamps enables clear images to be monitored even in the darkness inside the body. Capsule rotation can also be accomplished for detailed examination. This rotation mechanism combines 3-pole motor theory with strobe light technology. The external unit to transmit data and power includes a coil-embedded vest and a joystick-type controller. The NORIKA system could be an optional diagnostic tool in the near future.

Generalised Sagdeev Potentials for Dusty Plasmas with Varying Grain Charges

Grain charges in a dusty plasma are determined by the random currents from the ambient plasma and vary with the local conditions. The charge on a slowly moving grain will be close to the locally determined equilibrium, given for zero net current to the grain. For a steady electrostatic structure (e.g., solitary wave, double layer) integrals of motion for grains with varying charge can then be found. (These integrals reduce to the total energy if the charge is constant, but in general the electrostatic term becomes an integral of the grain charge with respect to the potential.) Steady state solutions of Vlasov’s equation are piecewise given by arbitrary functions of these integrals of motion. A generalised Sagdeev (Classical) potential can be found, which is, to within an added constant, equal to minus the sum of the total particle pressures (including that of the grains). This extends the well known equivalence found for conventional plasmas and dusty plasmas with constant grain charges. The analysis of dust acoustic solitary waves is modified by additional terms proportional to potential derivatives of the charge. A grain size distribution may be incorporated. The second derivative of the Sagdeev potential (leading to the generalised Bohm condition) is then given in terms of the same effective distribution function as found for linear electrostatic modes. Comparisons are made with several analyses of nonlinear electrostatic structures including dynamical charging.