Patent ID: 7323886
Filing Date: 2008-01-29
Classification: G01R,H03F,H03K

Abstract:
1. An apparatus for detecting relative changes in capacitances of at least one first capacitor and at least one second capacitor, each of the at least one first capacitor and the at least one second capacitor having a first end and a second end, the apparatus comprising: at least one power source operative to produce at least one periodic output signal at at least one corresponding power source output; electrical circuitry including at least one operational amplifier and at least one difference amplifier, the electrical circuitry being coupled to the first ends of the at least one first capacitor and the at least one second capacitor, the second ends of the at least one first capacitor and the at least one second capacitor being electrically connected at the same time to a common ground, wherein the at least one power source output is operative to charge the at least one first capacitor and the at least one second capacitor, wherein the at least one operational amplifier is configured to employ negative feedback to maintain the first ends of the at least one first capacitor and the at least one second capacitor at substantially equal voltage potentials with respect to the common ground while the at least one first capacitor and the at least one second capacitor are being charged responsive to the at least one power source output, wherein the at least one difference amplifier is operative to provide at least one electrical signal, and wherein a substantially linear relationship exists between the at least one electrical signal and a specified arithmetic function involving one of a ratio of the capacitances of the at least one first capacitor and the at least one second capacitor and a difference between the capacitance of the at least one first capacitor multiplied by a first constant factor and the capacitance of the at least one second capacitor multiplied by a second constant factor.