A Supply-Voltage Driving Scheme for Grounded Capacitive Sensor Front-Ends
Marcelo Haberman, Enrique Mario Spinelli, Ferran Reverter
Abstract
In this article, a novel supply-voltage driving scheme for capacitive sensor front-ends is proposed to eliminate the parasitic capacitances effects. The suggested circuit is intended for remote sensors (and, hence, connected to the circuit through a shielded cable) with one electrode grounded and of low capacitance (in the 0-10 pF range). The effects of the parasitic capacitance of the cable are avoided using the active-shielding technique, whereas those of the amplifier input through a smart driving of the reference node of the amplifier supply voltage. Thanks to these techniques, the input-output characteristic shows, without applying any adjustment and/or calibration, an offset error lower than 3 fF. The non-linearity error is in the order of 0.01% of the full-scale span, which corresponds to 1 fF. Different operational amplifiers and different lengths (up to 15 meters) of the interconnecting cable are experimentally tested to demonstrate the feasibility of the circuit. In comparison with similar circuits recently suggested in the literature, the proposed circuit does not require any bulky component, such as a transformer, and consequently it is a lower cost solution and suitable to be integrated.