Noise filtering devices, systems and methods for capacitance sensing devices
First Claim
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1. A capacitance sensing system, comprising:
- a capacitance sense network comprising a plurality of electrodes for generating sense values;
a power supply interface;
a noise listening circuit configured to detect noise on a plurality of the electrodes, and vary its operation, including being enabled and disabled, in response to whether a power supply interface is or is not, respectively, receiving power from a source external to the capacitance sensing system; and
a filtering circuit configured to provide first filtering to position detection signals output from the capacitance sense network when noise is detected by the noise listening circuit, and to provide second filtering to the position detection signals when noise is not detected by the noise listening circuit.
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Abstract
A capacitance sensing system can filter noise that presents in a subset of electrodes in the proximity of a sense object (i.e., finger). A capacitance sensing system can include a sense network comprising a plurality of electrodes for generating sense values; a noise listening circuit configured to detect noise on a plurality of the electrodes; and a filtering circuit that enables a filtering for localized noise events when detected noise values are above one level, and disables the filtering for localized noise events when detected noise values are below the one level.
33 Citations
17 Claims
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1. A capacitance sensing system, comprising:
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a capacitance sense network comprising a plurality of electrodes for generating sense values; a power supply interface; a noise listening circuit configured to detect noise on a plurality of the electrodes, and vary its operation, including being enabled and disabled, in response to whether a power supply interface is or is not, respectively, receiving power from a source external to the capacitance sensing system; and a filtering circuit configured to provide first filtering to position detection signals output from the capacitance sense network when noise is detected by the noise listening circuit, and to provide second filtering to the position detection signals when noise is not detected by the noise listening circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A capacitance sensing system, comprising:
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a touchscreen; a mutual capacitance sense network coupled to the touchscreen and comprising a plurality of transmit (TX) electrodes and a plurality of receive (RX) electrodes; a noise listening circuit configured to detect at least one noise source and vary its operation, including being enabled and disabled, in response to whether a power supply interface is or is not, respectively, receiving power from a source external to the capacitance sensing system; and a controller configured to operate in a noise detection mode and a position detection mode, and including a switch circuit and a filtering circuit, wherein in the noise detection mode, the switch circuit couples the electrodes of the sense network to a capacitance sensing circuit in a first configuration, in the position detection mode, the switch circuit couples the electrodes of the sense network to the capacitance sensing circuit in a second configuration different than the first configuration; and the filtering circuit is configured to provide first filtering to values generated from the sense network when the one noise source is detected by the noise listening circuit, and to provide second filtering to the position detection signals when the one noise source is not detected by the noise listening circuit. - View Dependent Claims (10, 11, 12, 13)
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14. A method of filtering sense inputs of a touchscreen device, comprising:
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selectively determining if a touchscreen with a mutual capacitance sensing network is receiving noise from at least one predetermined source with a noise listening circuit; selectively varying an operation of the noise listening circuit, including being enabled or disabled, in response to whether the touchscreen device is or is not, respectively, receiving external power through a power supply interface; if the noise is not being received, filtering capacitance sense input values generated from the sensing network with a common mode noise filter and a first number of scans of electrodes within the sensing network; and if the noise is being received, filtering capacitance sense input values with filtering that does not include the common mode noise filter and with a second number of scans greater than the first number of scans. - View Dependent Claims (15, 16, 17)
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Specification