A New Capacitance-to-Digital Convertor Suitable for Human Proximity Sensing

Abhishek Ranjan, Boby George

Abstract

This paper presents a new, simple and efficient dual-slope Capacitance-to-Digital Converter (CDC) that gives digital values of capacitances in a π-model of a capacitive proximity sensor. This CDC is suitable for a capacitive proximity sensor with two electrodes. When a human approaches the electrodes, it forms three capacitances, i.e., between human body and first electrode, between body and second electrode and between body and ground. It can be represented in a T-model or in an equivalent π-model. Conventional signal conditioning methods can provide only a single output from this network. It will be very useful, in a proximity sensing point of view, if the signal conditioning circuit can capture changes in those three individual capacitances and provide corresponding outputs. Further it will also be useful, to store and process easily, if these outputs are obtained in digital form, directly. A novel dual-slope CDC that measures all the three values of the capacitances in a π-model and provides those three digital outputs has been developed and details are presented in this paper. Measuring all the three capacitance is advantageous because it can detect proximity as well as provides location of body in relation to sensor electrodes. A prototype CDC has been developed and tested. Results are promising.

Keywords

proximity sensing, capacitance to digital convertor, dual slope

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IMEKO TC

TC4 - Measurement of Electrical Quantities

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