Voltage Readout Research Articles

Contribution of afferent pathway to vagal nerve stimulation-induced myocardial interstitial acetylcholine release in rats.

Vagal nerve stimulation (VNS) has been explored as a potential therapy for chronic heart failure. The contribution of the afferent pathway to myocardial interstitial acetylcholine (ACh) release during VNS has yet to be clarified. In seven anesthetized Wistar-Kyoto rats, we implanted microdialysis probes in the left ventricular free wall and measured the myocardial interstitial ACh release during right VNS with the following combinations of stimulation frequency (F in Hz) and voltage readout (V in volts): F0V0 (no stimulation), F5V3, F20V3, F5V10, and F20V10. F5V3 did not affect the ACh level. F20V3, F5V10, and F20V10 increased the ACh level to 2.83 ± 0.47 (P < 0.01), 4.31 ± 1.09 (P < 0.001), and 4.33 ± 0.82 (P < 0.001) nM, respectively, compared with F0V0 (1.76 ± 0.22 nM). After right vagal afferent transection (rVAX), F20V3 and F20V10 increased the ACh level to 2.90 ± 0.53 (P < 0.001) and 3.48 ± 0.63 (P < 0.001) nM, respectively, compared with F0V0 (1.61 ± 0.19 nM), but F5V10 did not (2.11 ± 0.24 nM). The ratio of the ACh levels after rVAX relative to before was significantly <100% in F5V10 (59.4 ± 8.7%) but not in F20V3 (102.0 ± 8.7%). These results suggest that high-frequency and low-voltage stimulation (F20V3) evoked the ACh release mainly via direct activation of the vagal efferent pathway. By contrast, low-frequency and high-voltage stimulation (F5V10) evoked the ACh release in a manner dependent on the vagal afferent pathway.

A Self-Adaptive Measurement System for IGBT Collector Current Using Package Parasitics

Insulated gate bipolar transistor (IGBT) collector current measurement based on the package parasitics between the power emitter (E) and the Kelvin emitter (E') is a lossless and real-time monitoring method. A step to improve accuracy is to precisely match the time constant (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> × C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> ) of the measurement circuit against the package parasitics (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EE'</sub> /R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EE'</sub> ). This article proposes an automated time constant matching method to realize the tuning of R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> × C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> to L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EE'</sub> /R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EE'</sub> , and a detection circuit to continuously measure the IGBT collector current using the package parasitics. In the proposed method, the Miller plateau voltage is first sampled, and a polynomial curve fit is carried out to determine the fitting parameters associated with the IGBT collector current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> ). A programmable resistor R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> is then adjusted automatically based on the step response of the readout voltage until the time constant is matched. A ratio between the readout voltage and a known I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> is then calculated based on the Miller plateau voltage. The proposed system is verified using a field-programmable gate array controller and discrete components. Experimental results confirmed the functionality of the proposed method, showing that the readout voltage versus I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> relationship has good agreement in the range of 0-165 A, with less than 3% error. The proposed method can also be used for overcurrent protection with a detection time of less than 0.7 μs.

A novel low-cost turbidity sensor for in-situ extraction in TCM using spectral components of transmitted and scattered light

Abstract Compared with light intensity measurements of turbid liquids based on direct or lock-in amplification methods, the square excitation method (SEM) can be used to obtained abundant information from both the time- and frequency-domains. Voltage-based turbidimetry in the time domain (The voltage readout here refers to the signal obtained directly by the photodetector followed by an amplifier and is a function of the light intensity attenuated by scattering and absorption effects) is subject to measurement error because of the heterogeneous size distribution of suspended particles, fluctuations of the light source, and measurement noise. In this work, a novel low-cost turbidity sensor was proposed by combining spectral component extraction (SCE) with the transmitted (It) and scattered (Is) light signals and their ratio (It/Is). A near-infrared Light Emitting Diode (NIR-LED) at 860 nm was employed as the light source to reduce the system cost. Two independent preprocessing channels composed of a photodiode, a transimpedance amplifier, and a band-pass filter converted the modulated light to signals of a suitable scale. For conversion of the conditioned analog signals, a 16-bit analog-to-digital converter was used and the signal was further processed using a high-performance microcontroller (STM32F405). The SCE algorithm and turbidity correlation were implemented via the integrated digital-signal-processer combined with Fast Fourier Transform digital algorithm. Averaging of multiple measurements further improved the measurement precision when using the first, third, and fifth spectral components that were related to a known turbidity. The calibration measurements for the sensor revealed that the correlation coefficients from the linear fitting were reliable and satisfactory when using It, Is, and (It/Is). Additionally, validation measurements further demonstrated that the proposed sensor had low measurement error. The maximum measured error was 6% for a turbidity of 10 NTU while the lowest relative error was 0.4% for the 280 NTU solution. The results demonstrate that the sensor has potential for automatic in-situ turbidity measurement applications, particularly for in-situ extraction processes used in Traditional Chinese Medicine.

