Low Bias Current Research Articles

Beam tests of SNSPDs with 120 GeV protons

We report the test results for a 120GeV proton beam incident on superconducting nanowire particle detectors of various wire sizes. NbN devices with the same sensitive area were fabricated with different wire widths and tested at a temperature of 2.82K. The relative detection efficiency was extracted from bias current scans for each device. The results show that the wire width is a critical factor in determining the detection efficiency and larger wire widths than 400nm leads to inefficiencies at low bias currents. These results are particularly relevant for novel applications at accelerator facilities, such as the Electron-Ion Collider, where cryogenic cooling is readily available.

A Comparative Study on Picoammeter Designs as Alternatives for Nuclear Reactor Power Measurement Systems

Abstract The study investigates the picoammeter, a highly sensitive current measurement device capable of measuring currents in the picoampere (pA) range. It discusses the typical amplification technique in picoammeters, utilizing an Op-Amp in a trans-impedance amplifier (TIA) circuit to convert the current into a voltage signal. The paper explores the impact of different IC Op-Amps on the picoammeter’s performance, evaluating AD549, MAX4230, LMC662, TLV272, and MCP6001. The result reveals that AD549 Op-Amp ICs are more suitable for picoammeter design due to their low noise performance and low input bias current. Noise output and AC stability are assessed through numerical analysis and simulations using a circuit simulator. The resulting picoammeter exhibits low noise, high sensitivity, and precise measurement accuracy, making it an optimal choice for precise low-current measurements in CIC detectors.

Low bias charge transport in DNA.

The low-bias current-voltage technique was utilized to study charge transport in single-stranded DNA (ssDNA), assessing the method's effectiveness for future studies aimed at estimating the degree of mutation or DNA damage. In the paper, we showed that charge carrier transfer processes in ssDNA can be precisely monitored using low-bias currents. We used negative differential resistance and the Fowler-Nordheim model to differentiate the charge transport mechanisms observed in a device composed of gold electrode-thiol-ssDNA junctions. It was possible to distinguish the processes at the two junctions (Au/thiol and thiol/DNA) due to their distinct current-voltage characteristics. We observed positive charge carrier tunneling, which we attribute to oxidation and reduction processes in the nucleobases of the ssDNA. Our results suggest that even minor changes in DNA chains can be accurately detected using the described methodology.

Current dependence of the low bias resistance of small capacitance Josephson junctions

The dc current-voltage characteristics of small Josephson junctions reveal features that are not observed in larger junctions, in particular, a switch to the finite voltage state at current values much less than the expected critical current of the junction and a finite resistance in the nominally superconducting regime. Both phenomena are due to the increased sensitivity to noise associated with the small capacitance of the Josephson junction and have been extensively studied a few decades ago. Here I focus on the current bias dependence of the differential resistance of the junction at low current bias in the nominally superconducting regime, using a quantum Langevin equation approach that enables a physically transparent incorporation of the noise environment of the junction. A similar approach might be useful in modeling the sensitivity of superconducting qubits to noise in the microwave regime.

Analysis of Two Stage CMOS Operational Amplifier in 90nm CMOS Technology

Abstract: Operational amplifier circuits are used in computation, instrumentation and other applications. Precision op-amps previously used in instrumentation are now-a-days being used in industrial and automotive applications. Hence, there always exists a need for better precision op-amps. It should operate under a wide temperature range. Nowadays, due to the industry trend of applying standard process technologies to implement both analog circuits and digital circuits on the same chip, Complementary Metal-Oxide Semiconductor (CMOS) technology has become dominant over bipolar technology for analog circuit design in a mixed-signal system. Two-stage Op-Amp is one of the most commonly used Op-Amp architectures. In this work an operational amplifier based on CMOS is presented whose input depends on its bias currents which is 20µA and designed using 180nm and 90nm technologies. In sub-threshold region due to unique behavior of the MOS transistors not only allows a designer to work at low voltages and it also allows operating at low input bias currents. Most CMOS Op-Amps are designed for specific on-chip applications and are only required to drive capacitive loads of a few pf. In this proposed work, design of a two stage fully differential CMOS operational amplifier is presented and simulations are carried out in 180nm and 90nm technologies for various parameters. The simulation is to be carried out using Cadence Virtuoso Tool.

