A novel low-cost capacitive-sensor interface

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 μm 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