Sensor Interface Circuit Research Articles

Magnetostrictive bi-perceptive flexible sensor for tracking bend and position of human and robot hand

The sensor that simultaneously perceives bending strain and magnetic field has the potential to detect the finger bending state and hand position of the human and robot. Based on unique magneto-mechanical coupling effect of magnetostrictive materials, the proposed a bi-perceptive flexible sensor, consisting of the Co–Fe film and magnetic sensing plane coils, can realize dual information perception of strain/magnetic field through the change of magnetization state. The sensor structure and interface circuit of the sensing system are designed to provide high sensitivity and fast response, based on the input–output characteristics of the simulation model. An asynchronous multi-task deep learning method is proposed, which takes the output of the position task as the partial input of the bending state task to analyze the output information of the sensor quickly and accurately. The sensing system, integrating with the proposed model, can better predict the bending state and approach distance of human or robot hand.

A novel capacitive sensor interface based on a simple capacitance-to-phase converter

Abstract A novel room temperature capacitive sensor interface circuit is proposed and successfully tested, which uses a modified All-Pass filter architecture combined with a simple series resonant tank circuit with a moderate Q-factor. It is fashioned from a discrete inductor with small dissipation resonating with a grounded capacitor acting as the sensing element to obtain a resolution of ∆C ~ 2 zF in a capacitance range of 10 – 30 pF. The circuit converts the change in capacitance to the change in the phase of a carrier signal in a frequency range with a central frequency set up by the tank circuit’s resonant frequency and is configured to act as a close approximation of the ideal All-Pass filter. This cancels out the effects of amplitude modulation when the carrier signal is imperfectly tuned to the resonance. The proposed capacitive sensor interface has been specifically developed for use as a front-end constituent in ultra-precision mechanical displacement measurement systems, such as accelerometers, seismometers, gravimeters and gravity gradiometers, where moving plate grounded air gap capacitors are frequently used. Some other applications of the proposed circuit are possible including the measurement of the electric field, where the sensing capacitor depends on the applied electric field, and cost effective capacitive gas sensors. In addition, the circuit can be easily adapted to function with very small capacitance values (1 - 2 pF) as is typical in MEMS-based transducers.

Literature Review, Analysis of the Performance of Operational Amplifier Applied in Controlling Systems: Summary, Analysis, and Overview

As part of modern electronic technology, the operational amplifier is widely used in signal conditioning, sensor interface circuits, controller design, and actuator drives of automatic control systems. Improvement: In accurate controlling systems, factors such as linearity, noise performance, and stability directly influence the accuracy and speed of response of the whole system. Thus, it is vitally important for Improving the overall performance of automated control systems to learn and improve the performance of the operational amplifier. With the development of Industry 4.0 and intelligent manufacturing, modern controlling strategies such as adaptive control and intelligent controlling demand much more from the operational amplifier.

A High-Precision Bandgap Reference with Chopper Stabilization and V-Curve Compensation Technique.

The MEMS sensor converts the physical signal of nature into an electrical signal. The output signal of the MEMS sensor is so weak and basically in the low-frequency band that the MEMS sensor interface circuit has a rigorous requirement for the noise/offset and temperature coefficient, especially in the bandgap reference block. However, the traditional amplifier has low-frequency noise and offset voltage, which will decrease the precision of the bandgap reference. In order to satisfy the need of the MEMS sensor interface circuit, a high-precision and low-noise bandgap reference is proposed in this paper. A novel operational amplifier with a chopper-stabilization technique is adopted to reduce offset and low-frequency noise. At the same time, the V-curve compensation circuit is used to realize the second-order curvature compensation. The circuit is implemented under the 0.18 μm standard of the CMOS process. The test result shows that the temperature coefficient of the bandgap is 2.31 ppm/°C in the range of -40-140 °C, while the output voltage noise is only 616 nV/sqrt(Hz)@1 Hz and the power-supply rejection ratio is 73 dB@10 kHz. The linear adjustment rate is 0.33 mV/V for supply voltages of 1.2-1.8 V at room temperature, the power consumption is only 107 μW at 1.8 V power supply voltage, and the chip active area is 0.21 × 0.28 mm2.

