Capacitance measurement system and methods
First Claim
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1. A system for measuring capacitance comprising:
- 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 supply charge to the first and second capacitors, wherein the charge supplied to the first and second capacitors generates a voltage potential across the first and second capacitors;
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;
a second switch configured to couple the first node of the first capacitor to a second node of the second capacitor; and
a 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 after a voltage potential across the first capacitor has reached a settling voltage, andthe current source is configured to provide a charge on the first capacitor according to a predetermined charge rate.
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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.
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Citations
26 Claims
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1. A system for measuring capacitance 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 supply charge to the first and second capacitors, wherein the charge supplied to the first and second capacitors generates a voltage potential across the first and second capacitors; 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; a second switch configured to couple the first node of the first capacitor to a second node of the second capacitor; and a 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 after a voltage potential across the first capacitor has reached a settling voltage, and the current source is configured to provide a charge on the first capacitor according to a predetermined charge rate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. 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 multiplexer bus; coupling a second capacitor to the multiplexer bus; charging a first capacitor and a second capacitor until voltage at said second capacitor settles to a settling voltage derived from the current source, a settling time, and the capacitance of the first capacitor, wherein during said charging said first capacitor is switched back and forth between a current source and ground; when said settling voltage is reached, halting charging of said first capacitor while continuing to charge said second capacitor until voltage at said second capacitor reaches a reference voltage that is greater than said settling voltage; and determining a measure of time for said settling voltage to reach said reference voltage, wherein said measure of time corresponds to a measure of capacitance on said first capacitor. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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- 21. An apparatus comprising a programmable current source coupled to a first variable capacitor and a switch network, the switch network configured to couple the programmable current source alternately to a ground potential and to a second capacitor and an input of a voltage measurement circuit, wherein the programmable current source is coupled to the second capacitor only after the voltage on the first variable capacitor and the second capacitor reaches a settling voltage.
Specification