CAPACITANCE MEASUREMENT SYSTEMS AND METHODS
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Abstract
A first capacitor and a second capacitor are charged until voltage at the second capacitor settles to a settling voltage. While charging, the first capacitor is alternately switched between a current source and ground. When the settling voltage is reached, charging of the first capacitor is halted. The second capacitor continues to be charged until voltage at the second capacitor reaches a reference voltage. The amount of time it takes for the settling voltage to reach the reference voltage corresponds to a measure of capacitance on the first capacitor.
29 Citations
46 Claims
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1-26. -26. (canceled)
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27. A system comprising:
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a current source coupled to a first node of a first capacitor and to a first node of a second capacitor, the current source configured to provide a charge on the first and second capacitors, wherein the charge placed on the first and second capacitors generates a voltage potential across the first and second capacitors; a switch network comprising a first switch configured to couple the current source and the first node of the first capacitor to the first node of the second capacitor and a second switch configured to couple the first node of the first capacitor to a second node of the second capacitor; and a voltage measurement circuit configured to measure the voltage potential across the first and second capacitors, wherein the second capacitor is coupled to the measurement circuit after the current source is configured and coupled to the first node of the first capacitor, and wherein the currently source is configured to provide a charge on the first capacitor according to a predetermined charge rate. - View Dependent Claims (28, 29, 30, 31, 32, 33, 34)
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35. A method for measuring a capacitive input comprising:
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configuring a current source to charge a first capacitor, wherein a first node of the first capacitor is the capacitive input and wherein the current source has an adjustable output; coupling the first capacitor and the current source to a multiplexor bus; coupling a second capacitor to the multiplexor bus; charging a first capacitor and a second capacitor until voltage at the second capacitor settles to a settling voltage, wherein during the charging the first capacitor is switched back and forth between a current source and ground; when the settling voltage is reached, halting charging of the first capacitor while continuing to charge the second capacitor until voltage at the second capacitor reaches a reference voltage that is greater than the settling voltage; and determining a measure of time for the settling voltage to reach the reference voltage, wherein the measure of time corresponds to a measure of capacitance on the first capacitor. - View Dependent Claims (36, 37, 38, 39, 40, 41)
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- 42. An apparatus comprising a programmable current source coupled to a variable capacitor and a switch network, the switch network configured to couple the programmable current source to a ground potential and to a second capacitor and an input of a voltage measurement circuit.
Specification