Capacitive sensing with high-frequency noise reduction
First Claim
1. A method, comprising:
- generating a plurality of signal sample values from a plurality of measurement cycles, each of the measurement cycles comprising;
inducing charge onto a capacitive key;
measuring the charge induced on the capacitive key; and
generating a signal sample value representing the charge measured from the capacitive key; and
processing the plurality of signal sample values to obtain a plurality of processed signal sample values, the processing comprising limiting a rate of change between a first processed signal sample value and a second processed signal sample value to a maximum rate of change;
wherein limiting the rate of change between the first processed signal sample value and the second processed signal sample value to a maximum rate of change comprises determining a rate of change between the second processed signal sample value and a first signal sample value.
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Accused Products
Abstract
A method and apparatus for sensing the presence of a body from a change in an amount of charge present on a capacitively charged key includes performing a measurement burst which generates a plurality of signal sample values from a plurality of measurement cycles. Each of the measurement cycle includes inducing charge onto the key during a drive part of the measurement cycle, measuring during a signal measurement part of the measurement cycle the charge induced on the key during the drive part of the measurement cycle, and generating a signal sample value to represent of the charge measured from the key during the signal measurement part of the measurement cycle. The method includes comparing the value of the plurality of the signal sample values of the measurement burst with a determined range of accepted values between a determined maximum and a determined minimum value, and processing any of the plurality of signal sample values, which are outside the determined accepted range to the effect that the presence of the body can be determined only from a change in the value of one or more of the plurality of signal samples which are within the determined accepted range. By removing the effects of signal sample values, which are outside the determined accepted range of values, then the effects of noise, such as rectangular noise, which might otherwise cause a body to be erroneously detected can be substantially reduced.
18 Citations
20 Claims
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1. A method, comprising:
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generating a plurality of signal sample values from a plurality of measurement cycles, each of the measurement cycles comprising; inducing charge onto a capacitive key; measuring the charge induced on the capacitive key; and generating a signal sample value representing the charge measured from the capacitive key; and processing the plurality of signal sample values to obtain a plurality of processed signal sample values, the processing comprising limiting a rate of change between a first processed signal sample value and a second processed signal sample value to a maximum rate of change; wherein limiting the rate of change between the first processed signal sample value and the second processed signal sample value to a maximum rate of change comprises determining a rate of change between the second processed signal sample value and a first signal sample value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An apparatus, comprising:
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a driving circuit operable to induce charge onto a capacitive key; a charge sensing circuit comprising a signal measurement capacitor; and a controller, the controller being operable to perform operations comprising; controlling the driving circuit and the charge sensing circuit to generate a plurality of signal sample values from a plurality of measurement cycles, each of the measurement cycles comprising; inducing charge onto the capacitive key; measuring the charge induced on the capacitive key; and generating a signal sample value representing the charge measured from the capacitive key; and processing the plurality of signal sample values to obtain a plurality of processed signal sample values, the processing comprising limiting a rate of change between a first processed signal sample value and a second processed signal sample value to a maximum rate of change; wherein limiting the rate of change between the first processed signal sample value and the second processed signal sample value to a maximum rate of change comprises determining a rate of change between the second processed signal sample value and a first signal sample value. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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17. A controller, comprising:
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one or more processors; and one or more computer-readable non-transitory storage media embodying logic configured when executed by the one or more processors to perform operations comprising; controlling a driving circuit and a charge sensing circuit, the charge sensing circuit comprising a signal measurement capacitor, to generate a plurality of signal sample values from a plurality of measurement cycles, each of the measurement cycles comprising; inducing charge onto a capacitive key; measuring the charge induced on the capacitive key; and generating a signal sample value representing the charge measured from the capacitive key; and processing the plurality of signal sample values to obtain a plurality of processed signal sample values, the processing comprising limiting a rate of change between a first processed signal sample value and a second processed signal sample value to a maximum rate of change; wherein limiting the rate of change between the first processed signal sample value and the second processed signal sample value to a maximum rate of change comprises determining a rate of change between the second processed signal sample value and a first signal sample value. - View Dependent Claims (18, 19)
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20. An apparatus, comprising:
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means for generating a plurality of signal sample values from a plurality of measurement cycles, each of the measurement cycles comprising; inducing charge onto a capacitive key; measuring the charge induced on the capacitive key; and generating a signal sample value representing the charge measured from the capacitive key; and means for processing the plurality of signal sample values to obtain a plurality of processed signal sample values, the processing comprising limiting a rate of change between a first processed signal sample value and a second processed signal sample value to a maximum rate of change, wherein limiting the rate of change between the first processed signal sample value and the second processed signal sample value to a maximum rate of change comprises determining a rate of change between the second processed signal sample value and a first signal sample value.
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Specification