Interface Circuit Research Articles

Acoustic Energy Harvester by Electromagnetic Mechanisms and Helmholtz Resonator

In order to harvest the acoustic energy in the environment, an electromagnetic acoutic energy harvest system is proposed based on Helmholtz resonator, coil, permanent magnet and interface circuit. When the sound wave is injected into the resonator, it causes the upper surface permanent magnet to vibrate and outputs electrical energy from the coil. The resonant frequency of the resonator is simulated and analysed by finite element method, the interface circuit is simulated and analysed, the acousto-electric conversion principle is analysed theoretically. The output characteristics of the system under different frequencies and sound pressure levels are studied by experiments, and the output characteristics of the system after using the interface circuit are studied. The experimental results show that the system can harvest the acoustic energy of different frequencies, and the power generation effect is better when the acoustic frequency is near 98Hz and 140Hz, which is close to the first two resonant frequencies of the system. The output voltage and power of the system increase with the increase of the sound pressure level. When the sound pressure level is lower than 105dB, the output voltage and power of the system under the acoustic frequency of 95Hz is higher, and when the sound pressure level is greater than 105dB, the output voltage and power of 140Hz acoustic frequency is higher. After using the interface circuit, the maximum open-circuit voltage is 13.65V when the sound pressure level is 110dB and the frequency is 98Hz, and the maximum output power of the system can reach 0.625mW when the sound pressure level is 110dB and the frequency is 140Hz.

Research on SECE interface circuit for micro wind harvesting system with piezoelectric structure

Micro wind harvesting system with piezoelectric structure is an attractive method to power micro electric devices in outdoor field work. Interface circuit is one of the keys to improve the efficiency of harvested energy. A SECE interface circuit is design with microcontroller, which monitors the voltage and generates pulse signal. A simulation is performed in Multisim software to validate the proposed circuit. Results show that the maximum output power of classic interface circuit is 128.118μW at 110KΩ, and it increases to 390μW with proposed SECE interface circuit. It indicates that the efficiency of harvested energy is improved by 200%.

Method to Reduce Quantization Error in Direct Interface Circuits for Resistive Sensors

Reading resistive sensors and converting their information to digital values is a matter of great interest in practical applications. Direct Interface Circuits (DICs) perform this task efficiently through a resistance-to-time-to-digital conversion. The main benefit of this type of circuit is the simplicity of its design and the accuracy of the results. However, one of its drawbacks is that quantization errors in the measurements seriously compromise accuracy if the information is not converted using a high-frequency clock or with high capacitor values. To avoid this situation, this article presents a new type of DIC with the same passive elements as a classic DIC, but which uses a high value resistor in the final instant of the resistance-to-time conversion. The circuit has been implemented using a commercial FPGA with the capture module operating at different clock frequencies. The results show that relative errors in measuring resistors of up to $33~\Omega $ decrease to 1.56% when operating with a 12.5 MHz timer.

Guest Editorial Special Issue on Advanced Interface Circuits for Autonomous Smart Sensors

The quote by Lord Kelvin, “if you can’t measure it, you can’t improve it,” best captures the invaluable role of sensors in any system. It also implies that to improve the performance of a system one needs to employ advanced sensor solutions. The performance requirements vary from one application to another, but are always associated with accuracy, repeatability, reproducibility, range, power consumption, ease of installation, and maintenance. In the modern era of data science, machine learning, and artificial intelligence, there is an ever-increasing need for low-cost, high-performing sensors in high volumes.

Performance Verification of a Digital Interface Suitable for a Broad Class of Resistive Sensors

An improved digital interface circuit for resistive sensors is proposed in this paper. The circuit offers many positive features, such as (1) use of single-reference voltage in its architecture, (2) facility to tune/preset the sensor-excitation current, even for different values of resistive sensors, (3) minimal dependence on many circuit non-ideal parameters. The working of the circuit is mathematically described in this paper, followed by its extensive error evaluation. Detailed simulation and experimental studies are performed to verify the feasibility of the interface for three different types of sensors. These studies show that the circuit can efficiently be used in temperature-monitors, magnetometers, and displacement-sensing. The maximum experimental nonlinearity observed from all of these sensor configurations does not exceed 0.06 %. Then, the extensive studies are carried out by simulation as well as experimentation to show the effect of environmental temperature changes on the proposed circuit. Finally, the proposed circuit is compared with some of the recent resistive digital interfaces.

A Low-Power Time-to-Digital Converter for Sensor Interface Circuits

This brief proposes a new low-power time-to-digital converter (TDC). In contrast to the previous works that digitize each new input sample independent of the previous ones, the proposed structure obtains the digital code of the new sample based on the difference between the previous sample and the new one. Therefore, since the activity of the circuit is reduced, its power consumption is saved, especially for the applications that the variation of the input signal is usually much smaller than the signal range, such as sensor interface circuits. Based on the proposed structure, a 200 kS/s TDC circuit with a resolution of 3.2 ps is designed and simulated in a 65-nm CMOS technology. Post-layout simulation results show that the proposed structure achieves an effective number of bits (ENOB) of 7.52 bits at the cost of 10.1 μW power consumption. Moreover, the effective area occupied by the circuit is 110 μm × 130 μm.

