Capacitive sensor with ratiometric voltage references
First Claim
1. An apparatus, comprising:
- a voltage source to generate a first voltage reference and a second voltage reference in response to a supply voltage;
a charge transfer switch coupled to an integrating capacitor having a first plate and a second plate coupled to a reference voltage rail to distribute charge between a sensing capacitor and the integrating capacitor, the charge accumulated in response to the first voltage reference;
a control switch coupled to the first plate of the integrating capacitor to selectively disconnect the first plate of the integrating capacitor from a reference voltage node to maintain an integrated charge on the integrating capacitor; and
a comparator coupled to the second voltage reference and the integrating capacitor to compare a voltage proportional to the integrated charge on the integrating capacitor against the second voltage reference, wherein the first voltage reference changes proportionally to the second voltage reference in response to a change in the supply voltage.
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Accused Products
Abstract
A capacitive sensor with ratiometric voltage references includes a voltage source, a charge transfer switch, an integrating capacitor, and a comparator. The voltage source is configured to generate a first voltage reference and a second voltage reference in response to a supply voltage, where the first voltage reference changes proportionally to the second voltage reference in response to a change in the supply voltage. The charge transfer switch is coupled to the integrating capacitor to distribute charge between a sensing capacitor and the integrating capacitor, where the charge is accumulated in response to the first voltage reference. The comparator is coupled to the second voltage reference and the integrating capacitor to compare a voltage on the integrating capacitor against the second voltage reference.
44 Citations
21 Claims
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1. An apparatus, comprising:
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a voltage source to generate a first voltage reference and a second voltage reference in response to a supply voltage; a charge transfer switch coupled to an integrating capacitor having a first plate and a second plate coupled to a reference voltage rail to distribute charge between a sensing capacitor and the integrating capacitor, the charge accumulated in response to the first voltage reference; a control switch coupled to the first plate of the integrating capacitor to selectively disconnect the first plate of the integrating capacitor from a reference voltage node to maintain an integrated charge on the integrating capacitor; and a comparator coupled to the second voltage reference and the integrating capacitor to compare a voltage proportional to the integrated charge on the integrating capacitor against the second voltage reference, wherein the first voltage reference changes proportionally to the second voltage reference in response to a change in the supply voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method of operating a capacitance sensor, comprising:
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outputting a first voltage reference and a second voltage reference from a voltage source in response to a supply voltage; accumulating a charge in response to the first voltage reference; distributing the charge between a sensing capacitor and an integrating capacitor; maintaining an integrated charge on the integrating capacitor after the distributing; and comparing a voltage proportional to the integrated charge on the integrating capacitor with the second voltage reference to determine whether the voltage on the integrating capacitor is greater than or less than the second voltage reference, wherein the first voltage reference changes proportionally to the second voltage reference in response to a change in the supply voltage. - View Dependent Claims (16, 17, 18, 19)
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20. An apparatus, comprising:
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means for generating a first voltage reference and a second voltage reference in response to a supply voltage; means for accumulating a charge in response to the first voltage reference; means for distributing the charge between a sensing capacitor and an integrating capacitor; means for maintaining an integrated charge on the integrating capacitor after distributing; and means for comparing a voltage proportional to the integrated charge on the integrating capacitor with the second voltage reference to determine whether the voltage on the integrating capacitor is greater than or less than the second voltage reference, wherein the first voltage reference changes proportionally to the second voltage reference in response to a change in the supply voltage. - View Dependent Claims (21)
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Specification