Compensation for parasitic capacitance of a capacitive sensor
First Claim
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1. An apparatus, comprising:
- a sensor capacitor;
a modulation capacitor coupled with the sensor capacitor and configured to receive charge from the sensor capacitor;
compensation circuitry coupled with the sensor capacitor and the modulation capacitor, wherein the compensation circuitry is configured to divert a portion of the charge from the modulation capacitor, and wherein the portion of the charge diverted is based on an amount of a parasitic capacitance of the sensor capacitor measured during a calibration of the compensation circuitry; and
a comparator circuit coupled with the modulation capacitor, wherein the comparator circuit is configured to discharge the modulation capacitor in response to detecting that the charge on the modulation capacitor exceeds a predetermined threshold;
wherein the comparator circuit produces a digital code based on a frequency of the discharge of the modulation capacitor.
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Abstract
An apparatus for converting a capacitance measured on a capacitive sensor to a digital code may include a modulation capacitor to receive charge transferred from the sensor and compensation circuitry to divert charge from the modulation capacitor. A method for operating the apparatus may include generating a digital bitstream based on the capacitance of the sensor and compensating for a parasitic capacitance of the capacitive sensor.
56 Citations
21 Claims
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1. An apparatus, comprising:
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a sensor capacitor; a modulation capacitor coupled with the sensor capacitor and configured to receive charge from the sensor capacitor; compensation circuitry coupled with the sensor capacitor and the modulation capacitor, wherein the compensation circuitry is configured to divert a portion of the charge from the modulation capacitor, and wherein the portion of the charge diverted is based on an amount of a parasitic capacitance of the sensor capacitor measured during a calibration of the compensation circuitry; and a comparator circuit coupled with the modulation capacitor, wherein the comparator circuit is configured to discharge the modulation capacitor in response to detecting that the charge on the modulation capacitor exceeds a predetermined threshold;
wherein the comparator circuit produces a digital code based on a frequency of the discharge of the modulation capacitor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method, comprising:
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charging a sensor capacitor; transferring charge from the sensor capacitor to a modulation capacitor; generating a digital bitstream based on a capacitance of the sensor capacitor; and compensating for a parasitic capacitance of the sensor capacitor by diverting charge from the modulation capacitor through compensation circuitry, and wherein an amount of the diverted charge is based on an amount of the parasitic capacitance measured during a calibration of the compensation circuitry. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. An apparatus, comprising:
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means for generating a digital bitstream based on a capacitance of a sensor capacitor; and means for compensating for a parasitic capacitance of the sensor capacitor by diverting charge from a modulation capacitor through compensation circuitry, and wherein an amount of the diverted charge is based on an amount of the parasitic capacitance measured during a calibration of the compensation circuitry. - View Dependent Claims (21)
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Specification