A microcontroller-based interface circuit for non-linear resistive sensors

This article proposes a circuit based on a microcontroller unit (MCU) for the direct measurement and linearization of non-linear resistive sensors, such as thermistors. The measurement relies on an embedded digital timer and does not require (either embedded or external) operational amplifiers or an analog-to-digital converter, thus resulting in a low-cost, low-power design solution. The circuit includes a known resistor with a twofold function: it is a reference for circuit auto-calibration purposes, and it is in parallel with the non-linear resistive sensor for linearization purposes. A prototype is implemented with an 8-bit MCU (ATtiny 2313) applied to a commercial thermistor, and the results show a non-linearity error smaller than 1% full-scale span.

A discrete-time self-clocking complex electromechanical ƩΔM gyroscope with quadrature error cancellation

In this work, a new self-clocking electromechanical sigma-delta modulator (ƩΔM) quadrature error cancellation scheme for MEMS mode-matching gyroscopes is presented. The proposed techniques allow to decompose the gyroscope sense mode into in- and quadrature-phase signals and process it with two high-order sigma-delta control loops, achieving efficient noise shaping and error suppression. Furthermore, the system was designed with a self-clocking calibration scheme to provide temperature-independent turn-on bias output. Simulation results proved its robustness, a significant improvement for linearity and achieving over 80 dB attenuation of quadrature error. The hardware implementation comprising a discrete interface circuit and a wheel gyroscope was demonstrated. Measurement results validate the inherent loop quadrature cancellation scheme and demonstrate a sub-1°/hr bias instability (BI), with 5.5X and 3X improvement of BI and angle random walk (ARW) compared with a conventional single-loop ƩΔM gyroscope system. Combined with real-time self-clocking control, it yields an improvement of turn on bias error (1800s) and output linearity, achieving 1°/h and 0.021 %, respectively.

A measurement method for lossy capacitive relative humidity sensors based on a direct sensor-to-microcontroller interface circuit

A new time-domain measurement method for determining the capacitance and resistance values of lossy relative humidity capacitive sensors is presented. The method is based on a direct sensor-to-microcontroller interface for microcontrollers with internal analog comparators and timers. The interface circuit consists only of four reference resistors (two reference resistors if a microcontroller includes a voltage reference source), a given sensor and a microcontroller. A systematic error correction algorithm based on a correction dictionary and the M-multiple measurement approach are also proposed in the paper. Experimental investigations were carried out using a prototype device based on an 8-bit ATXmega32A4 microcontroller. The experimental research confirmed that the relative errors of measurement of capacitance introduced by the interface circuit are less than 0.71% (for capacitance values 100–286pF), and the relative errors of measurement of resistance are less than 0.74% (for resistance values 1–10MΩ).

Noise analysis and optimization of VCII-based SiPM interface circuit

Recently, second generation voltage conveyor (VCII)-based transimpedance amplifiers (TIAs) have begun to find their way in different applications, among which, silicon photomultipliers (SiPMs) interfacing circuitry. There are many advantages which make VCII-based TIAs attractive over conventional circuits: the intrinsic low impedance at VCII current input Y port is very helpful to mitigate the effect of high value sensor capacitance and provides fast response time; the achieved bandwidth is high and due to current mode operation; the circuits enjoy the low-voltage low-power features. As signal-to-noise ratio is a crucial parameter in SiPMs interface circuit applications, here we consider the noise specifications and optimization of VCII-based SiPM interface circuits. The noise model of VCII is introduced and equivalent noise of a VCII-based interface circuit is derived. Methods to optimize trade-offs existing between key parameters including power consumption, gain and noise performance are discussed. Simulation results are also provided showing a considerable reduction of two orders of magnitude in most of the noise performances when compared to the previous work while preserving other performance parameters.