Direct interface circuits for resistive sensors affected by lead wire resistances

This article proposes two novel circuits for the digital readout of resistive sensors with parasitic series resistances caused by the lead wire needed to connect remote sensors. Both circuits are based on so-called direct interface circuits (DICs). These circuits perform a resistance-to-time-to-digital conversion by adding some external components to a digital processors (DP). The new circuits are very simple since they only use a capacitor and two or three resistors, depending on the proposal. A single discharging of the capacitor provides two or three time measurements to estimate the resistance of the sensor, eliminating the influence of lead wire resistances. Using a single discharging process simultaneously reduces error sources, measurement time, and energy consumption. A circuit that uses an FPGA as DP to estimate resistances corresponding to several thermal sensors presents systematic errors below 0.15% or 0.12%, depending on the proposal, for a maximum measurement time of 1.09 ms.

Stable-operation design and fabrication results of a battery-less wireless-sensor interface IC with a switched-capacitor frequency-locked-loop circuit

This paper describes a method of designing a wireless-sensor interface integrated circuit that operates without a battery. Stable operation at low power is realized by integrating three kinds of circuit techniques: (i) a radio-frequency backscatter circuit for wireless sensing without power consumption, (ii) a sensor interface circuit with a frequency-locked loop for stable operation, (iii) and an energy harvester circuit with a power management function for battery-less operation. The circuit was fabricated using 0.13 μm CMOS process technology for design verification. We realized battery-less wireless sensing with intermittent operation and achieved high stability against process, voltage and temperature variations. The sensor information was obtained from the frequency variation of the radio-frequency backscatter signal. The integrated circuit was operated with radio-frequency signal power input exceeding −5 dBm. The integrated circuit dissipated less than 107.5 μA. The communication distance was 0.8 m at 920 MHz for 250 mW equivalent isotopically radiated power.

A Readout Circuit for MEMS Gas Sensor.

In recent years, the application of gas sensors is becoming more and more extensive. Driven by potential applications such as the Internet of Things, its technology development direction begins with miniaturization, integration, modularization, and intelligence. However, there is a bottleneck in the research of interface circuits, which restricts the development of gas sensors in volume, power consumption, and intelligence. To solve this problem, a MEMS gas sensor interface circuit based on ADC technology is proposed in this paper. Under the condition of the Huahong 110 nm process, the working voltage is 3.3 V, the resistance change of 100 Ω~1 MΩ can be detected, the conversion error is in the range of 0.5~1%, and the maximum power consumption is 986 μW. The overall layout area is 0.49 × 0.77 mm2. Finally, the correctness of the circuit function is verified by post-layout simulation.

A Power/Hardware-Efficient SiPM Readout IC Embedded in a Boost Converter for Mobile Radiation Dosimeters

A radiation detection system provides radiation intensity to protect human life from hazardous radiation. However, the prior portable radiation detection system (mobile radiation dosimeter) structures had a problem in that various subsystems had to be designed with complex circuits. First, since the radiation detector must be driven by a relatively high voltage, a high-efficient boost converter that can receive the battery voltage and generate a high bias voltage must be implemented. Second, sophisticated sensor interface circuits that can convert the analog signal generated by the radiation detector to digital value must also be implemented. To reduce the complexity of the mobile radiation dosimeters, a power- and hardware-efficient radiation detection system IC is presented for mobile radiation dosimeters. The current value of a silicon photomultiplier (SiPM) used as a radiation detector is sensed from the control information of a boost converter in the process of regulating a voltage to bias the SiPM. Due to this embedded sensing function, no additional hardware and power consumption are required for implementing and operating separate sensor interface circuits while providing sufficient radiation sensing performance. The implemented radiation detection system IC achieves 0.217- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> input referred noise performance over 1-kHz signal bandwidth and 10-mA maximum allowable linear input current range. In addition, the proposed dc–dc boost converter can generate a high enough voltage (∼27 V) to drive SiPM from a lithium-ion battery with an efficiency of 72%. The irradiation test with radiation check source ( <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs) demonstrates that the bias voltage is well regulated in the presence of high-energy radiation particles.

Electrophysiology-based Closed Loop Optogenetic Brain Stimulation Devices: Recent Developments and Future Prospects.