Probing magnetism of individual nano-structures using Nb [formula omitted]-SQUIDs in hysteresis free mode

The magnetization reversal of an individual magnetic nano-structure has been best studied using a μ-SQUID. An optimum inductive shunt helps in eliminating the hysteresis in μ-SQUID’s current voltage characteristics, giving thus a direct voltage readout of magnetic flux with high bandwidth and sensitivity. Here we report on a new μ-SQUID magnetometry setup for studying the magnetism of individual magnetic nano-structures. The switching field anisotropy of Permalloy nano-needles was studied using both hysteretic and non–hysteretic μ-SQUID modes. The observed anisotropy fits well the magnetization reversal through curling mode under the Néel-Brown model as well as micromagnetic simulations. The latter show a reversal through vortex nucleation and annihilation whose signatures we observe through minor hysteresis loops in experiments. Some preliminary magnetization reversal studies on Fe3O4 nano-particles using a non–hysteretic μ-SQUID mode are also briefly discussed.

Planar Dual Gate GaN HEMT Cascode Amplifier as a Voltage Readout pH Sensor With High and Tunable Sensitivities

AlGaN/GaN high-electron-mobility transistor (HEMT) based pH sensors have the advantages of fast response and high stability, and can be used in harsh environments. This paper presents a pH sensor based on a planar dual-gate AlGaN/GaN HEMT cascode amplifier, which can increase the pH sensitivity for about 45 times from 45 mV/pH to 2.06 V/pH with linearity of 1.27%. The results indicate that it is possible to improve the pH sensitivity at the origin of detecting instead of the subsequent complex amplifier circuits. The proposed device has also shown the capacity to adjust the sensor’s sensitivity by changing the gate voltage and the resistance values for various pH ranges of different measuring requirements.

Electrical readout/characterization of single crystal diamond (SCD) cantilever resonators

We report on the electrical readout of the resonance frequency from single crystal diamond (SCD) cantilever resonators. Due to the deep nature of the dopants in SCD, metallic electrodes with nanometer thickness are deposited on the SCD resonators as piezoresistor for sensing. A cantilever sample with resonance frequency 411.48 kHz and Q factor around 16,000 at RT is demonstrated through the electrical readout. Because of the thin film nature of the sensing electrodes, little energy dissipation is imposed to the SCD cantilever. Frequency shifting due to the change of readout voltage is also investigated. The present work provides the avenue for the applications of SCD MEMS sensors with other circuits.

Control of the Boundary between the Gradual and Abrupt Modulation of Resistance in the Schottky Barrier Tunneling-Modulated Amorphous Indium-Gallium-Zinc-Oxide Memristors for Neuromorphic Computing

The transport and synaptic characteristics of the two-terminal Au/Ti/ amorphous Indium-Gallium-Zinc-Oxide (a-IGZO)/thin SiO2/p+-Si memristors based on the modulation of the Schottky barrier (SB) between the resistive switching (RS) oxide layer and the metal electrodes are investigated by modulating the oxygen content in the a-IGZO film with the emphasis on the mechanism that determines the boundary of the abrupt/gradual RS. It is found that a bimodal distribution of the effective SB height (ΦB) results from further reducing the top electrode voltage (VTE)-dependent Fermi-level (EF) followed by the generation of ionized oxygen vacancies (VO2+s). Based on the proposed model, the influences of the readout voltage, the oxygen content, the number of consecutive VTE sweeps on ΦB, and the memristor current are explained. In particular, the process of VO2+ generation followed by the ΦB lowering is gradual because increasing the VTE-dependent EF lowering followed by the VO2+ generation is self-limited by increasing the electron concentration-dependent EF heightening. Furthermore, we propose three operation regimes: the readout, the potentiation in gradual RS, and the abrupt RS. Our results prove that the Au/Ti/a-IGZO/SiO2/p+-Si memristors are promising for the monolithic integration of neuromorphic computing systems because the boundary between the gradual and abrupt RS can be controlled by modulating the SiO2 thickness and IGZO work function.