System-level finite element analysis of piezoelectric energy harvesters with rectified interface circuits and experimental validation

The finite element method (FEM) has been widely used for numerical studies of piezoelectric energy harvesting (PEH) systems, through commercial finite element (FE) packages or specially developed FE formulations. As a convenient computational tool, FEM can deal with systems of high complexity and has evolved into a multiphasic solution to coupled problems in engineering. However, most of FE packages and formulations are limited to coupled-field simulations of PEH systems connected with a linear circuit. On the other hand, rectified circuits are a critical component in practical applications because electronic devices such as wireless sensor nodes and wearable electronics require a DC power supply. Based on the equivalent impedance analysis, this paper proposes a method to enable a coupled-field study of piezoelectric energy harvesters with the standard AC-DC interface circuit through an equivalent linear circuit. The proposed method enables FE packages and formulations to analyze, design, and optimize PEH harvesters at the system level, by either adding the capability of simulating rectified circuits, or reducing a nonlinear circuit interface simulation into a faster and more stable linear simulation that can be solved more conveniently. This equivalent linear circuit method was applied to a rectangular shaped bimorph beam harvester in ANSYS and validated experimentally. The results also match well with those obtained from a system-level analytical approach. As an application example, a comparison study was performed between the rectangular and triangular energy harvesters using FE packages and the proposed equivalent circuit, given the same natural frequency and material volume. In addition, the implementation of this method with FE formulations is briefly outlined and discussed.

A 70-μW 1.35-mm2 Wireless Sensor With 32 Channels of Resistive and Capacitive Sensors and Edge-Encoded PWM UWB Transceiver

This article presents a wireless multi-channel sensor interface circuit for emerging e-skin applications. The proposed interface circuit uses a CDMA-like sensing method to simultaneously record 16-channel resistive sensors and 16-channel capacitive sensors. The code-modulated multi-channel signals are conditioned and wirelessly transmitted through an edge-encoded pulsewidth-modulation ultra-wideband (PWM UWB) transmitter in the time domain. The PWM UWB transmitter eliminates the need for digitization on the sensor node, reducing the number of data to be sent. This improves the sensing and wireless transmission efficiency. With the proposed edge-encoding technique, the PWM UWB transmitter can recover the sensor data with SNR above 70 dB despite 20% data loss under a lossy environment. Fabricated in 130-nm technology, the wireless multi-channel sensor node occupies a die area of 1.35 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and consumes a power of 70 μW. It achieves an energy efficiency of 0.87 pJ/Conversion-step per channel.

Electrostatic Coupled Capacitance Sensor for Gas Solid Flow Measurement

Both electrostatic and capacitance sensing techniques have been increasingly attractive for gas solid flow measurement. Although independent flow monitoring can be achieved by either an electrostatic sensor or a capacitance sensor, the fusion of them could provide diversified flow information with simplified sensor structure when used for gas solid flow measurement. In this paper, a novel electrostatic coupled capacitance sensor is proposed for gas solid flow measurement, which could simultaneously act as an electrostatic sensor and a capacitance sensor and thus acquires electrostatic and capacitance information within the same sensing space. Through an in-depth theoretical analysis of the sensor principle based on a pair of concave electrodes, a corresponding interface circuit is designed for signal conversion and extraction. Experiments carried out on a single particle test rig and a belt-pulley rig verify that the electrostatic and capacitance signals can be simultaneously obtained from the proposed sensor through the designed interface circuit. Furthermore, a sensor prototype with a three-electrode configuration is designed to measure the particle velocity, concentration, mass flow rate and charge level on a gravity-fed solids flow rig, demonstrating the potential application of the developed electrostatic coupled capacitance sensor for the gas solid flow measurement.

Voice communication system according to the principle of mobile radio

This article discusses the problem of instant remote communication with people at a remote distance. The main task was the creation of an information system that provides confidential instant radio communication of all employees and partners of the company without additional devices. Use schemes and interface circuits were used. To justify the feasibility of developing a system, a comparative analysis of analogues was carried out and the distinctive advantages of the proposed method were highlighted. The article described the system requirements and the use of software for its implementation. In addition, the article discusses the principle of emergency SOS channel, with which you can call for help if you are in trouble. GPS capabilities and the principle of tracking the location of users are considered.

WITHDRAWN: Medical intelligent infusion monitoring system based on 5G network and FPGA

Abstract Medical infusions emphasize an approach to a distributed patient-centric approach, following a rapid transition from traditional hospitals and professionals. Several technological advances have provided medical assistance from long distances to facilitate this rapid transformation of medical verticality. Continuous medical infusion intelligent monitoring system improves people's lifestyle. These systems collect vehicle body signals via biomedical sensors and various collection systems to provide information about the patient's health. Multiple tasks are accomplished with the same interface, buffering and compression FPGA (Field Programmable Gate Array) devices. Capacitor interface circuits are used for medical infusion intelligence, which is based on the principle of capacitor frequency-voltage conversion. However, to achieve the highest monitoring quality, the patient's health level needs to be analyzed. In this article, patients with continuous infusion health monitoring can use 5 G technology and propose a system through it. The proposed system includes wearable sensors and devices, smartphones, and database systems that maintain data for all patients. The intelligent injection monitoring screen is displayed graphically after dripping the information obtained by observation and gadget injection. When the temperature sensor value reaches the threshold, the fluid flow is stopped immediately without any airflow in the patient's veins when the control valve is closed. The medical infusion data is compressed to avoid sending repeated values of any of the targets to further reduce power consumption.

