Current Readout Research Articles

A high precision CMOS weak current readout circuit

This paper presents a high precision CMOS weak current readout circuit. This circuit is capable of converting a weak current into a frequency signal for amperometric measurements with high precision and further delivering a 10-bit digital output. A fast stabilization-enhanced potentiostat has been proposed in the design, which is used to maintain a constant bias potential for amperometric biochemical sensors. A technique based on source voltage shifting that reduces the leakage current of the MOS transistor to the reverse diode leakage level at room temperature was employed in the circuit. The chip was fabricated in the 0.35 μm chartered CMOS process, with a single 3.3 V power supply. The interface circuit maintains a dynamic range of more than 100 dB. Currents from 1 pA to 300 nA can be detected with a maximum nonlinearity of 0.3% over the full scale.

Fast DEPFET current readout for X-ray astronomy missions

The DEPFET-based Active Pixel Sensor (APS) matrix is a new detector concept for X-ray imaging and spectroscopy applications. This type of detector can provide excellent energy resolution and high-speed readout. Both of these features, along with the advantage of random pixel accessibility, can fulfill the requirements of new imaging applications in the X-ray band. In a matrix arrangement, each pixel must be read out by a time-variant filter, so a proper multi-channel integrated filtering amplifier is needed. To operate large area matrices at very fast processing times, we have recently proposed a current readout configuration. In this paper, we explore the performance offered by this circuit when operated with a DEPFET matrix, specifically concerning its ultimate speed capabilities and the trade-off achieved between electronics noise and processing time.

Simultaneous Alternating and Direct Current Readout of Protein Ion Channel Blocking Events Using Glass Nanopore Membranes

Alternating current (ac) phase-sensitive detection is used to measure the conductance of the ion channel alpha-hemolysin (alphaHL), while simultaneously applying a direct current (dc) bias to electrostatically control the binding affinity and kinetics of charged molecules within the protein lumen. Ion channel conductance was recorded while applying a 10-20 mV rms, 1-2 kHz bias across a single alphaHL protein inserted in a 1,2-diphytanoyl-sn-glycero-3-phosphocholine lipid bilayer that is suspended across the orifice (100-500 nm radius) of a glass nanopore membrane. Step changes in the ac ion channel conductance with a temporal response (t(10-90)) of 1.5 ms and noise amplitude of approximately 2 pA were obtained using a low-noise potentiostat and a lock-in amplifier. These conditions were used to monitor the reversible and stochastic binding of heptakis-(6-O-sulfo)-beta-cyclodextrin and a nine base pair DNA hairpin molecule to the ion channel. Alternating current methodology allows the binding kinetics and affinity between the protein ion channel and analyte to be investigated as a function of the dc bias, including ion channel conductance measurements in the absence of a dc bias.

Radio-frequency scanning tunnelling microscopy

The scanning tunnelling microscope (STM) relies on localized electron tunnelling between a sharp probe tip and a conducting sample to attain atomic-scale spatial resolution. In the 25-year period since its invention, the STM has helped uncover a wealth of phenomena in diverse physical systems--ranging from semiconductors to superconductors to atomic and molecular nanosystems. A severe limitation in scanning tunnelling microscopy is the low temporal resolution, originating from the diminished high-frequency response of the tunnel current readout circuitry. Here we overcome this limitation by measuring the reflection from a resonant inductor-capacitor circuit in which the tunnel junction is embedded, and demonstrate electronic bandwidths as high as 10 MHz. This approximately 100-fold bandwidth improvement on the state of the art translates into fast surface topography as well as delicate measurements in mesoscopic electronics and mechanics. Broadband noise measurements across the tunnel junction using this radio-frequency STM have allowed us to perform thermometry at the nanometre scale. Furthermore, we have detected high-frequency mechanical motion with a sensitivity approaching approximately 15 fm Hz(-1/2). This sensitivity is on par with the highest available from nanoscale optical and electrical displacement detection techniques, and the radio-frequency STM is expected to be capable of quantum-limited position measurements.

VELA: The CMOS Circuit Based on Fast Current Read-Out for X-Ray Spectroscopy With DePMOS

DePMOS based active pixel sensor (APS) matrix is a new detector concept for X-ray imaging and spectroscopy applications. This type of X-ray detector can provide excellent energy resolution and high-speed readout. Both these features and the advantage of random pixel accessibility can fulfill the requirements of new space applications, like the XEUS wide field imager. In a matrix arrangement, each pixel must be read out by a time variant filter, so a new readout mechanism and a proper multi-channel integrated shaping amplifier are needed. To operate at the required fast processing time (e.g., 4 per line) DePMOS transistor cannot be operated in the classical source follower configuration, because this results in a long settling time. So a new design for multi-channel readout of the DePMOS matrix has to be considered. We propose a new fast readout concept, which is based on the DePMOS drain current readout and processing.

