Capacitance measurement systems and methods
First Claim
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1. A system for measuring capacitance, said system comprising:
- an adjustable current source supplying a substantially constant current that charges a first capacitor and a second capacitor until voltage at said second capacitor settles to a settling voltage, wherein during said charging said first capacitor is alternately switched between said current source and ground, and wherein said first capacitor is electrically coupled to said second capacitor when switched to said current source, and wherein said first capacitor is electrically disconnected from said second capacitor when switched to ground, and wherein charging of said first capacitor is halted after said settling voltage is reached;
a comparator coupled to said second capacitor that compares voltage at said second capacitor to a reference voltage, wherein after charging of said first capacitor is halted, said current source continues to charge said second capacitor until voltage at said second capacitor reaches said reference voltage; and
a counter coupled to said comparator that determines an amount of time until voltage at said second capacitor reaches said reference voltage, wherein said amount of time corresponds to an amount of capacitance on said first capacitor.
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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
25 Claims
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1. A system for measuring capacitance, said system comprising:
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an adjustable current source supplying a substantially constant current that charges a first capacitor and a second capacitor until voltage at said second capacitor settles to a settling voltage, wherein during said charging said first capacitor is alternately switched between said current source and ground, and wherein said first capacitor is electrically coupled to said second capacitor when switched to said current source, and wherein said first capacitor is electrically disconnected from said second capacitor when switched to ground, and wherein charging of said first capacitor is halted after said settling voltage is reached; a comparator coupled to said second capacitor that compares voltage at said second capacitor to a reference voltage, wherein after charging of said first capacitor is halted, said current source continues to charge said second capacitor until voltage at said second capacitor reaches said reference voltage; and a counter coupled to said comparator that determines an amount of time until voltage at said second capacitor reaches said reference voltage, wherein said amount of time corresponds to an amount of capacitance on said first capacitor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of measuring capacitance, said method comprising:
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charging, by an adjustable current source supplying a constant current, a first capacitor and a second capacitor until voltage at said second capacitor settles to a settling voltage, wherein during said charging said first capacitor is switched back and forth between said current source and ground; when said settling voltage is reached, halting charging of said first capacitor while continuing to charge said second capacitor, by said adjustable current source, until voltage at said second capacitor reaches a reference voltage that is greater than said settling voltage; and determining a measure of time for voltage at said second capacitor to reach said reference voltage, wherein said determining comprises counting a first number of oscillatory cycles, said counting starting at the time charging of the first capacitor is halted, until said voltage at said second capacitor reaches said reference voltage, wherein said first number corresponds to said measure of capacitance on said first capacitor. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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19. A system for measuring capacitance, said system comprising:
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a first capacitor coupled to an adjustable current source supplying a constant current; a second capacitor coupled to said current source in parallel to said first capacitor; switching circuitry for controlling charging of said first capacitor and said second capacitor, wherein in a first operating stage both said first capacitor and said second capacitor are charged by said current source until voltages at said second capacitor and said first capacitor equilibrate at a settling voltage, and wherein in a second operating stage said second capacitor but not said first capacitor is charged by said current source until voltage at said second capacitor increases to a reference voltage, and wherein further said switching circuitry alternately switches said first capacitor between said current source and ground during said first operating stage; and processing circuitry coupled to said second capacitor for determining a measure of capacitance on said first capacitor based on how long it takes for voltage at said second capacitor to increase from said settling voltage to said reference voltage. - View Dependent Claims (20, 21, 22, 23, 24, 25)
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Specification