Bulk Cum QFG-Driven FVF Double Recycling Current Mirror Subthreshold OTA Based CCII+ Cell and Applications

This paper presents a low-voltage low-power second generation CCII+ cell using bulk-driven FVF class AB mode operated double recycling current mirror OTA. The OTA is used in the input core of CCII+ cell utilizes bulkcum Quasi Floating Gate (QFG)-based voltage to current converter and Partial Positive Feedback (PPF) to enhance the performance of the circuit. The circuit permits closely railto- rail input common mode range, high output current drive capability with low dual power supply of ± 0.25 V. This circuit produces low input referred noise of 1.65 μV/sqrt Hz, dissipates ultra-low power of 342 nW and is suitable for lowfrequency applications, such as bio-signal processing. Further, to validate this design, a MISO type voltage mode biquadratic filter and voltage mode two phase quadrature oscillator are currently being implemented using this CCII+ cells. The circuit is simulated in tanner EDA tools using 180 nm n-tub CMOS process technology with low bias current of 18 nA.

Integrated biosensing system of electrochemistry and electrophysiology for cortisol and skin conductance analysis on smartphone

High level of mental stress will lead to negative psychological and health consequences, such as insomnia, depression, and cardiovascular disease, which will increase the suicide rate and affect social stability. Mental stress has been proved to be related to biomarkers cortisol and skin conductance, and reflects the complementary advantages of stress monitoring. Based on electrochemistry and electrophysiology analysis technology, combined with microelectronic design and biosensors, this paper constructed an integrated physiological and biochemical sensing system, and an intelligent user interaction system. Firstly, a molecularly imprinted biosensor with gold nanoparticles (AuNPs), prussian blue (PB), and polypyrrole (PPy), achieved highly sensitive detection of cortisol in the range of 1–10000 ng/mL and demonstrating good specificity. The cortisol detection unit used differential pulse voltammetry (DPV) method by dual power amplifier chip AD8674, which was a precision operational amplifier with low noise, low input bias current, and unit gain stability. Then, the skin conductance detection unit was mainly composed of a pulse width modulation (PWM) drive circuit, which was designed to achieve a 100 Hz voltage output. The integrated system was designed with microcontroller module, transimpedance amplifier (TIA) module, power management module, signal transmission module, cortisol and skin conductance detection module, which was suitable for constructing precision voltage control and weak current signal conditioning. Finally, based on the software and hardware platform of smartphones, an intelligent analysis system was developed to improve the portability and user interaction convenience. Our system achieved the physiological and biochemical joint detection for the first time, showing enormous application potential in future multimode sensing monitoring.

Low-Dropout Voltage Regulator Designed with Nanowire TFET with Different Source Composition Experimental Data

This paper presents the design of low-dropout volt-age regulators (LDO) using nanowire tunnel field-effect tran-sistors (TFETs) and nanowire MOSFET. The devices are mod-eled using lookup tables implemented with experimental measures of TFETs with different source compositions (Si, SiGe and Ge) and MOSFET. In order to compare the designs, the transistors of the differential amplifier in all LDOs is biased with gm/ID = 8 V-1 with a load of 1 μA and 10-pF. It is shown that all TFET based LDOs are stables without the need of a compensator capacitor (CC) even for higher load capacitance. For the MOSFET LDO, a CC of 5-pF capacitor was used. The study shows that the TFET based LDOs deliver higher effi-ciency due to the possibility to operate with low bias current. In the transient analysis it is shown that the TFET LDOs have lower overshoot but higher delay. The Ge-TFET LDO pre-sented settling times for load and line transient close to the MOSFET LDO with 15 μs and 30 μs. The SiGe-TFET LDO shows the best loop gain (60 dB), while the Si-TFET LDO deliv-ers lowest quiescent current (300 pA) and the Ge-TFET have the best GBW (70 KHz) and PSR (-52 dB). It is concluded that the TFET based LDOs can deliver specifications similar or bet-ter than the MOSFET LDO even without the need of CC and with less power consumption.

Efficient and Accurate Optical Signal Processing and Digitization System for High Speed Data Acquisition and Analysis

The evolution of optical fiber technology has expanded its utility beyond communication to encompass measurement. Key components include the light source, detection elements, and processing circuits. This paper describes a system for optical signal processing and digitization of light pulses, employing advanced components to enhance data acquisition and analysis performance. The optical signal processing phase employed the LF356N operational amplifier, offering attributes like low bias current, high bandwidth, and rapid settling time. Configured as a transimpedance amplifier, the opamp transformed light signals into corresponding analog voltage signals. Subsequently, the voltage signal underwent digitization using the AD976AN, a 16-bit ADC with advanced features such as high-speed data acquisition and an integrated clock. This ADC was controlled by a Teesny 3.6 board with a fast CPU clock speed of up to 256 MHz, greatly facilitating rapid data analysis and algorithm execution. The hardware circuit underwent meticulous design, simulation, and fabrication, followed by rigorous testing involving various distinct light sources with differing parameters. The digitized and computed parameter values (obtained after subjecting the ADC outputs to the suggested algorithm) exhibited a high degree of similarity in comparison to the observed values on the oscillo-scope.

