Capacitive sensing with low-frequency noise reduction
First Claim
1. A method comprising:
- inducing charge onto a capacitively charged key using a drive signal during a drive part of a measurement cycle;
transferring, during a signal measurement part of the measurement cycle, charge induced on the key during the drive part of the measurement cycle to a signal measurement capacitor;
transferring, during a first noise measurement part of the measurement cycle, charge induced on the key due to noise to a noise measurement capacitor; and
determining an amount of charge induced on the key due to noise during the signal measurement part of the measurement cycle based on an amount of charge transferred to the noise measurement capacitor during the first noise measurement part of the measurement cycle, resulting in a determined noise value.
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Abstract
A method of sensing the presence of a body from a change in an amount of charge present on a capacitively charged key. The method comprises inducing charge onto the key during a drive part of a measurement cycle, coupling a signal measurement capacitor to the key during a signal measurement part of the measurement cycle to the effect that the charge induced on the key during the drive part of the measurement cycle is transferred to the signal measurement capacitor, determining from a noise measurement part of the measurement cycle an amount of charge induced on the key by noise during the signal measurement part of the measurement cycle, and controlling the drive part, the signal measurement part and the noise measurement parts of the cycle to provide the charge sensing circuit with a measurement of the signal from which the noise induced on the key has been or can be substantially cancelled.
30 Citations
30 Claims
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1. A method comprising:
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inducing charge onto a capacitively charged key using a drive signal during a drive part of a measurement cycle; transferring, during a signal measurement part of the measurement cycle, charge induced on the key during the drive part of the measurement cycle to a signal measurement capacitor; transferring, during a first noise measurement part of the measurement cycle, charge induced on the key due to noise to a noise measurement capacitor; and determining an amount of charge induced on the key due to noise during the signal measurement part of the measurement cycle based on an amount of charge transferred to the noise measurement capacitor during the first noise measurement part of the measurement cycle, resulting in a determined noise value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. An apparatus, comprising:
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a driving circuit operable to induce charge onto a capacitively charged key, a charge sensing circuit comprising; a signal measurement capacitor; and a noise measurement capacitor; and a controller, the controller being operable to perform operations comprising; controlling the driving circuit to induce charge onto the key during a drive part of a measurement cycle; controlling the charge sensing circuit to transfer, during a signal measurement part of the measurement cycle, charge induced on the key during the drive part of the measurement cycle to the signal measurement capacitor; controlling the charge sensing circuit to transfer, during a first noise measurement part of the measurement cycle, charge induced on the key due to noise to the noise measurement capacitor; and determining an amount of charge induced on the key due to noise during the signal measurement part of the measurement cycle based on an amount of charge transferred to the noise measurement capacitor during the first noise measurement part of the measurement cycle, resulting in a determined noise value.
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16. A controller operable to perform operations comprising:
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controlling a driving circuit to induce charge onto a capacitively charged key during a drive part of a measurement cycle; controlling a charge sensing circuit, the charge sensing circuit comprising a signal measurement capacitor and a noise measurement capacitor, to transfer, during a signal measurement part of the measurement cycle, charge induced on the key during the drive part of the measurement cycle to the signal measurement capacitor; controlling the charge sensing circuit to transfer, during a first noise measurement part of the measurement cycle, charge induced on the key due to noise to the noise measurement capacitor; and determining an amount of charge induced on the key due to noise during the signal measurement part of the measurement cycle based on an amount of charge transferred to the noise measurement capacitor during the signal measurement part of the measurement cycle, resulting in a determined noise value. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. A device comprising:
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a touch sensor comprising a capacitively charged key; and a controller operable to perform operations comprising; controlling a driving circuit to induce charge onto the capacitively charged key during a drive part of a measurement cycle; controlling a charge sensing circuit, the charge sensing circuit comprising a signal measurement capacitor and a noise measurement capacitor, to transfer, during a signal measurement part of the measurement cycle, charge induced on the key during the drive part of the measurement cycle to the signal measurement capacitor; controlling the charge sensing circuit to transfer, during a first noise measurement part of the measurement cycle, charge induced on the key due to noise to the noise measurement capacitor; and determining an amount of charge induced on the key due to noise during the signal measurement part of the measurement cycle based on an amount of charge transferred to the noise measurement capacitor during the first noise measurement part of the measurement cycle, resulting in a determined noise value.
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Specification