Improved Planar InAs Avalanche Photodiodes With Reduced Dark Current and Increased Responsivity

Indium Arsenide (InAs) infrared photodiodes provide high quantum efficiency in the wavelength range of 1.0–3.0 μm. Planar diode configuration has been adopted to reduce surface leakage. In this work, new fabrication procedures for planar InAs avalanche photodiodes (APDs) are reported. Beryllium (Be) ions were implanted into InAs at a relatively low energy of 34 keV. Effects of duration of post implant annealing on the electrical characteristics of InAs APDs were investigated. It was found that a combination of post implant annealing at 500 °C for 15 min and a shallow surface etch produces planar APDs with good characteristics (room temperature dark current density of 0.52 A/cm2 at −0.2 V and external quantum efficiency of 51% at 1520 nm at −0.3 V). These represent a 3 times reduction in dark current and 1.4 times increase in responsivity, compared to earlier Be-implanted planar InAs APDs. The APDs’ avalanche gain characteristics remain similar to those from earlier reports, with a gain of 4 at a relatively low operating bias of 5 V. This suggests the potential of integrating InAs APDs with low voltage readout integrated circuits (ROIC) for development of infrared imaging arrays. The data reported in this paper is available from the ORDA digital repository (DOI: 10.15131/shef.data.6955037).

Voltage readout from a piezoelectric intracochlear acoustic transducer implanted in a living guinea pig

The ability to measure the voltage readout from a sensor implanted inside the living cochlea enables continuous monitoring of intracochlear acoustic pressure locally, which could improve cochlear implants. We developed a piezoelectric intracochlear acoustic transducer (PIAT) designed to sense the acoustic pressure while fully implanted inside a living guinea pig cochlea. The PIAT, fabricated using micro-electro-mechanical systems (MEMS) techniques, consisted of an array of four piezoelectric cantilevers with varying lengths to enhance sensitivity across a wide frequency bandwidth. Prior to implantation, benchtop tests were conducted to characterize the device performance in air and in water. When implanted in the cochlea of an anesthetized guinea pig, the in vivo voltage response from the PIAT was measured in response to 80–95 dB sound pressure level 1–14 kHz sinusoidal acoustic excitation at the entrance of the guinea pig’s ear canal. All sensed signals were above the noise floor and unaffected by crosstalk from the cochlear microphonic or external electrical interference. These results demonstrate that external acoustic stimulus can be sensed via the piezoelectric voltage response of the implanted MEMS transducer inside the living cochlea, providing key steps towards developing intracochlear acoustic sensors to replace external or subcutaneous microphones for auditory prosthetics.

Design, modelling and system level simulations of DRIE-based MEMS differential capacitive accelerometer

The paper presents design, analytical modelling and system level simulations of a highly sensitive single-axis in-plane Micro-Electro-Mechanical-Systems (MEMS) differential capacitive accelerometer. The designed accelerometer is Deep-Reactive-Ion-Etching (DRIE)-based with Silicon-on-Insulator (SOI) wafer technology. Analytical models have been derived for frequency as well as transient response analysis. For system level simulations, accelerometer model were extracted from MEMS+® and further integration for the readout electronics were performed using MATLAB Simulink® module. The accelerometer has response time of 0.7 ms and settling time of 5 ms. The accelerometer has the displacement sensitivity of 0.121 μm/g, capacitive sensitivity of 225 fF/g and electrical sensitivity of 0.34 V/g for MS3110 capacitive to voltage readout circuitry, with a resolution of better than 1 mg. The device shows very less non-linearity (~ 0.3%) in the operating range of ± 5 g with a bandwidth of 100 Hz. The simulation results of designed open-loop readout circuitry to read the applied acceleration in terms of voltage are also presented.

Strain-mediated all-magnetoelectric memory cell

Downscaling of magnetoelectric random access memory device (MELRAM) is considered by studying an example of the hybrid structure based on ferroelectric-magnetostrictive metal. Elastic mechanism of magnetoelectric interaction is analyzed by numerical modeling taking into account inhomogeneous distribution of anisotropic strain, ferroelectric polarization and electric field. The proposed shape of the cell allows to decrease the inhomogeneity of the strain in the magnetic subsystem and to achieve remarkable dynamic characteristics for a nanometric device sized nm3: we adopted an input voltage of V0 = 90 mV and obtained a switching time tS = 1.1 ns, an output readout voltage VME = 4.7 mV, and an ultra-low energy consumption 13 aJ/bit.