Synthesis of a large area ReS2 thin film by CVD for in-depth investigation of resistive switching: effects of metal electrodes, channel width and noise behaviour.

The anisotropic crystal structure and layer independent electrical and optical properties of ReS2 make it unique among other two-dimensional materials (2DMs), emphasizing a special need for its synthesis. This work discusses the synthesis and in-depth characterization of a 1 × 1 cm2 large and few layered ReS2 film. Vibrational modes and excitonic peaks observed from the Raman and photoluminescence (PL) spectra corroborated the formation of a ReS2 film with a 1.26 eV bandgap. High resolution transmission electron microscopy (HRTEM) images and selected area electron diffraction (SAED) patterns inferred the polycrystalline nature of the film, while cross-sectional field emission scanning electron microscopy (FESEM) indicated planar growth with ∼10 nm thickness. The chemical composition of the film analysed through X-ray photoelectron spectroscopy (XPS) indicated the formation of a ReS2 film with a Re : S atomic ratio of 1 : 1.75, indicating a small amount of non-stoichiometric RexSy. Following the basic characterization studies, the ReS2 film was tested for resistive switching (RS) device application in which the effects of different metal electrodes (Pt/Au and Ag/Au) and different channel widths (200, 100, and 50 μm) were studied. The highest memory window equal to 108 was obtained for the Ag/Au electrode while Pt/Au showed a memory window of 102. RS for the former was ascribed to the formation of a conducting filament (CF) because of the migration of Ag+ ions, while defect mediated charge carrier transport led to switching in the Pt/Au electrode. Furthermore, the RHRS/RLRS ratio achieved in this work (108) is also of the highest magnitude reported thus far. Furthermore, a comparison of devices with Ag/Au electrodes but with different channel widths (50, 100 and 200 μm) gave insightful results on the existence of multiple resistance states, device endurance and retention. An inverse relationship between the retention time and the device's channel width was observed, where the device with a 50 μm channel width showed a retention time of 48 hours, and the one with a 200 μm width showed stability only up to 3000 s. Furthermore, low frequency noise measurements were performed to understand the effect of defects in the low resistance state (LRS) and the high resistance state (HRS). The HRS exhibited Lorentzian noise behaviour while the LRS exhibited Lorentzian only at low current bias which converged to 1/f noise at higher current bias.

Net 5.75 Gbps/2 m Single-Pixel Blue Mini-LED Based Underwater Wireless Communication System Enabled by Partial Pre-Emphasis and Nonlinear Pre-Distortion

Blue LEDs are cost-effective optical sources suitable for underwater optical wireless communication (UOWC) systems. However, the nonlinearity and the low-pass response of LEDs alongside the limited sensitivity of photodetectors constrain the capacity and reach of UOWC systems. Here we address these issues by means of a combined DSP scheme consisting of partial pre-emphasis and nonlinear pre-distortion. Partial pre-emphasis pre-compensates for the low-pass response of the system while relaxing the power reduction induced by a high peak-to-average power ratio, whereas nonlinear pre-distortion can effectively alleviate the LED nonlinearity with only marginal impact on the signal power. Further, it is found that the signal power and the signal SNR at the receiver can be improved by setting a low current bias for the mini-LED because of less saturated radiative recombination. The effectiveness of this combined DSP scheme and device conditioning approach is experimentally validated and enables the transmission of a net 5.75 Gb/s PAM-8 signal over 2 m of distance underwater, which, to our knowledge, is the highest net data rate achieved for single-pixel LED-based UOWC systems.

