Importance

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Abstract

A pair of sensing capacitors, each having a capacitance C.sub.1 and C.sub.2 respectively, based on a process variable, are coupled to a bridge node which is coupled to a summing node. A reference capacitor, coupled to the summing node, has a capacitance C.sub.REF greater than an expected maximum difference between the capacitances of the pair of sensing capacitors. Switches selectively couple the sensing capacitors and the reference capacitor to at least first and second voltages to derive charges representative of C.sub.1 -C.sub.2 and C.sub.REF. In one embodiment the sensing capacitors are operated to charge and discharge during respective first and second phases of first cycles and the reference capacitor is operated to charge and discharge during respective first and second phases of second cycles. In another embodiment, the reference capacitor is operated to charge and discharge during alternate phases of the first and second cycles and the sensing capacitors are operated to charge and discharge during respective first and second phases of all cycles.

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First Claim