A composite ISFET readout circuit employing current feedback

This paper presents the concept of a current mode readout circuit for the ion-sensitive field effect transistor (ISFET) to be used as a pH sensor. An ISFET in conjunction with a current mirror with global feedback to the source terminal yields linearity between a wide dynamic pH range and output. Operating the ISFET and current source in the weak inversion region reduces major problems arising from channel-length modulation. Our experiment using discrete components demonstrates very high accuracy readout with total power consumption including the ISFET of early microwatts.

Current Mode Monolithic Active Pixel Sensor With Correlated Double Sampling forCharged Particle Detection

A monolithic active pixel sensor operating in current mode for charged particle detection is described. The sensing element in each pixel is an n-well/p-sub diode with a PMOS transistor integrated in an n-well. The drop of the n-well potential from the collection of charge modulates the transistor channel current. Each pixel features two current mode memory cells. The subtraction of distant-in-time samples frees the signal of fixed pattern noise (FPN) and of the correlated low-frequency temporal noise components, resulting in extraction of the particle footprint. The subtraction circuits are placed at each column end. A transimpedance amplifier, integrating in sequence two current samples and subtracting the results in an arithmetic operation, was adopted. The integrated version of the transimpedance amplifier, designed with a maximized conversion gain, is burdened by a risk of an early saturation, imperiling its operation, if the dispersions of the dc current component are too big. The degree of dispersions could not be estimated during the design. Some number of columns is available as a backup with the direct current readout. An external realization of the subtracting circuit, based on the same principle, is used to process direct output columns. The concept of the data acquisition setup developed, the tested performance of an array of cells, and the processing circuitry are described

横型オーバフロー蓄積と電流読出し動作を組合せたダイナミックレンジ２００ｄＢ超のＣＭＯＳイメージセンサ

A wide dynamic range 64x64 CMOS image sensor with 20x20um 2 pixel that combines a lateral-overflow integration voltage-readout operation with the current readout operation from the buried photo-diode hasbeen developed.In the voltage readout operation,an over 160-dB dynamic range image with a linear response isobtained from sequential electronic shutter operations from 1/30 s to 1/130 ks with a dynamic range of about 100-dB within a light intensity range from about 10 -2lx to 106lx.In addition,an over 200-dB dynamic range perform-ance of up to 108lx or more with few time exposures in the high illuminance region is made possible by combiningit with the current reading operation.More than 40 dB for all noises,including photon shot noise,occurs around all the switching points.

Integrating Silicon detector with segmentation for scanning transmission X-ray microscopy

Scanning transmission X-ray microscopes require detectors with high quantum efficiency and wide dynamic range. While large area detectors provide absorption contrast, the addition of spatial segmentation adds phase contrast imaging capabilities. We describe a charge integrating Silicon detector for use at energies from 200–1000 eV. The detector uses patterned rectifying junctions on high-resistivity n-type Silicon, with separate current readout for each segment. The detector has been subdivided into eight regions arranged in a circular geometry according to the beam profile in a scanning X-ray microscope. The uncooled chip is fully depleted by a positive bias voltage applied at the ohmic contact on the back side. X-rays are collected on the radiation-hard back side with very high efficiency ( > 75 % for 250 eV X-rays), and compact, low-noise electronics integrate the current from the detector segments. The RMS noise of the combined system is about 500 electrons/channel for a 1 ms integration time, which is equivalent to about five photons per channel at 360 eV X-ray energy.

Digital readouts for large microwave low-temperature detector arrays

Over the last several years many different types of low-temperature detectors (LTDs) have been developed that use a microwave resonant circuit as part of their readout. These devices include microwave kinetic inductance detectors (MKID), microwave SQUID readouts for transition edge sensors (TES), and NIS bolometers. Current readout techniques for these devices use analog frequency synthesizers and IQ mixers. While these components are available as microwave integrated circuits, one set is required for each resonator. We are exploring a new readout technique for this class of detectors based on a commercial-off-the-shelf technology called software defined radio (SDR). In this method a fast digital to analog (D/A) converter creates as many tones as desired in the available bandwidth. Our prototype system employs a 100 MS/s 16-bit D/A to generate an arbitrary number of tones in 50 MHz of bandwidth. This signal is then mixed up to the desired detector resonant frequency ( ∼ 10 GHz ) , sent through the detector, then mixed back down to baseband. The baseband signal is then digitized with a series of fast analog to digital converters (80 MS/s, 14-bit). Next, a numerical mixer in a dedicated integrated circuit or FPGA mixes the resonant frequency of a specified detector to 0 Hz, and sends the complex detector output over a computer bus for processing and storage. In this paper we will report on our results in using a prototype system to readout a MKID array, including system noise performance, X-ray pulse response, and cross-talk measurements. We will also discuss how this technique can be scaled to read out many thousands of detectors.