AlGaN/GaN pressure sensor with a Wheatstone bridge structure

In this work, a Wheatstone bridge-type pressure sensor based on AlGaN/GaN heterostructure was fabricated for the first time. The pressure sensor consisted of four gateless high electron mobility transistors (HEMTs) on a 585 μm depth circular membrane, in which 15-μm-thick silicon substrate was left. Direct voltage readout was realized in the AlGaN/GaN pressure sensor, which exhibited a non-linearity of 0.6% with a sensitivity of 1.25 μV/kPa/V over a wide pressure range from 0.1 MPa to 5 MPa. Because of the in-plane isotropic properties, the working mechanism in the AlGaN/GaN pressure sensor is found to be quite different from the silicon-based sensor. Although the resistances of the four gateless HEMTs all increased with enlarging pressure, the changes of neighboring resistors varied with alignments under the piezoelectric effects. Finally, voltage linear readout was realized by the differential operation of Wheatstone bridge circuit.

An Analog Front End ASIC for Cardiac Electrical Impedance Tomography.

In this paper, an end-to-end CMOS application specific integrated circuit (ASIC) for readout channel in a cardiac electrical impedance tomography system is presented. The ASIC consists of an integrated current driver for current injection, an instrumentation amplifier, variable gain amplifier at the analog front end for voltage readout from electrodes, and an on-chip 10-bit successive approximation register analog to digital converter with serial peripheral interface. The ASIC is fabricated in the CMOS 0.18 $\mu$ m process with a supply voltage of 3.3 V. Amplitude and phase extraction of the voltages is performed in the digital domain with a matched filter. A fully integrated solution for use in multiple electrode system is demonstrated. The readout chain in the ASIC achieves a minimum signal-to-noise ratio of 71dB over the frequency range of 500 Hz-700 kHz, while maintaining an average accuracy of 99.7 $\%$. Frame rates of 21 frames per second for a 32 electrode system is feasible, and the ASIC has an overall power consumption of 11.8 mW.

Reversible Negative Resistive Switching in an Individual Fe@Al2O3 Hybrid Nanotube for Nonvolatile Memory.

Hybrid nanostructures can show enormous potential in different areas because of their unique structural configurations. Herein, Fe@Al2O3 hybrid nanotubes are constructed via a homogeneous coprecipitation method followed by subsequent annealing in a reducing atmosphere. The introduction of zero band gap Fe nanocrystals in the wall of ultrawide band gap Al2O3 insulator nanotubes results in the formation of charge trap centers, and correspondingly a single hybrid nanotube-based two-terminal device can show reversible negative resistive switching (RS) characteristics with symmetrical negative differential resistance (NDR) at relatively high operation bias voltages. At a large bias voltage, holes and electrons can be injected into traps at two ends from electrodes, respectively, and then captured. The bias voltage dependence of asymmetrical filling of charges can lead to a reversible variation of built-in electromotive force, and therefore the symmetrical negative RS with NDR arises from two reversible back-to-back series bipolar RS. At a low readout voltage, the single Fe@Al2O3 hybrid nanotube can show an excellent nonvolatile memory feature with a relatively large switching ratio of ∼30. The bias-governed reversible negative RS with superior stability, reversibility, nondestructive readout, and remarkable cycle performance makes it a potential candidate in next-generation erasable nonvolatile resistive random access memories.

A 0.5 μA/Channel front-end for implantable and external ambulatory ECG recorders

There is an increasing demand for low power, low voltage, and small size analog readout bio-potential systems. This paper presents an analog front-end for measuring the intra-cardiac signals in implantable and also external ambulatory ECG cardiac recording applications. The analog front-end benefits from voltage to frequency conversion without conventional analog to digital conversion and thereby achieves a very low power consumption. The frequency averaging digital reconstruction makes an intrinsic low pass filter of which the cut-off frequency changes with the averaging interval and eliminates the need for an analog filter in this system. Furthermore, this feature enables the development of a general purpose analog readout bio-potential measurement system with programmable bandwidth. The proposed IC is fabricated in a 0.18 μm CMOS process and occupies 0.396 mm2. It can measure intra-cardiac bio-potentials with 9.2-bit resolution while consuming just 0.5 μA per channel from a 1 V supply. The input referred noise of the intra-cardiac signal readout channel is 2 μVrms.

Study of monolithic integrated solar blind GaN-based photodetectors

Monolithic integrated solar blind devices on the GaN-based epilayer, which can directly readout voltage signal, were fabricated and studied. Unlike conventional GaN-based photodiodes, the integrated devices can finish those steps: generation, accumulation of carriers and conversion of carriers to voltage. In the test process, the resetting voltage was square wave with the frequency of 15 and 110 Hz, its maximal voltage of ∼2.5 V. Under LEDs illumination, the maximum of voltage swing is about 2.5 V, and the rise time of voltage swing from 0 to 2.5 V is only about 1.6 ms. However, in dark condition, the node voltage between detector and capacitance nearly decline to zero with time when the resetting voltage was equal to zero. It is found that the leakage current in the circuit gives rise to discharge of the integrated charge. Storage mode operation can offer gain, which is advantage to detection of weak photo signal.