Modeling of Relative Intensity Noise in QD-VCSEL

In this paper, the dynamics and statics properties of a 1.3 m InAs/InGaAs Quantum-Dot (QD) vertical-cavity surface-emitting laser (VCSEL) have been investigated using a self-consistent coupled rate-thermal equations model. Results demonstrate that self-heating caused by current transition through the Bragg mirrors and active area of the laser produces temperature rise and deteriorates the performance of the laser where it is most apparent at higher temperatures. Although the minimum value of Relative intensity noise (RIN) and the turn-on delay and maximum value of the output power occurs at the same bias current, the maximum achievable 3-dB modulation bandwidth is obtained at lower bias currents. In addition, the larger aperture size and the greater number of QD layers modify the self-heating and enhance the efficiency and output characteristics of the laser where the rolled-off of the laser happens at higher bias currents.

An 11 mA Capacitor-Less LDO With 3.08 nA Quiescent Current and SSF-Based Adaptive Biasing

This brief presents an ultra-low power low-dropout (LDO) regulator with an experimental total quiescent current consumption of only 3.08 nA. The circuit is designed to operate with a load current in the range 0 - 11 mA. A novel adaptive biasing scheme based on a super source follower (SSF) structure is proposed, which measures the absolute voltage difference between the two inputs of the LDO’s error amplifier and modifies the biasing current accordingly. Thus, the transient response of the regulator is improved by counteracting the effect of using such a low bias current. The proposed LDO has been fabricated in a standard CMOS 180 nm process and the experimental characterization showed an outstanding performance in terms of maximum load current over quiescent current consumption ratio.

Investigation on the complex and tunable laser chaos generated by the microresonator optical combs injection

A novel method to generate high complexity and wavelength-tunable laser chaos is proposed by injecting nonlinear frequency combs from a microresonator (MR) into a semiconductor laser. The nonlinear dynamics and chaotic characteristics are simulated. The results show that chaos with permutation entropy of 0.997, spectral entropy of 0.953, spectrum bandwidth of 32.4 GHz, the flatness of 0.38 dB/GHz can be generated. Compared with the conventional optical feedback injection system and the phase conjugate feedback injection system, the MR injection system can generate better chaos with bandwidth enhancement and complexity improvement at lower bias currents. The time delay signature introduced by the MR can be completely concealed, which provides support for chaotic secure communication. Furthermore, the microresonator injection (MRI) system is flexible and expandable. Laser chaos with tunable wavelength can be generated by changing the working wavelength of the slave laser. And if multiple lasers with free spectral range interval are connected to MR parallelly, up to 93 high-performance chaotic carriers with a cross-correlation as low as about 0.1 can be realized in short, conventional, and long wavelength bands simultaneously. This scheme provides a foundation for multiple parallel chaotic carriers and large-capacity chaotic secure communication.

Impact of base bias current and incident optical power on the InP/InGaAs heterojunction phototransistor performances

In this article, the optical and electrical properties of NPN InP/InGaAs heterojunction bipolar phototransistor (HPT) are studied by two dimensional semiconductor simulation. The phototransistor is modelled using a numerical method, and the results are presented and discussed. This model is based on heterojunction bipolar transistor (HBT) model with the consideration of the optical beam effect. Responsivity of 12.62 A/W for 1100 nm light is achieved when the thickness of base layer is 50 nm. A good qualitative agreement of the numerical and analytical simulated value of both collector current and responsivity as a function of the wavelength with the existing experimental data was achieved. We present a comparative analysis of our obtained solutions at IB = 5 μA with that simulated at IB = 100 μA and we found that the value of optical power (Popt) giving high injection into a phototransistor at IB = 5 μA is three times higher than that at IB = 100 μA. The effects of both the base bias current and the incident optical power on the device performance are investigated. The simulation results, which are presented and compared at low, ideal and high base bias current, show that the highest photocurrent and optical gain are obtained when the base bias current reaches the ideal region. The HPT optical characteristics such as the electrical characteristics of HBT are affected by the high injection effect (Kirk effect).

Cryogenic readout of superconducting nanowire single-photon detectors using high-sensitivity adiabatic quantum-flux-parametron circuits

We have been developing readout interfaces for superconducting nanowire single-photon detectors (SSPDs) using adiabatic quantum-flux-parametron (AQFP) logic. AQFP circuits operate with low power consumption, low bias currents, and high sensitivity, and thus are suitable as readout interfaces for large SSPD arrays. In this study, we develop a high-sensitivity AQFP interface, consisting of a current transformer, comparator, and rising-edge detector. We systematically investigated the current sensitivity of the AQFP interface by operating an NbTiN SSPD with the interface in a 0.1 W Gifford–McMahon cryocooler. We compared the outputs from the AQFP interface with the direct outputs from the SSPD, thereby demonstrating a sensitivity of 3.5 μA, which is much smaller than that of the single-flux-quantum interfaces that we developed before.

