Patent ID: 6630834
Filing Date: 2003-10-07
Classification: G01P,G01R

Abstract:
An apparatus for measuring a change in capacitance in an object modeled as first and second capacitors connected in series between first and second terminals, wherein the capacitance of one of the first and second capacitors increases by a certain amount and that of the other decreases by the same amount when a perturbation is applied, the apparatus comprising:a first gain adjuster that adjusts the gain of an input signal and outputs the gain-adjusted input signal to the first terminal as a first modulating signal; a second gain adjuster that adjusts the gain of an inverted input signal and outputs the gain-adjusted inverted input signal to the second terminal as a second modulating signal; an amplifier that amplifies a modulated signal output from a junction between the first and second capacitors and outputs the amplified result; a demodulator that demodulates the amplified result received from the amplifier in response to a control signal and outputs the demodulated result; a controller that generates the control signal per unit period of the input signal and outputs the generated control signal to the demodulator; and a change measuring unit that measures the change in capacitance from the demodulated result received from the demodulator.