Importance

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Abstract

A method and apparatus for measuring an unknown capacitance using a known reference capacitance, wherein a first electrode of the unknown capacitance is connected to ground. The apparatus includes a first device for precharging the unknown capacitance to a first predetermined potential; a second device for selectively charging a first electrode of the reference capacitance to the same potential as the second electrode of the unknown capacitance, without changing the potential on the second electrode of the unknown capacitance; a first switch for selectively electrically connecting the first electrode of the reference capacitance to the second electrode of the unknown capacitance; a third device for switching the potential on the second electrode of the reference capacitance between a first predetermined value and a second predetermined value; a comparator for comparing the potential on the second electrode of the unknown capacitance to a reference voltage; and a sequencer responsive to the output from the comparator and designed to control the second device, the first switch, and the third device, and for counting the number of times these devices are used. The number of times these devices are used in a particular measuring operation according to the present method, is indicative of the unknown capacitance.

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First Claim