A Capacitance-to-Digital Converter with Sinusoidal Excitation Suitable for Series RC Sensors

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International Journal on Smart Sensing and Intelligent Systems

Professor Subhas Chandra Mukhopadhyay

Exeley Inc. (New York)

Subject: Computational Science & Engineering , Engineering, Electrical & Electronic

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VOLUME 7 , ISSUE 5 (December 2014) > List of articles

Special issue ICST 2014

A Capacitance-to-Digital Converter with Sinusoidal Excitation Suitable for Series RC Sensors

Prashanth Vooka / Boby George

Keywords : Capacitance-to-digital converter; capacitive sensor; floating capacitive sensor; current source for capacitive sensors

Citation Information : International Journal on Smart Sensing and Intelligent Systems. Volume 7, Issue 5, Pages 1-5, DOI: https://doi.org/10.21307/ijssis-2019-091

License : (CC BY-NC-ND 4.0)

Published Online: 15-February-2020

ARTICLE

ABSTRACT

A new Capacitance-to-Digital Converter (CDC) applicable for series RC sensors that requires/prefers sinusoidal excitation is proposed in this paper. The CDC presented works based on a dual-slope technique and it gives a digital output as a function of unknown capacitance of a series RC sensor, i.e., a capacitive sensor with a capacitor and a resistor in series in its electrical equivalent circuit. Output of the CDC is not sensitive to the series resistor. The CDC is useful for grounded as well as floating capacitive sensors, which needs to be excited with a sine wave for best performance. Applications of such capacitive sensors include ice detection, sterility testing of packed food products, etc. A sinusoidal Howland current source can be used to excite a grounded capacitive sensor while a simple current source with a special stabilization scheme that suppresses the effect due to static errors of opamp has been developed for floating capacitive sensor and presented in this paper. A prototype of the proposed CDC for a floating capacitive sensor has been built and tested in the laboratory. Measurement results for the sensor capacitance showed a worst case error of 0.13% for a range of 100 pF, proving the efficacy of the proposed scheme.

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