Modular pipeline readout electronics for the SuperBelle drift chamber

In order to explore new physics in B-meson decays we plan to upgrade the KEK B-factory to a luminosity of 5/spl times/10/sup 35/ cm/sup -2/ s/sup -1/. In parallel we are developing a new pipelined data acquisition system for the Belle detector to cope with higher trigger rates of up to 30 kHz and severe background conditions. In order to reduce development and maintenance costs, we have adopted a modular design for these new readout electronics. The chosen architecture consists of a common readout platform, upon which are mounted subdetector specific parts, customized to meet the readout requirements of each sub detector component. As an example of this new architecture, we present in this paper the design of drift chamber electronics. The drift chamber readout utilizes the AMT-3 time-to-digital converter chip, originally developed for the ATLAS experiment, which satisfies the performance requirement for current and future Belle drift chamber readout. A data transfer performance test with emulation modules, mounted on the common platform, shows that the new readout electronics works well at a more than 30 kHz input trigger rate.

New dark current suppression CMOS readout circuit with novel CDS structure for large format QWIP FPA

A new Dark Current Suppression (DCS) CMOS readout circuits for large format Quantum-Well-Infrared Photo-detector (QWIP) Focal-Plane-Array (FPA) with novel Correlated-Double-Sampling (CDS) structure based on dynamic source-follower are proposed, which can overcome the drawbacks of the present techniques, such as sensitive to the non-uniformity of the QWIP materials, poor readout noise features, low frame frequency, limited injection efficiency and dynamic range, etc. The dummy is adopted to realize dark current suppression, while the cascode current mirror (with current ratio of 1:10) can increase charge sensitivity and reduce integration time. Through the novel CDS structure, the output waveform is boxcar, and the frame frequency is increased. Simulation results demonstrate that, in high background sense, the proposed DCS circuit can suppress the dark current, achieve good readout performance, such as low power consumption, high charge sensitivity, high resolution, large dynamic range, and insensitive to the non-uniformity of the QWIP materials.

A measurement of parity-violating gamma-ray asymmetries in polarized cold neutron capture on [formula omitted], [formula omitted], and [formula omitted

An apparatus for measuring parity-violating asymmetries in gamma-ray emission following polarized cold neutron capture was constructed as a 1/10th scale test of the design for the forthcoming n → + p→ d+ γ experiment at LANSCE. The elements of the polarized neutron beam, including a polarized 3 He neutron spin filter and a radio frequency neutron spin rotator, are described. Using CsI(Tl) detectors and photodiode current mode readout, measurements were made of asymmetries in gamma-ray emission following neutron capture on 35 Cl , 113 Cd , and 139 La targets. Upper limits on the parity-allowed asymmetry s n·( k γ× k n) were set at the level of 7×10 −6 for all three targets. Parity-violating asymmetries s n· k γ were observed in 35 Cl , A γ=(−29.1±6.7)×10 −6, and 139 La , A γ=(−15.5±7.1)×10 −6, values consistent with previous measurements.

Microchannel plate image readouts:: in search of high resolution and count rate

The search for the ultimate imaging performance in microchannel plate (MCP) detector systems invariably ends in compromise between competing factors in both the operational and performance arenas. We discuss these compromises in the context of the trade-offs made by current state-of-the-art readout techniques. We present an alternative readout scheme with the potential to rival current readout technologies. This readout scheme uses novel position encoding strategies such as charge comparison amongst a subset of readout electrodes combined with a signal timing method to obtain low resolution charge measurement which enables it to provide high spatial resolution at high count rates. We describe results of a readout simulation using measured data from an electronic breadboard to predict performance. We discuss how this scheme could be adapted to provide the capability for simultaneous event imaging and higher count rates by implementing parallelism.

A “Universal Time” system for ASDEX upgrade

For the new generation of intelligent controllers for plasma diagnostics, discharge control and long-pulse experiment control a new time system supporting steady state real-time operation has been devised. A central unit counts time at nanosecond resolution, covering more than the experiment lifetime. The broadcast time information serves local units to perform application functions such as current time readout, trigger generation and sample time measurement. Time is treated as a precisely measured quantity like other physical quantities. Tagging all detected events and sampled values with measured times as [value; time]-entities facilitates real-time data analysis, steady state protocolling and time-sorted archiving.

