Capacitive Touch Sensor Electrode Pattern for Signal Inversion
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Solution Overview
Problem
The proximity of display electrodes to touch sensor electrodes in thin touch screen stacks leads to signal inversion issues in mutual capacitance measurements, particularly for floating touches, as the self capacitance between these electrodes becomes significant, compromising the accuracy of mutual capacitance measurements.
Innovation Solution
The design involves a capacitive touch sensor with drive and sense electrodes arranged under a dielectric touch panel, where the width of the Y electrode portions and the gap between them are optimized relative to the touch panel thickness to mitigate signal inversion, allowing for accurate mutual capacitance measurements by ensuring the mutual capacitance between groups is smaller than within groups, and the electrodes are arranged to provide good grounding for floating touches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the touch panel thickness is reduced to create thinner touch screen stacks, then the overall device thickness is reduced, but the self capacitance between display electrodes and touch sensor electrodes becomes significant, causing signal inversion issues in mutual capacitance measurements
Solution Approach 1:
The patent applies local quality by creating non-uniform electrode width and gap configurations at different locations. Specifically, the drive electrode width and sense electrode gap are varied across different regions of the touch sensor array to locally compensate for the increased self-capacitance effect in thinner panels, thereby maintaining measurement precision without increasing overall thickness
Solution Approach 2:
The patent changes physical parameters of the electrode structure, specifically adjusting electrode widths and gaps between electrodes. By modifying these geometric parameters, the patent optimizes the balance between self-capacitance and mutual-capacitance measurements, enabling accurate touch detection in thin panel configurations
2Measurement precision
If the electrode width and gap are optimized to mitigate signal inversion, then measurement accuracy is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent segments the electrode array into multiple groups with different width-gap configurations. This segmentation allows the system to use multiple measurement patterns rather than relying on a single critical configuration, thereby reducing the impact of manufacturing variations on overall measurement accuracy
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively reduces signal inversion and maintains sensitivity and linearity in touch determination, enabling accurate detection of touch location and size regardless of grounding conditions, even in thin touch screen stacks.
Implementation Method 1
Changes in the mutual capacitance between a drive electrode and a sense electrode provide the measurement signal
Implementation Method 2
the self capacitance between these electrodes becomes significant, compromising the accuracy of mutual capacitance measurements
Data Source
AI summary
In a capacitive touch sensor device, to avoid floating touches causing signal inversion in mutual capacitance measurements, an electrode pattern is used of the type in which the mutual capacitance arises primarily from co-extending electrode portions of the drive and sense electrodes separated by a gap G. The pattern is dimensioned such that the sum of the gap G between co-extending drive and sense electrode portions and the widths Wy of the sense electrodes is made sufficiently small to avoid signal inversion. Namely, the width, Wy, plus the gap, G, is made less than or equal to one of: 4, 3 or 2 times the distance from the touch sensor electrodes to the touch surface, this distance being the touch panel thickness, h.