A 0.39–3.56-μW Wide-Dynamic-Range Universal Multi-Sensor Interface Circuit

This paper presents an ultra-low-power, widedynamic-range interface circuit for capacitive and resistive sensors. The circuit is implemented as a switched-capacitor circuit using programmable capacitors to achieve high configurability. The circuit was fabricated using a CMOS 0.18 μm process. Different types of capacitive and resistive sensors were measured using the interface to demonstrate its support for multi-sensor systems with an ultra-low-power budget. Experimental results show that the circuit is able to interface various sensors within the overall capacitance range of 0.6-550 pF and resistance range of 3.7-5100 kΩ, while consuming only 0.39-3.56 μW from a 1.2 V supply. A proximity, gesture, and touch-sensing system is also developed consisting of the designed interface circuit and a sensor element that is able to detect the displacement of an object up to 15 cm from the sensing electrodes consuming only 0.83 μW from a 1.2 V supply.

An efficient macro model for CMOS-MEMS thermal wind speed sensor

In this paper, we propose a thermal wind speed sensor Verilog-A model with thermal-fluid-electric hybrid characteristics. Because the structure of the thermal wind sensor and the interface circuit chip are designed separately, which cannot effectively carry out MEMS-IC (integrated circuit) co-simulation, the overall performance of the sensor and interface circuit chip is prone to large deviation. At the same time, the separation of MEMS structure and IC design process leads to long product development cycle and high cost. This paper proposes an improved simulation model by analyzing the behavior characteristics of the thermal wind speed sensor. The simulation model consists of 11 thermistors, 3 capacitors, a voltage-controlled voltage source, and a voltage-controlled current source. The Taylor series expansion of the differential equation of heat conduction is carried out, and then the thermistor and capacitor networks are established according to the corresponding relationship between the thermal parameters and the electrical parameters, including the thermal conduction unit, the convection unit and the heat capacity in the chip. The model fully considers the effects of various physical effects and parasitic effects, and is implemented using the hardware description language Verilog-A. The sensor and interface circuit can be simulated simultaneously to optimize the circuit design. It is beneficial to the integration of sensors and interface circuit, reducing the number of tape-outs, increasing the success rate, and reducing costs. The consistency between the simulation results and the experimental curves verified the correctness of the macro model. The behavior characteristics of constant power (CP) and constant temperature heating were described. In CP mode, the output voltage error is less than ± 6.5%, the chip temperature error is less than 4.0%. The presented modeling approach can be the basis for the development of complete MEMS-IC design technology library of thermal wind speed sensor, aiming at optimum designs of integrated thermal wind speed sensor.

Design and Implementation of Dynamic FPAA Based Interface Circuit for Thin Film Lead-Free Piezoelectric Sensors

Design and Implementation of Dynamic FPAA Based Interface Circuit for Thin Film Lead-Free Piezoelectric Sensors

Time-Based Sensor Interface for Dopamine Detection

This paper describes the design of an integrated sensor interface for dopamine detection. The sensor interface circuit fabricated in 65 nm CMOS technology utilizes a time-based analog-to-digital conversion circuit built around a ring oscillator. The circuit supports a wide input current range of $\pm 1.2~\mu \text{A}$ and sampling rate of 1 - 20 kHz, enabling sub-second detection of neurochemicals within the supported current range. Measured results with physiologically relevant dopamine concentration of 500 nM demonstrate the ability of the sensor interface circuit to detect oxidation and reduction current peaks, which provides information about the release times and redox potentials of the neurochemical. This chemical information is essential in neurostimulation treatment of neurological and neurodegenerative diseases.

A Capacitive Pressure Sensor Interface IC with Wireless Power and Data Transfer.

This paper presents a capacitive pressure sensor interface circuit design in 180 nm XH018 CMOS technology for an implantable capacitive pressure sensor, which has a wireless power supply and wireless data transfer function. It integrates full-bridge rectifiers, shorting control switches, low-dropout regulators, bandgap references, analog front end, single slope analog to digital converter (ADC), I2C, and an RC oscillator. The low-dropout regulators regulate the wireless power supply coming from the rectifier and provide a stable and accurate 1.8 V DC voltage to other blocks. The capacitance of the pressure sensor is sampled to a discrete voltage by the analog front end. The single slope ADC converts the discrete voltage into 11 bits of digital data, which is then converted into 1 kbps serial data out by the I2C block. The “1” of serial data is modulated to a 500 kHz digital signal that is used to control the shorting switch for wireless data transfer via inductive back scatter. This capacitive pressure sensor interface IC has a resolution of 0.98 mmHg (1.4 fF), average total power consumption of 7.8 mW, and ±3.2% accuracy at the worst case under a −20 to 80 °C temperature range, which improves to ±0.86% when operated between 20 and 60 °C.