US Patent 7235986 Capacitive position sensing system with resonant amplification

At least one exemplary embodiment of the present invention includes a capacitive sensing system, comprising a sensing conductor coupleable to a grounded target by a gap capacitance Cd, said grounded target separated from said sensing conductor by a gap having a width. The capacitive sensing system also comprises a circuit connected to said sensing conductor, an input signal having an input frequency fosc provided to said circuit through an input resistance Rd, an output signal of said circuit having an output voltage varying linearly with the width of the gap when the impedance of the gap capacitance 1/(2πfoscCd) approaches or exceeds the input resistance Rd.