Closed loop optogenetic brain stimulation enhances the efficacy of the stimulation by adjusting the stimulation parameters based on direct feedback from the target area of the brain. It combines the principles of genetics, physiology, electrical engineering, optics, signal processing and control theory to create an efficient brain stimulation system. To read the underlying neuronal condition from the electrical activity of neurons, a sensor, sensor interface circuit, and signal conditioning are needed. Also, efficient feature extraction, classification, and control algorithms should be in place to interpret and use the sensed data for closing the feedback loop. Finally, a stimulation circuitry is required to effectively control a light source to deliver light based stimulation according to the feedback signal. Thus, the backbone to a functioning closed loop optogenetic stimulation device is a well-built electronic circuitry for sensing and processing of brain signals, running efficient signal processing and control algorithm, and delivering timed light stimulations. This paper presents a review of electronic and software concepts and components used in recent closed-loop optogenetic devices based on neuro-electrophysiological reading and an outlook on the future design possibilities with the aim of providing a compact and easy reference for developing closed loop optogenetic brain stimulation devices.

An Improved Digitizing Interface Circuit for Wide-Range Current-Output Sensors

A current digitizer, suitable for interfacing with a wide-range current-output sensor (COS) is proposed. The circuit features a transimpedance amplifier with a programmable-gain attenuating amplifier in its feedback which mimics the high-valued resistance required for a wide-range low-current to voltage conversion. The proposed scheme offers a fast response and is immune to switch resistances in the feedback circuit. This low-cost circuit uses a unipolar analog to digital converter (ADC) to sense bidirectional currents with reduced ADC quantization noise and offset error. A mathematical model of the scheme with error analysis is presented. The performance of the digitizing interface was established using simulations as well as experiments on a hardware prototype. The results show that the developed interface works well over the current range of 500 pA to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5 ~\mu \text{A}$ </tex-math></inline-formula> (dynamic range of 104) with nonlinearity (N. L.) less than 1.2%.

Direct Interface Circuit for Capacitive Sensors Affected by Parasitic Series Resistances

This article presents a novel circuit to directly interface a capacitive sensor affected by parasitic series resistances to a digital processor (DP). The presence of such resistances distorts the estimation of the capacitance to be measured. Current measurement procedures for these sensors, such as impedance-frequency characteristics, are complex and require significant hardware resources, power consumption, and time. To eliminate these drawbacks, a new circuit based on the so-called direct interface circuits (DICs) is introduced, which performs the digital reading of the sensors taking advantage of the presence of DPs in many applications. The hardware requirements in the new design are minimal: just two resistors and an operational amplifier in addition to the DP. The circuit requires only two time measurements to estimate sensor capacitance. These are obtained during a single capacitor charging-discharging process, simultaneously reducing power consumption and measurement time. The circuit has been implemented using a field-programmable gate array (FPGA), as the DP, in a general-purpose board to evaluate its performance. Although it is not an application-specific design, the circuit shows a maximum systematic error of 0.37% for capacitances in the 100 pF–96 nF range with parasitic series resistances up to 1200 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> . The maximum measurement time for this range is just 4.5 ms.

An epidermal electronic system for physiological information acquisition, processing, and storage with an integrated flash memory array.

Epidermal electronic systems that simultaneously provide physiological information acquisition, processing, and storage are in high demand for health care/clinical applications. However, these system-level demonstrations using flexible devices are still challenging because of obstacles in device performance, functional module construction, or integration scale. Here, on the basis of carbon nanotubes, we present an epidermal system that incorporates flexible sensors, sensor interface circuits, and an integrated flash memory array to collect physiological information from the human body surface; amplify weak biosignals by high-performance differential amplifiers (voltage gain of 27 decibels, common-mode rejection ratio of >43 decibels, and gain bandwidth product of >22 kilohertz); and store the processed information in the memory array with performance on par with industrial standards (retention time of 108 seconds, program/erase voltages of ±2 volts, and endurance of 106 cycles). The results shed light on the great application potential of epidermal electronic systems in personalized diagnostic and physiological monitoring.

A robust and flexible pulse wave sensory array enabling real-time non-invasive blood pressure monitoring

Chronical cardiovascular decreases such as hypertension requires real-time and continuous monitoring of blood pressures (BPs). Pulse wave that contains critical and ample information on cardiovascular dynamics is a direct vital sign to extract BP and therefore an epidermal wearable device enabling real-time acquisition of pulse waves becomes necessary. In this work, we propose and study a flexible pulse wave sensory array aiming for real-time wearable pulse wave acquisition with robustness. A piezoelectric sensor together with a thin-film transistor-based sensor interface circuit is used to detect multiple pulse waveforms at the location of radial artery, which are input to a convolutional neural network for a deep-learning BP estimation model training. The estimated BPs are assessed by a correlation study with the BPs measured by conventional sphygmomanometers. Our study shows a reasonable accuracy of mean deviation and standard deviation of 2.84 ± 7.53 mmHg for systolic BP and 0.88 ± 7.06 mmHg for diastolic BP.