A 1.2 V, 3.1% 3σ-accuracy thermal sensor analog front-end circuit in 12 nm CMOS process

This paper presents a 1.2 V high accuracy thermal sensor analog front-end circuit with 7 probes placed around the microprocessor chip. This analog front-end consists of a BGR (bandgap reference), a DEM (dynamic element matching) control, and probes. The BGR generates the voltages linear changed with temperature, which are followed by the data read out circuits. The superior accuracy of the BGR’s output voltage is a key factor for sensors fabricated via the FinFET digital process. Here, a 4-stage folded current bias structure is proposed, to increase DC accuracy and confer immunity against FinFET process variation due to limited device length and low current bias. At the same time, DEM is also adopted, so as to filter out current branch mismatches. Having been fabricated via a 12 nm FinFET CMOS process, 200 chips were tested. The measurement results demonstrate that these analog front-end circuits can work steadily below 1.2 V, and a less than 3.1% 3σ-accuracy level is achieved. Temperature stability is 0.088 mV/°C across a range from –40 to 130 °C.

Waveform analysis of a large-area superconducting nanowire single photon detector

Superconducting nanowire single photon detectors (SNSPDs) are typically used as single-mode-fiber-coupled single-pixel detectors, but large area detectors are increasingly critical for applications ranging from microscopy to free-space quantum communications. However, the long meander-line length of such large-area SNSPDs results in a proportionately large kinetic inductance that affects the waveform generated by the device. Here, we explore changes in the rising edge of the readout pulse for a single-pixel large-area SNSPD as a function of the optical spot size on the detector and compare to the rising edge of the dark-count waveform. We observe a bimodal distribution of bright-count rise times and show that the probability of a slow rise time increases in the limit of large spot sizes, indicative of a position sensitive response. Additionally, in the limit of low bias currents, the dark-count readout pulse is most similar to the large spot-size bright-count readout pulse, which suggests that dark counts arise from locations spanning the device. These results are consistent with a simple model of traveling microwave modes excited by single photons incident at varying positions along the length of the nanowire.

A Tunable CMOS IR-UWB Pulse Generator Based on Feedback Controlled Oscillator Switching

This brief presents a tunable Impulse-Radio Ultra-Wideband (IR-UWB) pulse generator based on feedback oscillator switching. The circuit provides a wide range of pulse amplitude and width tuning, thus enabling the required pulse shaping for a desired pulse repetition rate and/or a wireless transmission range. Feedback controlled switching prevents the potential omission of the UWB pulse generation and provides low UWB pulse energy variations at low bias currents and a wide temperature range, ensuring system robustness with respect to temperature variations. The pulse amplitude is tunable within 0.27 Vpp to 2.05 Vpp, while the pulse width tuning range is 1-6.5 ns. The total energy consumption of the IR-UWB pulse generator at the 50 Mpps pulse repetition rate is equal to 25.4 pJ/pulse for the pulse amplitude equal to 0.27 Vpp, while for the pulse amplitude equal to 2.05 Vpp, it is increased up to 99.8 pJ/pulse. The circuit occupies a core area of 0.56 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in a 0.18 μm CMOS technology.

Current Feedback Instrumentation Amplifier With Built-In Differential Electrode Offset Cancellation Loop for ECG/EEG Sensing Frontend

This work describes a compact and low-power current feedback instrumentation amplifier (CFIA) that can effectively eliminate differential electrode offset (DEO), amplifier input offset, and light motion artifacts. The proposed approach is using a local feedback loop in the first stage of the CFIA which can eliminate dc and low frequency offset whereas by-passes useful components such as EEG and ECG signals. As a result, the DEO and amplifier input offset can be eliminated in the first stage of the CFIA while still amplifying the desired signal components. This enables offset cancellation operation with low bias current that leads to higher energy efficiency compared to existing CFIA offset cancellation schemes. The proposed CFIA is implemented using CMOS 0.18-μm technology, that can eliminate up to 250-mV DEO with a supply voltage of 1.8 V. Measurement results show common mode rejection ratio (CMRR) 120 dB (without DEO) and 95 dB (with DEO of 250 mV) at 10 Hz, input noise 3.8 μVrms, power consumption 12.7 μW, and NEF 39 with core area of 73.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Furthermore, the actual EEG and ECG waveforms are obtained using the proposed CFIA under an actual clinical setting.