Koniyath Semeerali

Bio: Koniyath Semeerali is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Electronic circuit & Relaxation oscillator. The author has an hindex of 1, co-authored 1 publications receiving 22 citations.

A Resistive Sensor Readout Circuit With Intrinsic Insensitivity to Circuit Parameters and Its Evaluation

Abstract: A novel readout circuit for interfacing single element resistive sensors is presented in this paper. The proposed scheme is based on a new relaxation oscillator (RO). The RO, along with a timer counter provides a digital output proportional to the resistance of the sensor. The output characteristic of most of the existing readout circuits for resistive sensors suffers from gain, offset, and nonlinearity errors. The sources of errors include various nonideal circuit parameters and their drift. The output of the proposed readout circuit has a special feature that it is not a function of the circuit parameters such as: 1) offset voltages of the opamps and comparators; 2) bias currents of the opamps and comparators; 3) gain of various units employed; 4) ON-resistance of the switches; 5) value or mismatch in the magnitudes of the reference voltages employed; 6) delay of the switches and comparator; 7) leakage current of the switch; and 8) slew rate of the opamp. Such a scheme will be useful for high accuracy measurements, even when the parameters 1)–8) may vary or drift, due to variation in the measurement environment. A prototype of the proposed readout scheme has been developed in the laboratory and the performance has been evaluated under various conditions. The output was found to be linear with a worst-case nonlinearity of 0.05%. Test results from a prototype developed show that the proposed scheme possesses all the features, described above, as expected.

On the Identification of Electrical Equivalent Circuit Models Based on Noisy Measurements

Abstract: Real-time identification of electrical equivalent circuit models (ECMs) is a critical requirement in many practical systems, such as batteries and electric motors. Significant work has been done in the past developing different types of algorithms for system identification using reduced-order ECMs. However, little work was done in analyzing the theoretical performance bounds of these system identification approaches. Given that both voltage and current are measured with error, proper understanding of theoretical bounds will help in designing a system that is economical in cost and robust in performance. In this article, we analyze the performance of a linear recursive least squares (RLS) approach to ECM identification and show that the LS approach is both unbiased and efficient when the signal-to-noise ratio is high enough. However, we show that when the signal-to-noise ratio is low–resembling the case in many practical applications–the LS estimator becomes significantly biased. Consequently, we develop a parameter estimation approach based on the total LS method and show it to be asymptotically unbiased and efficient at practically low signal-to-noise ratio regions. Further, we develop a recursive implementation of the total least square algorithm and find it to be slow to converge; for this, we employ a Kalman filter to improve the convergence speed of the total LS method. The resulting total Kalman filter (TKF) is shown to be both unbiased and efficient in ECM identification. The performance of this filter is analyzed using real-world current profiles under fluctuating signal-to-noise ratios. Finally, the applicability of the algorithms and analysis in this article in identifying higher-order electrical ECMs is explained.

Microdroplet Based Organic Vapour Sensor on a Disposable GO-Chitosan Flexible Substrate

Abstract: With rising hazardous organic vapours in the environment, the detection of volatile organic vapour compounds (VOCs) is becoming important. To this end, this paper presents a conductive droplet-based disposable sensor. Unlike conventional sensors, the droplet system is easily replaceable and is capable of detecting multiple vapours based on surface tension gradient. The chemiresistive sensor presented here is fabricated on $2.5~\mu \text{m}$ thick ultra-flexible graphene oxide-chitosan (GOC) with Pt electrodes having $60~\mu \text{m}$ gap. The electrostatic interaction and strong hydrogen bonds between GO and polysaccharide groups in chitosan provide tunable hydrophobicity and stability to the droplet. With a conductive droplet of $\sim 10~\mu \text{L}$ of aq. NaCl as an active sensing material dispensed between the Pt electrodes, it was observed that the droplet showed 14-21% change in resistance in the presence of VOCs. A read-out circuit was also designed to get the data from the droplet sensor. The response time for the presented sensor (3-4 seconds) is significantly better than its solid-state sensor counterparts. With attractive features such as disposability, affordability and fast response the presented sensor will find applications in industrial environments, laboratories, health centres, and biomedical devices.

