A simple interface circuit for digital readout of lossy capacitive sensors

Direct Interface Circuits (DICs) allow straightforward digital reading from a range of sensors. Their architecture consists of a few passive components that help a digital processor (DP) perform a series of charge and discharge processes that provide time measurements to determine the sensor's resistive, capacitive, or inductive magnitudes. This article presents a new DIC that only requires two resistors for the digital readout of a group of sensors with a wide range of applications, namely lossy capacitive sensors. The DP does not need any analog element in its architecture, and the arithmetic operations involved are simple additions and multiplications. Apart from its simplicity, the new circuit brings significant improvements compared to other DICs proposed in the literature for the same type of sensors. Thus, the systematic errors in the capacitance estimates are only 0.30% for a wider range (100 pF − 95.92 nF), and the measurement time is 34% shorter.Funding for open access charge: Universidad de Málaga / CBU

A Closed-loop capacitance to pulse-width converter for single element capacitive sensors

A novel closed-loop capacitance-to-pulse width converter (CPC) suitable for single element capacitive sensors that use sinusoidal excitation is presented in this paper. Its operation is realized using a new configuration based on a simple, yet effective, auto-balancing scheme. The hardware prototype of the proposed CPC is relatively less complex to implement than those presented so far in the literature. It provides a quasi-digital output at a high update rate. Additionally, the output is insensitive to parasitic capacitances of the sensor. The output possesses high linearity, with respect to change in the sensor capacitance, ranging +/-5 pF, with a nominal capacitance as high as 200 pF. It exhibits a maximum non-linearity error of 0.061%FS. The output of the prototype has a resolution of 13.31 bits. Also, its response time for a step-change in the sensor capacitance is about 13 ms. This sophisticated and inexpensive closed-loop CPC is a perfect fit as an interfacing circuit for single element capacitive sensors.Peer ReviewedPostprint (author's final draft

Analysis of a direct microcontroller interface for capacitively coupled resistive sensors

© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. DOI:10.1109/TIM.2020.3034969A novel approach to directly interface a capacitively coupled resistive sensor to a microcontroller is presented in this article. The existing measurement schemes for such sensors are complex. In addition, the coupling capacitance often also holds important data. The proposed simple measurement system, for such series RC sensors, is capable of measuring both the resistance and the coupling capacitance. A detailed analysis on the effect of the nonidealities on the resistance measurement showed that it is independent of the accuracy of the charging capacitor, supply voltage, and preset threshold voltagePostprint (published version

An ECG-on-Chip with QRS Detection & Lossless Compression for Low Power Wireless Sensors

IEEE Transactions on Circuits and Systems II: Express BriefsPP991-

Development of impedance spectroscopy based in-situ, self-calibrating, on-board wireless sensor with inbuilt metamaterial inspired small antenna for constituent detection in multi-phase mixtures like soil

Real time and accurate measurement of sub-surface soil moisture and nutrients is critical for agricultural and environmental studies. This work presents a novel on-board solution for a robust, accurate and self-calibrating soil moisture and nutrient sensor with inbuilt wireless transmission and reception capability that makes it ideally suited to act as a node in a network spread over a large area. The sensor works on the principle of soil impedance measurement by comparing the amplitude and phase of signals incident on and reflected from the soil in proximity of the sensor. The permittivity of the soil dielectric mixture which is calculated from these impedance measurements is used as input parameter to the dielectric mixing models which are used to estimate the ionic concentration in soil. The inbuilt wireless transceiver system is connected to a specially designed metamaterial inspired small antenna in order to reduce the sensor size while keeping the path losses to a minimum by using a low frequency. This composite right-left handed (CRLH) antenna for wireless transmission at 433 MHz doubles up as an underground, sensing element (external capacitor) and integrates with the on-board sensor for soil moisture and nutrient determination. The input impedance of the CRLH sensor, surrounded by the soil containing moisture and nutrient and other ions, is measured at multiple frequencies. It is shown that the change in moisture and ioinic-concentration can be successfully detected using the sensor. The inbuilt self-calibrating mechanism makes the sensor reliable at different environmental conditions and also useful for remote, underground and hand-held applications. A multi-power mode transceiver system has been designed to support the implementation of an energy efficient medium-access-control

New Electronic Interface Circuits for Humidity Measurement Based on the Current Processing Technique

The paper describes a new electronic conditioning circuit based on the current-processing technique for accurate and reliable humidity measurement, without post-processing requirements. Pseudobrookite nanocrystalline (Fe2TiO5) thick film was used as capacitive humidity transducer in the proposed design. The interface integrated circuit was realized in TSMC 0.18 mu m CMOS technology, but commercial devices were used for practical realization. The sensing principle of the sensor was obtained by converting the information on environment humidity into a frequency variable square-wave electric current signal. The proposed solution features high linearity, insensitivity to temperature, as well as low power consumption. The sensor has a linear function with relative humidity in the range of Relative Humidity (RH) 30-90 %, error below 1.5 %, and sensitivity 8.3 x 10(14) Hz/F evaluated over the full range of changes. A fast recovery without the need of any refreshing methods was observed with a change in RH. The total power dissipation of readout circuitry was 1 mW

ACME: An energy-efficient approximate bus encoding for I2C

In ultra low power systems with many peripherals, off-chip serial interconnects contribute significantly to the total energy budget. Leveraging the error-resilience characteristics of many embedded applications, the approximate computing paradigm has been applied to serial bus encodings to reduce interconnect consumption. However, the power model considered in previous works was purely capacitive. Accordingly, the objective of these approximate encodings was simply to reduce the transition count. While this works well for most bus standards, one notable exception is represented by I 2 C, whose open-drain physical connection makes the static energy consumed by logic-0 values on the bus extremely relevant. In this work, we propose ACME, the first approximate serial bus encoding targeting specifically I 2 C connections. With a simple encoding/decoding scheme, ACME concurrently reduces both the static and dynamic energy on the bus by maximizing the number of logic-1 values in codewords, while simultaneously reducing transitions. Using an accurate bus model and realistic capacitance and resistance values selected according to the I 2 C standard, we show that our encoding outperforms state-of-the-art solutions and reduces the total energy consumption on the bus by 57% on average, with an error smaller than 0.1%

Rayleigh-Bloch waves in CMUT arrays

Cataloged from PDF version of article.Using the small-signal electrical equivalent circuit of a capacitive micromachined ultrasonic transducer (CMUT) cell, along with the self and mutual radiation impedances of such cells, we present a computationally efficient method to predict the frequency response of a large CMUT element or array. The simulations show spurious resonances, which may degrade the performance of the array. We show that these unwanted resonances are due to dispersive Rayleigh-Bloch waves excited on the CMUT surface-liquid interface. We derive the dispersion relation of these waves for the purpose of predicting the resonance frequencies. The waves form standing waves at frequencies where the reflections from the edges of the element or the array result in a Fabry-Pérot resonator. High-order resonances are eliminated by a small loss in the individual cells, but low-order resonances remain even in the presence of significant loss. These resonances are reduced to tolerable levels when CMUT cells are built from larger and thicker lates at the expense of reduced bandwidth. © 2014 IEEE