Parasitic capacitance cancellation in capacitive measurement applications
First Claim
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1. An integrated circuit for measuring capacitance of a sense plate structure, said integrated circuit comprising:
- a reference capacitor;
means for periodically applying a fixed charging voltage to said sense plate structure;
a charge transfer circuit for periodically charging said reference capacitor, said charge transfer circuit including at least one current mirror structure having an input for receiving a current from said sense plate structure and generating an output current that is a scaled version of said input current;
a switch for periodically connecting said sense plate structure to said current mirror input, wherein the periodic charging of the sense plate structure, charging said reference capacitor and connecting the sense plate to the current mirror input form a charge transfer cycle; and
means for determining the capacitance of said sense plate based on the accumulated amount of charge in the reference capacitor.
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Abstract
An integrated circuit for compensating for parasitic capacitance in a capacitive measuring apparatus wherein a capacitance measurement is done by repeatedly transferring charge from a capacitor to be measured to a reference capacitor.
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Citations
13 Claims
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1. An integrated circuit for measuring capacitance of a sense plate structure, said integrated circuit comprising:
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a reference capacitor; means for periodically applying a fixed charging voltage to said sense plate structure; a charge transfer circuit for periodically charging said reference capacitor, said charge transfer circuit including at least one current mirror structure having an input for receiving a current from said sense plate structure and generating an output current that is a scaled version of said input current; a switch for periodically connecting said sense plate structure to said current mirror input, wherein the periodic charging of the sense plate structure, charging said reference capacitor and connecting the sense plate to the current mirror input form a charge transfer cycle; and means for determining the capacitance of said sense plate based on the accumulated amount of charge in the reference capacitor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of adjusting the number of charge transfer cycles in a capacitive measurement circuit, wherein said circuit includes a sense plate structure, an integrated circuit with an on-chip reference capacitor, one or more current mirror structures contained by said integrated circuit, said current mirror structures used to scale charge effectively flowing from said sense plate structure to said reference capacitor, and wherein said method comprises the steps of:
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periodically charging said sense plate structure with a known voltage; periodically transferring charge from said sense plate structure to said reference capacitor; utilizing said one or more current mirror structures to scale the amount of charge flowing from the sense plate structure to the reference capacitor; and adjusting the number of charge transfer cycles through a selection of ratios for said current mirror structures. - View Dependent Claims (11)
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12. A method of adjusting the amount of charge removed during compensation for parasitic capacitance in a capacitive measurement circuit, wherein said circuit includes a sense plate structure, an integrated circuit with an on-chip reference capacitor and one or more current mirror structures used to scale charge which is removed from said reference capacitor, and wherein said method comprises the steps of:
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periodically charging said sense plate structure with a known voltage; periodically transferring charge from said sense plate structure to said reference capacitor; periodically removing an amount of charge from said reference capacitor; utilizing said one or more current mirror structures to scale said amount of charge removed from said reference capacitor; and adjusting the amount of charge removed through a selection of ratios for said current mirror structures. - View Dependent Claims (13)
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Specification