Simple and Efficient Relaxation-Oscillator-Based Digital Techniques for Resistive Sensors — Design and Performance Evaluation

Abstract: This article proposes simple relaxation-oscillator-based digital interfacing schemes for resistive sensors in single-element and quarter-bridge forms. The proposed interfaces, equipped with novel compensation techniques, render a direct-digital output proportional to sensor resistance. These interfaces offer many meritorious features, such as simplicity of design, nonrequirement of the reference voltage, lower execution time, and negligible influences from circuit nonidealities. The methodology of the interfaces and their design criteria and error analysis are described in this article. The first two interfaces are suitable for nonremote resistive sensors, while the third interface has been developed for remotely located resistive sensors. The functionality of the proposed interfaces has been verified using simulation as well as detailed experimental studies. The developed interfaces provide a linear direct-digital output, and the maximum experimental nonlinearity is merely 0.08%. Later, a representative sensor based on the giant magnetoresistance (GMR) phenomenon is selected, characterized, and tested with the developed interfaces. The complete instrumentation system is shown to act as a linear digital magnetometer. Finally, the performance of the developed interfaces is compared and shown to be better/comparable with respect to the existing works.

AN-Z2V: Autonulling-Based Multimode Signal Conditioning Circuit for R-C Sensors

Abstract: In this article, we propose an autonulling-based multimode impedance-to-voltage converter (AN-Z2V) signal conditioning circuit for resistive–capacitive (R-C) sensors. The proposed technique takes advantage of the reuse of the phase tracking and autonulling modules to extract the in-phase and quadrature components of the sensors. The circuit is designed for three sensing modes: 1) Mode-C for capacitive sensors with leakage resistor; 2) Mode-R for resistive sensors with parasitic shunt capacitor; and 3) Mode-Z for impedance R-C sensor. A novel autotuning quadrature phase generator circuit is designed and implemented for the generation of reference 90° phase-shifted signal for the leaky capacitive sensors. A prototype of the proposed circuit is fabricated and tested. Measurement results show that AN-Z2V provides the measurement range with low relative error compared with the reported systems. The system is tested for a range of 10–760 pF and 56 $\text{k}\Omega $ –6.5 $\text{M}\Omega $ for mode-C and mode-R, respectively. The accuracy of the proposed circuit is found to be ±0.11% and ±0.07% for mode-C and mode-R, respectively. The capacitance and resistance of the impedance R-C sensor are simultaneously measured in mode-Z for a range of 33–528 pF and 100 $\text{k}\Omega $ –7.8 $\text{M}\Omega $ , respectively.

Low-Frequency RFID Signal and Power Transfer Circuitry for Capacitive and Resistive Mixed Sensor Array

Abstract: This paper presents a contactless measurement system for a mixed array of resistive and capacitive sensors exploiting a low-frequency radio-frequency identification (RFID)-based approach. The system is composed of a reader unit which provides power to and exchanges measurement data with a battery-less sensor unit. The sensor unit is based on a transponder operating at 134.2 kHz and a microcontroller. The microcontroller sequentially measures the elements of the sensor array composed of n capacitive and m resistive sensors which share a common terminal. The adopted technique measures the charging time of a resistor–capacitor (RC) circuit, where the resistor or the capacitor can be either the sensing element or a reference component. With the proposed approach, the measured values of the resistive or capacitive elements of the sensor array are first-order independent from the supply voltage level. A prototype has been developed and experimentally tested with resistive elements in the range 400 kΩ–1.2 MΩ and capacitive elements in the range 200 pF–1.2 nF showing measurement resolution values of 1 kΩ and 5 pF, respectively. Operative distances up to 3 cm have been achieved, with readings taken faster than one element of the array per second.