A digital converter that directly translates variations in the capacitances of a differential-type capacitive sensor to a proportional digital value is described in this paper. A conventional dual-slope, analog-to-digital converter is suitably modified to obtain direct capacitance-to-digital conversion (CDC). Analysis of the proposed technique indicates that the effects of nonidealities and variations in circuit parameters on the performance of the CDC is either in the form of a gain error and/or an offset, both of which can be easily compensated. Simulation studies and experimental results obtained from a prototype built and tested prove the efficacy of the proposed scheme. © 2008 IEEE.

Varadarajan Jagadeesh Kumar

Department of Electrical Engineering

Amol Ravikant Shet

S. Kedarnath

Capacitance

Digital arithmetic

Digital to analog conversion

Frequency converters

Networks (circuits)

Sensor networks

Sensors

ANALOG-TO-DIGITAL CONVERTERS

CAPACITIVE SENSORS

CIRCUIT PARAMETERS

DIFFERENTIAL CAPACITIVE SENSOR

DIFFERENTIAL CAPACITIVE SENSORS

DIGITAL CONVERSIONS

DIGITAL CONVERTER

DIGITAL CONVERTERS

DIGITAL VALUES

DUAL-SLOPE TECHNIQUE

GAIN ERRORS

SENSOR SIGNAL CONDITIONING

Simulation studies

Analog to digital conversion

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Digital Converter for Differential Capacitive Sensors

IEEE Transactions on Instrumentation and Measurement

A capacitance-to-digital converter (CDC) designed to possess negligible sensitivity to non-ideal circuit parameters is presented in this paper. The scheme is based on switched capacitor integrating technique and the conversion process is such that the final output is fundamentally insensitive to leakage resistance and stray capacitance of the sensor, offset voltage and bias current of the opamp, delay, offset voltage, and bias current of the comparator, leakage current, delay, and charge injection of the switches employed, and so on. Such a characteristic is highly useful for precision measurement. The proposed CDC achieves it without any special compensating circuits, unlike some of the existing CDCs that partially meet the above feature. The performance of the CDC has been experimentally evaluated. Results show high insensitivity to the non-ideal circuit parameters. In addition, the worst case non-linearity error of the prototype CDC was found to be less than 0.1%, when tested for a range of 10 to 400 pF. © 2001-2012 IEEE.

IEEE Sensors Journal

A robust switched-capacitor CDC

A dual-slope capacitance-to-digital converter (CDC) that operates on the elements of a differential capacitive sensor and provides a digital output that is linearly proportional to the physical quantity being sensed by the sensor is presented and analyzed in this paper. The converter topology is so chosen that a linear digital output is obtained for not only a sensor possessing linear inputoutput characteristics but also a sensor possessing inverse characteristics. The digital output in the proposed converter is dependent only on, apart from the sensitivity of the sensor, a dc reference voltage. Hence, high accuracy and linearity are easily obtained by employing a precision dc reference. Since the proposed CDC is based on the popular dual-slope analog-to-digital converter structure, it possesses all the advantages (resolution, accuracy, and immunity to noise and component parameter variations) and limitations (requirement of auto-zero and low conversion speed) applicable to the dual-slope technique. A prototype built and tested for a typical differential capacitive sensor with a nominal capacitance value of 250 pF gave a worst-case error of less than 0.05%. © 2006 IEEE.

Analysis of the switched-capacitor dual-slope capacitance-to-digital converter

2006 IEEE Instrumentation and Measurement Technology Conference Proceedings

A relaxation-oscillator-based interface for high-accuracy ratiometric signal processing of differential-capacitance transducers

A low-cost, smart capacitive position sensor

An Integrating Analog-to-Digital Converter for Differential Transducers

Digital converter for differential capacitive sensors

Journal	IEEE Transactions on Instrumentation and Measurement
ISSN	00189456
Open Access	No