A low power-integrated temperature sensor interface circuit

This paper constructs and simulates the interface circuit of a temperature sensor based on SMIC 0.18 [Formula: see text]m CMOS. The simulation results show that when the power supply voltage is 1.8 V, the chopper op-amp gain is 89.44 dB, the low-frequency noise is 71.83 nV/Hz,[Formula: see text] and the temperature coefficient of the core temperature sensitive circuit is 1.7808 mV/[Formula: see text]C. The sampling rate of 10-bit SAR ADC was 10 kS/s, effective bit was 9.0119, SNR was 59.3256 dB, SFDR was 68.7091 dB, and THD was −62.5859 dB. The measurement range of temperature sensor interface circuit is −50[Formula: see text]C[Formula: see text]C, the relative temperature measurement error is ±0.47[Formula: see text]C, the resolution is 0.2[Formula: see text]C/LSB, and the overall average power consumption is 434.9 [Formula: see text]W.

Calibration-Less Direct Inductor-to-Microcontroller Interface

A sensor-to-microcontroller interface circuit for inductive sensors that does not require a calibration inductor is presented. Three digital ports of a microcontroller, two transistors, and an embedded timer were used to measure the charging times of the inductor through forward- and backward-flow currents using two different initial conditions. The difference between the charging times was used to estimate the sensor inductance accurately without the uncertainty due to the tolerance of threshold voltage of the input port, which delimits these time length measurements. Experimental results show that a conventional low-power microcontroller with an embedded 16 MHz clock and 22 Ω charge resistance can be used to achieve 2 μH resolution and a systematic error below 2% for a measuring range from 100 μH to 10 mH. The advantages of the proposed technique include the reduction of cost and space as well as avoiding complex calibration processes caused by the temperature drift of the reference inductors.

A Passive, Skin-Attachable Multi-Sensing Patch Based on Semi-Liquid Alloy Ni-GaIn for Wireless Epidermal Signal Monitoring and Body Motion Capturing

Wearable integrated systems that rely on liquid metal commonly require an extremely complicated, high-cost fabrication process, while lacking multiple sensing functions without conductive wires connected to external electronic systems. A multi-sensing wearable patch independent from sophisticated manufacturing method and excessive use of wires has yet to be developed. Herein, we introduce a wireless, battery-free, and skin-attachable patch with multiple sensing capacities, utilizing a low-budget, less time-consuming and design-customizable fabrication method. In an effort to achieve our goal, the general sensing system architecture is promoted, which consists of a semi-liquid alloy Ni-GaIn based strain sensor and a co-designed near-field-communication (NFC) tag integrating thermistor, photoresistor, as well as sensor interface circuits, enabling energy-autonomous power supply and wireless data transmission. In human volunteers, the patch was mounted on the skin surface to demonstrate real-time temperature and light intensity signal monitoring. Further evaluation of body motion capturing involved finger bending and swallowing, demonstrating the feasibility of practical applications in different scenarios. Continuous and simultaneous multi-type signal sensing using the wearable patch should enrich the dimensions of measurements of body response to daily activities, unveiling the potential for remote human health monitoring, advanced human–machine interfaces, and other applications of interest.

A 0.4 V, 19 pW subthreshold voltage reference generator using separate line sensitivity and temperature coefficient correction stages

Sensor nodes and IoT systems require blocks that not only consume low power but also have good accuracy. Voltage reference generators are also considered important building blocks in sensor interface circuits. This paper presents a solution to increase the accuracy of low power subthreshold voltage generators by lowering the circuit sensitivity to temperature and supply voltage variations. The enhancement is achieved by using two separate stages for temperature coefficient (TC) and line sensitivity (LS) correction. A 0.18 µm standard CMOS process has been used for the proposed structure. The effects of parameter variations in the fabrication process are investigated using post-layout simulation and Monte Carlo analysis. In the supply voltage of 0.4–2 V, an LS of 143.8 ppm/V is obtained. In typical corner conditions, the achieved TC is 7.45 ppm/°C over the temperature range of 0–80 °C. Due to process changes, and mainly affected by threshold voltage variations, the average TC can change to 39.2 ppm/°C. The minimum power consumption at 0 °C and at a supply voltage of 0.4 V is 3.25 pW while the power consumption increases to 2.84 nW in 80 °C and at the maximum supply voltage of 2 V.

