A novel low-cost capacitive-sensor interface

Abstract
This paper describes the design of a new capacitive sensor interface. The interface is based on the use of a novel type of oscillator whose frequency is insensitive to low- and high- frequency interfering signals by the application of a third order high-pass filter and special dither techniques. The fully integrated 0.7 pm CMOS circuit shows an inaccuracy of less than 100 aF with respect to a 2 pF reference capacitor over a -30" to +70° C temperature range. The applied measurement concept guarantees high stability, high accuracy and a negligible influence of parasitic capacitances without the need for calibration.

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