A fast readout using switched current techniques for a DEPFET-pixel vertex detector at TESLA

A fully depleted silicon detector with a first amplifying transistor integrated in every pixel (DEPFET) is a promising proposal for the pixel-based vertex detector at TESLA. The DEPFET offers good spatial resolution, an excellent signal-to-noise ratio and low power consumption in a row-wise operation mode. A readout concept for a DEPFET pixel array matching the requirements at TESLA is described. In order to meet the operation specifications at TESLA ( 50 MHz row rate), a readout architecture based on current mode techniques (Switched Current) is presented. It contains stand alone zero suppression offering a triggerless operation. The core of the readout chip, a fast operating current memory cell, is discussed in detail. The results of a first prototype chip, CURO I (CUrrent ReadOut), show that the requirements for TESLA are achievable.

Spin Effects in Lateral Quantum Dots

We present the review of our work on spin effects in single lateral quantum dots with the emphasis on the results of Coulomb blockade spectroscopy studies. Realization of a spin-based quantum bit proposal in a lateral quantum dot is discussed. Described are the ways of isolating a single electron spin in a dot containing only one as well as many electrons. Demonstrated is a current readout of spin transitions in a dot by means of spin blockade spectroscopy due to spin polarized injection/detection mechanism in a lateral dot. Discussed are transitions induced both by changing a magnetic field and a number of electrons in a dot with the emphasis on the effects observed close to filling factor in a dot ν = 2.

Filtered X Ray Beam Dosimetry from 10-3 to 102 Gy Dose Range by using Phototransistors

Low-cost, commercially available phototransistor-type semiconductor devices have been tested for monitoring filtered X ray beam dose. A Pantak X-ray unit was used to generate aluminium filtered X ray beams from 60 to 120 kV potentials. The analysis of the radiation detection behaviour as a function of the X ray tube parameters (peak kilovoltage and electrical current) are presented. The changes of the phototransistor electronic parameters have been evaluated and the results indicate that phototransistors can be used as X ray detectors for dose estimation in two different ways: electrical current read-out from 1 to 100 mGy dose range, and the changing of the radiation detection sensitivity in the dose range from 0.1 to 100 Gy. In addition, the devices show high reliability with no sign of substantial performance degradation with use and, in certain dose ranges, the cumulative dose evaluations could be performed up to 10,000 times with no need for re-calibration.

Temperature Effect on AlN/SiO2 Gate pH-Ion-Sensitive Field-Effect Transistor Devices

The temperature effect was investigated for the ion-sensitive field-effect transistor (ISFET) devices with an aluminum nitride (AlN) gate insulator. The AlN thin film was prepared on the reference electrode/electrolyte/AlN thin film/SiO2/p-Si substrate structure by radio frequency sputtering technology. The current–voltage characteristics of the AlN/SiO2 gate ISFET were obtained at various temperatures and the pH sensitivities were calculated in the buffer solutions range of pH=1-11. The experimental results show that the pH sensitivities were 48.38, 52.5, 53.83, 54.46, 56.0, 56.36, and 57.25 mV/pH for 5-65±0.1°C (step 10°C). The temperature coefficient of sensitivity (T.C.S.) was determined to be 0.130 mV/pH°C. In addition, the constant voltage constant current (CVCC) readout circuit was used to measure the gate versus source output voltage in various pH buffer solutions at different ambient temperatures, which reveals the same temperature-dependent characteristics of the ISFET.

Spin polarized injection into a quantum dot by means of the spatial separation of spins

We describe transport measurements on a small lateral dot involving spin polarized injection and detection. The novel layout of the lateral dot allows its electron occupation number to be reduced to 0 from 60 while maintaining operating tunneling barriers. The spin polarized injection occurs above (0.4 T) due to the presence of spin resolved edge states in the two dimensional electron gas which form the leads to the quantum dot. We demonstrate the consequences of spin polarized leads by focusing on two spin properties of the quantum dot close to filling factor, ν, 2. Firstly, we illustrate an alternating odd/even occupation number effect due to spin blockade through current readout at ν=2. Secondly, we detect spin transitions directly at fixed electron number in the quantum dot as the magnetic field is lowered away from ν=2. The experimental results are explained by a comparison to theoretical calculations of the ground states in the different regimes. The current readout process is one of the requirements of a quantum dot based spin qubit quantum computer.