Circuit for measuring capacitance
First Claim
1. A circuit for measuring the capacitance of a circuit element, comprising a reference capacitor, a switching circuit for cyclically charging and discharging the circuit element and the reference capacitor at the same frequency from a common voltage source, the charging of the circuit element being synchronized with either the charging or the discharging of the reference capacitor, and means for comparing currents of the circuit element and the reference capacitor to provide a measurement of the difference between the capacitances of the circuit element and the reference capacitor, wherein the comparing means comprises a reservoir capacitor circuit which is cyclically connected directly to the circuit element and the reference capacitor by the switching circuit so as to receive said currents of the circuit element and the reference capacitor, feedback circuit means for maintaining the charge stored by said reservoir capacitor circuit substantially constant so that the current supplied by the feedback circuit means to the reservoir capacitor circuit balances the said currents of the circuit element and the reference capacitor, and means for monitoring the operation of the feedback circuit means to provide said measurement.
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Accused Products
Abstract
A circuit and method for measuring the capacitance of a circuit element. A reference capacitor, a voltage source, and a switching circuit are arranged such that the circuit element and the reference capacitor are alternately charged and discharged from the voltage source at the same frequency, the charging of the circuit element being synchronized with either the charging or the discharging of the reference capacitor. Currents of the circuit element and the reference capacitor, for example the discharge currents, are supplied to a reservoir capacitor circuit and compared to provide a measure of the difference between the capacitances of the circuit element and the reference capacitor. The comparison is made by monitoring the feedback current necessary to maintain the charge of the reservoir capacitor circuit substantially constant.
98 Citations
8 Claims
- 1. A circuit for measuring the capacitance of a circuit element, comprising a reference capacitor, a switching circuit for cyclically charging and discharging the circuit element and the reference capacitor at the same frequency from a common voltage source, the charging of the circuit element being synchronized with either the charging or the discharging of the reference capacitor, and means for comparing currents of the circuit element and the reference capacitor to provide a measurement of the difference between the capacitances of the circuit element and the reference capacitor, wherein the comparing means comprises a reservoir capacitor circuit which is cyclically connected directly to the circuit element and the reference capacitor by the switching circuit so as to receive said currents of the circuit element and the reference capacitor, feedback circuit means for maintaining the charge stored by said reservoir capacitor circuit substantially constant so that the current supplied by the feedback circuit means to the reservoir capacitor circuit balances the said currents of the circuit element and the reference capacitor, and means for monitoring the operation of the feedback circuit means to provide said measurement.
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8. A method for measuring the capacitance of a circuit element, wherein the circuit element and a reference capacitor are alternately charged and discharged at the same frequency from a common voltage source, the charging of the circuit element being synchronized with either the charging or the discharging of the reference capacitor, and currents of the circuit element and the reference capacitor are compared to provide a measure of the difference between the capacitances of the circuit element and the reference capacitor, wherein the circuit element and the reference capacitor are cyclically connected directly to a reservoir capacitor circuit so that said currents are received by the reservoir capacitor circuit, the charge stored by said reservoir capacitor circuit is maintained substantially constant by a feedback circuit means so that the current supplied by the feedback circuit means to the reservoir capacitor circuit balances the said currents of the circuit element and the reference capacitor, and the operation of the feedback circuit means is monitored to provide said measurement.
Specification