A Coherent Receiver Based on SIM for Quantum Communication

In this letter, we propose theoretically a coherent receiver based on solid-state impact-ionization multiplier (SIM) for quantum communication. In the newly proposed coherent receiver, the balanced photodetector (BPD) is used as a current source connected to the SIM. The signal from the BPD is fed into the SIM, where it is amplified through a desirable avalanche process, which is similar to the avalanche photodiodes, and can then be fed into a transimpedance amplifier for voltage readout. Compared with the conventional coherent receiver with only coherent gain, the signal gain of the proposed coherent receiver consists of two parts, the coherent gain produced by the local oscillator (LO) and the avalanche gain produced by the SIM, so the LO power can be decreased to avoid the saturation of the BPD without sacrificing the signal gain. What is more, the proposed receiver can operate at a higher bandwidth by optimizing the structure of the coherent receiving end and redesigning the geometry of the SIM.

Portable Cyanobacteria Detection Fluorometer with Current-conveyor Transimpedance Amplifiers

A portable fluorometer has been developed for cyanobacteria detection by exploiting commercially available low-cost photodiodes. Particularly, the front-end detection circuit was integrated on-chip by using a 0.11-μm CMOS process to realize the high transimpedance gain of 99.7 dBΩ with low current consumption of 1.4 mA from a single 1.5-V supply, hence providing a low-power solution with small form-factor in the applications of portable cyanobacteria detection. For measuring fluorescence intensity of cyanobacteria, two quantum dots of QDSUB565/SUB and QDSUB655/SUB were employed into a NanoGene assay for mcyD gene(synthetase of toxic microcystin) detection of Microcystis aeruginosa, resulting in two different readout voltages. Various operational parameters (e.g. distance, angle between laser emission and vial sample, etc) were investigated for the proposed fluorometer. Measurements demonstrated that the mcyD gene hybridized with QDSUB565/SUB and QDSUB655/SUB was quantitatively detected, i.e. the normalized output voltage (QDSUB655/SUB/QDSUB565/SUB) was linearly proportional to the mcyD gene copy numbers (y = 0.25 log x – 0.25). Besides, the wireless transfer of the quantitative data was performed via Bluetooth.

Determination of Cu(II) in environmental water samples using polymer inclusion membrane-TAC optode in a continuous flow system

This study describes the selective determination of copper (II) using the recently developed polymer inclusion membrane (PIM) in a river water system via a continuous flow (CF) system. The PIM is composed of 42% di(2-ethlyhexyl) phosphoric acid (D2EHPA) as the carrier, 8% dioctyl phthalate (DOP) as the plasticizer and 49% poly(vinyl chloride) (PVC) as the base polymer. The colorimetric reagent that is used for the spectrophotometric determination of copper (II) is 1% 2-(2-thiazolylazo)-p-cresol (TAC). In this system, copper (II) is extracted into the PIM as the copper-D2EHPA complex which afterwards reacts with TAC producing green copper −TAC complex. The quantitative measurements are conducted by using light emitting diode (LED) and light dependent resistor (LDR) connected to a voltmeter. Results are obtained through the voltage readout on the computer. Under optimal conditions, the sensor has a limit of detection (LOD) of 0.10 mg L−1 and a limit of quantitation (LOQ) of 0.35 mg L−1. The CF-PIM-TAC system was successfully used in the determination of Cu(II) in river systems near mining sites.

Multi-ramp reference voltage PWM imaging scheme with enhanced dynamic range and correlated double sampling

A multi-ramp reference voltage readout scheme for CMOS digital pixel sensor (DPS) based on pulse width modulation (PWM) imaging is proposed to extend the dynamic range (DR) and eliminate the fixed pattern noise (FPN). The exposure period is divided into two sampling stages, the FPN and some random noise can be eliminated by time-domain correlated double sampling (CDS). The multiple ramps are introduced to obtain a larger DR although the integration time is limited. A behavioral model of the PWM DPS with this scheme is simulated with MATLAB, the DR, photoresponse and FPN are analyzed versus the design parameters. A DPS with the multi-ramp reference can achieve 103.06dB DR with CDS at 100fps, 16-bit memory depth and 1.8V power supply. And the DR can be further extended to 138.49dB with a single sampling at high light condition. FPN can drop to less than 1LSB after the CDS operation from 3.97% without CDS.