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:
- measuring a capacitance of each channel of a plurality of channels when no touch event is present on any of the plurality of channels for determining a no touch baseline value for each channel;
selecting one of the plurality of channels as a primary channel;
selecting another of the plurality of channels as a reference channel, wherein the reference channel is different than the primary channel;
measuring a capacitance of the primary channel;
measuring a capacitance of the reference channel;
calculating a difference between the measured capacitance of the primary channel and the measured capacitance of the reference channel for determining a measured difference;
calculating a difference between the no touch baseline value for the primary channel and the no touch baseline value for the reference channel for determining a baseline difference;
calculating a difference between the measured difference and the baseline difference for determining a delta from baseline for the primary channel and reference channel pair;
repeating the steps of selecting one of the plurality of channels as a primary channel, selecting another of the plurality of channels as a reference channel, measuring a capacitance of the primary channel, measuring a capacitance of the reference channel, calculating a difference between the measured capacitance of the primary channel and the measured capacitance of the reference channel, calculating a difference between the no touch baseline value for the primary channel and the no touch baseline value for the reference channel, and calculating a difference between the measured difference and the baseline difference for determining a delta from baseline for the primary channel and reference channel pair for each channel in the plurality of channels so that each channel is selected as the primary channel; and
determining one or more touch events from the delta from baselines calculated for all primary channel and reference channel pairs.
4 Assignments
0 Petitions
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.
89 Citations
30 Claims
-
1. A method of detecting one or more touch events on a touch sensitive device comprising:
-
measuring a capacitance of each channel of a plurality of channels when no touch event is present on any of the plurality of channels for determining a no touch baseline value for each channel; selecting one of the plurality of channels as a primary channel; selecting another of the plurality of channels as a reference channel, wherein the reference channel is different than the primary channel; measuring a capacitance of the primary channel; measuring a capacitance of the reference channel; calculating a difference between the measured capacitance of the primary channel and the measured capacitance of the reference channel for determining a measured difference; calculating a difference between the no touch baseline value for the primary channel and the no touch baseline value for the reference channel for determining a baseline difference; calculating a difference between the measured difference and the baseline difference for determining a delta from baseline for the primary channel and reference channel pair; repeating the steps of selecting one of the plurality of channels as a primary channel, selecting another of the plurality of channels as a reference channel, measuring a capacitance of the primary channel, measuring a capacitance of the reference channel, calculating a difference between the measured capacitance of the primary channel and the measured capacitance of the reference channel, calculating a difference between the no touch baseline value for the primary channel and the no touch baseline value for the reference channel, and calculating a difference between the measured difference and the baseline difference for determining a delta from baseline for the primary channel and reference channel pair for each channel in the plurality of channels so that each channel is selected as the primary channel; and 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)
-
-
17. A method of detecting one or more touch events on a touch panel comprising:
-
determining a capacitance of each channel of a plurality of channels when no touch event is present on any of the plurality of channels for determining a no touch baseline value for each channel; selecting two of the plurality of channels and calculating a difference between the no touch baseline value for the two channels for determining a baseline difference; measuring a capacitance of each of the selected two channels; calculating a difference between the measured capacitances of the two channels for determining a measured difference; calculating a difference between the measured difference and the baseline difference for determining a delta from baseline for the two channels; repeating the steps of selecting two of the plurality of channels and calculating a difference between the no touch baseline value for the two channels, measuring a capacitance of each of the selected two channels, calculating a difference between the measured capacitances of the two channels, and calculating a difference between the measured difference and the baseline difference, for additional channel pairs in the plurality of channels;
for additional channel pairs in the plurality of channels;recovering 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 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)
-
-
30. A method of detecting one or more touch events on a touch panel comprising:
-
determining a capacitance of each channel of a plurality of channels when no touch event is present on any of the plurality of channels for determining a no touch baseline value for each channel; selecting N of the plurality of channels and calculating a difference between the no touch baseline value for the N channels for determining a baseline difference; measuring a capacitance of each of the selected N channels; calculating a difference between the measured capacitances of the N channels for determining a measured difference; calculating a difference between the measured difference and the baseline difference for determining a delta from baseline for the N channels; repeating the steps of selecting N of the plurality of channels and calculating a difference between the no touch baseline value for the N channels, measuring a capacitance of each of the selected N channels, calculating a difference between the measured capacitances of the N channels, and calculating a difference between the measured difference and the baseline difference, for additional channel sets in the plurality of channels; recovering sensed data from all the delta from baselines for the channel sets; and determining one or more touch events from the recovered sensed data.
-
Specification