A Dual-Mode Multifunctional Pulsed Radio-Frequency Stimulator for Trigeminal Neuralgia Relief and its Animal Model.

This work proposed a programmable pulsed radio-frequency (PRF) stimulator for trigeminal neuralgia (TN) relief on demand. The implantable stimulator is a miniaturized micro-system which integrates a wireless interface circuit, a sensor interface circuit, a PRF pattern generation circuit and a logic controller. The multifunctional stimulator capable of delivering current/voltage stimulation provides the choice of the biphasic sinusoidal, square and patterned waveform for PRF treatment researches. The external handheld device can wirelessly transmit the parameters of frequency, amplitude, pulse duration and repetition rate of the pulse train to the implanted stimulator. While stimulating, the temperature sensor can monitor the operating temperature. The feedback signal is transmitted in medical implanted communication system (MICS). The micro-system is fabricated in a 0.35 μm CMOS process with a chip size of 3.1 × 2.7 mm2. The fabricated chip was mounted on a 2.6 × 2.1 cm2 test board for studying the in vivo efficacy of pain relief by PRF. Animal studies of PRF stimulation and commonly-used medication for trigeminal neuralgia are also demonstrated and the presented results prove that PRF stimulation has greater effectiveness on trigeminal neuralgia relief comparing to the medication. The effectiveness period lasts at least 14 days. The results of neural recording show that the PRF stimulation of trigeminal ganglion (TG) attenuated neuron activities without being severely damaged. Pathology also revealed no lesion found on the stimulated area.

Design and analysis of a waterproof capacitive touch key sensor interface circuit

Traditional mechanical keys are gradually replaced with touch keys. Capacitive touch keys have advantages in achieving higher sensitivity with a longer service life and lower cost. Hence, the capacitive touch key technology is widely used in consumer electronic products. In use of household electric appliances, such as electric kettle, induction cooker and exhaust hood, sometimes the water vapor would condense into visible moisture or even the water would splash out of the pot when overheated, which may lead to a falsely trigger of touch key. So, waterproof becomes a big challenge in household electric appliances. This paper analyzes how water affects capacitive touch key and proposes a waterproof capacitive touch key sensor interface circuit to overcome the challenge. Sensing of touch key capacitor would be influenced only when water covers more than two touch keys. Compensating channels working in certain strategy are used to decrease the influence of water. For the same water capacitor, the bigger threshold voltage, the bigger change of the counting number. A much smaller threshold voltage is better to further weak the effect of water. The circuit is implemented in a standard 110 nm CMOS process. The measured results show that the touch Signal to Noise and Water Disturb Ration (SNWDR) is 20.7 dB which proves that the proposed waterproof capacitive touch key sensor interface circuit is effective against water splash.

Intelligent Wireless Ultrasonic Device for Damage Detection of Metallic Structures

In today’s world, it is necessary to monitor structures for possible damages. A failure to monitor the structures properly can cause structural catastrophe. Many researchers have worked on the low-power ultrasonic device to monitor the structures. In this research, we present an intelligent ultrasonic device (IUD) to monitor and detect the damages on the structures. The device uses microcontroller, actuator interface circuit, sensor interface circuit and radio frequency (RF) modem. The microcontroller has in-built high-speed analog-to-digital converter (ADC), digital-to-analog converter (DAC) and floating-point unit for signal processing. The controller generates the tone-burst signal and sends it to actuator interface circuit. The actuator interface circuit conditions the received signal from the microcontroller and drives the Piezoelectric Transducer (PZT) actuator. The actuator generates an ultrasonic wave in the structure. The wave is then sensed by PZT sensors. The sensor interface circuit selects the signal from desired PZT sensor and sends it to the microcontroller for further processing. The microcontroller digitizes the signal and computes the damage index and only if the damage is severe, it will send data wirelessly to the nearby PC. To test the device, iron specimen was prepared, PZT actuator and PZT sensor was mounted on it. The artificial crack was then induced on the specimen. The ultrasonic wave was then collected from the structure. By analyzing the ultrasonic wave, the device successfully detected the induced crack in the structure. The future work will be to use GSM modem so that the device can be monitored in the real time from the remote location.