NOISE CANCELLATION TECHNIQUE FOR CAPACITIVE TOUCHSCREEN CONTROLLER USING DIFFERENTIAL SENSING
First Claim
1. A method of detecting one or more touch events on a touch sensitive device comprising;
- a. receiving a plurality of channels, each channel having sensed data corresponding to the touch sensitive device;
b. measuring a capacitance of each channel when no touch event is present on any of the plurality of channels, thereby determining a no touch baseline value for each channel;
c. selecting one of the plurality of channels as a primary channel;
d. selecting another of the plurality of channels as a references channel, wherein the reference channel is different than the primary channel;
e. measuring a capacitance of the primary channel;
f. measuring a capacitance of the reference channel;
g. calculating a difference between the measured capacitance of the primary channel and the measured capacitance of the reference channel, thereby determining a measured difference;
h. calculating a difference between the no touch baseline value for the primary channel and the no touch baseline value for the reference channel, thereby determining a baseline difference;
i. calculating a difference between the measured difference and the baseline difference, thereby determining a delta from baseline for the primary channel and reference channel pair;
j. repeating steps c-h for each channel in the plurality of channels so that each channel is selected as the primary channel; and
k. determining one or more touch events from the delta from baselines calculated for all primary channel and reference channel pairs.
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Accused Products
Abstract
A differential sensing scheme provides a means for detecting one or more touch events on a touch sensitive device in the presence of incident noise. Instead of sensing one touch sensitive channel, such as a row, column, or single touch sensor, multiple touch sensitive channels are sampled at a time. By sampling two nearby channels simultaneously and doing the measurement differentially, noise common to both channels is cancelled. The differential sensing scheme is implemented using simple switch-capacitor AFE circuitry. The originally sensed data on each individual channel is recovered free of common-mode noise. The recovered sensed data is used to determine the presence of one or more touch events and if present the location of each touch event on the touch sensitive device.
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Citations
31 Claims
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1. A method of detecting one or more touch events on a touch sensitive device comprising;
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a. receiving a plurality of channels, each channel having sensed data corresponding to the touch sensitive device; b. measuring a capacitance of each channel when no touch event is present on any of the plurality of channels, thereby determining a no touch baseline value for each channel; c. selecting one of the plurality of channels as a primary channel; d. selecting another of the plurality of channels as a references channel, wherein the reference channel is different than the primary channel; e. measuring a capacitance of the primary channel; f. measuring a capacitance of the reference channel; g. calculating a difference between the measured capacitance of the primary channel and the measured capacitance of the reference channel, thereby determining a measured difference; h. calculating a difference between the no touch baseline value for the primary channel and the no touch baseline value for the reference channel, thereby determining a baseline difference; i. calculating a difference between the measured difference and the baseline difference, thereby determining a delta from baseline for the primary channel and reference channel pair; j. repeating steps c-h for each channel in the plurality of channels so that each channel is selected as the primary channel; and k. determining one or more touch events from the delta from baselines calculated for all primary channel and reference channel pairs. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method of detecting one or more touch events on a touch panel comprising;
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a. receiving a plurality of channels, each channel having sensed data corresponding to the touch panel; b. determining a capacitance of each channel when no touch event is present on any of the plurality of channels, thereby determining a no touch baseline value for each channel; c. selecting two of the plurality of channels and calculating a difference between the no touch baseline value for the two channels, thereby determining a baseline difference; d. measuring a capacitance of each of the selected two channels; e. calculating a difference between the measured capacitances of the two channels, thereby determining a measured difference where a common-mode noise present in both of the selectively measured two channel is removed; f. calculating a difference between the measured difference and the baseline difference, thereby determining a delta from baseline for the two channels; g. repeating steps c-f for additional channel pairs in the plurality of channels; and h. recovering the sensed data from all the delta from baselines for the channel pairs, wherein the recovered sensed data does not include common-mode noise present in the sensed data; and i. determining one or more touch events from the recovered sensed data. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. A method of detecting one or more touch events on a touch panel comprising;
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a. receiving a plurality of channels, each channel having sensed data corresponding to the touch panel; b. determining a capacitance of each channel when no touch event is present on any of the plurality of channels, thereby determining a no touch baseline value for each channel; c. selecting N of the plurality of channels and calculating a difference between the no touch baseline value for the N channels, thereby determining a baseline difference; d. measuring a capacitance of each of the selected N channels; e. calculating a difference between the measured capacitances of the N channels, thereby determining a measured difference where a common-mode noise present in the selectively measured N channels is removed; f. calculating a difference between the measured difference and the baseline difference, thereby determining a delta from baseline for the N channels; g. repeating steps c-f for additional channel sets in the plurality of channels; h. recovering the sensed data from all the delta from baselines for the channel sets, wherein the recovered sensed data does not include common-mode noise present in the sensed data; and i. determining one or more touch events from the recovered sensed data.
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31. An apparatus for detecting one or more touch events on a touch panel comprising;
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a. means for receiving a plurality of channels, each channel having sensed data corresponding to the touch panel; b. means for determining a capacitance of each channel when no touch event is present on any of the plurality of channels, thereby determining a no touch baseline value for each channel; c. means for selecting N of the plurality of channels and calculating a difference between the no touch baseline value for the N channels, thereby determining a baseline difference; d. means for measuring a capacitance of each of the selected N channels; e. means for calculating a difference between the measured capacitances of the N channels, thereby determining a measured difference where a common-mode noise present in the selectively measured N channels is removed; f. means for calculating a difference between the measured difference and the baseline difference, thereby determining a delta from baseline for the N channels; g. means for repeating steps c-f for additional channel sets in the plurality of channels; h. means for recovering the sensed data from all the delta from baselines for the channel sets, wherein the recovered sensed data does not include common-mode noise present in the sensed data; and i. means for determining one or more touch events from the recovered sensed data.
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Specification