Capacitive Touch Sensor Electrode Segmentation for Distortion Control
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Solution Overview
Problem
Current two-dimensional capacitive touch screens face challenges in achieving low-cost, large-area, transparent, and low-distortion designs with a minimal number of external connections, while also being prone to geometric distortions and thermal errors.
Innovation Solution
A two-dimensional position sensor design featuring a substrate with interleaved x-electrodes and y-electrodes, where the x-electrodes are grouped to provide ratiometric capacitive signals across the sensitive area, and a central spine for external connection efficiency, reducing the need for numerous external lines and minimizing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If traditional capacitive touch screen designs are used, then transparency and large area are achieved, but geometric distortion and thermal errors increase
Solution Approach 1:
The electrode system is segmented into multiple groups (first, second, third groups of x-electrodes and multiple y-electrodes) that can be independently controlled and measured. This segmentation allows for localized measurement and correction of geometric distortions across different regions of the large screen area, maintaining position accuracy while enabling large screen size.
Solution Approach 2:
Different electrode groups are assigned different functions: x-electrodes provide ratiometric capacitive signals for x-position determination, while y-electrodes provide signals for y-position determination. This local differentiation of electrode functionality enables precise position measurement while compensating for geometric distortions that vary across different regions of the screen.
2Measurement precision
If more external connections are added to reduce distortion, then measurement precision improves, but device complexity increases
Solution Approach 1:
Multiple x-electrodes are merged into three functional groups and multiple y-electrodes are merged into functional sets, all connected to a single common potential. This merging reduces the number of external connections required while maintaining the ability to measure and correct geometric distortions across the entire screen area, balancing precision with simplicity.
Solution Approach 2:
The common potential connection serves multiple functions: it provides a reference potential for all electrode groups, enables ratiometric measurements for position determination, and facilitates geometric distortion correction. This multi-functionality reduces the need for separate dedicated connections for each function, simplifying the overall connection architecture.
3Measurement precision
If electrode density is increased to improve resolution, then measurement precision improves, but manufacturing cost increases
Solution Approach 1:
The system uses dynamic signal processing where ratiometric capacitive signals from multiple electrode groups are processed to determine position. This dynamic approach allows achieving high resolution with fewer physical electrodes by utilizing the combined information from multiple electrode groups, reducing manufacturing complexity and cost while maintaining high position resolution.
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 achieves quasi-continuous x-resolution and step-like y-resolution with a reduced number of external connections, enhancing accuracy and scalability, particularly suitable for larger screen sizes without significant handshadow effects.
Implementation Method 1
two-dimensional capacitive transducer or 2DCT is used as a generic term for touch screens, touch sensing pads, proximity sensing areas... having a surface or volume capable of reporting at least a 2-dimensional coordinate... by means of a capacitance sensing mechanism
Data Source
AI summary
A position sensor comprises first and second electrodes that generally extend in a first direction and are arranged in a pattern that defines a sensitive area, the second electrodes interleaved with the first electrodes in a second direction. The first electrodes comprise first, second, and third groups of elements, elements in the first, second, and third groups being connected to each other but not to elements in another group. The elements have shapes configured for adjacent elements in the first and second groups to co-extend in the first direction over a first portion of the sensitive area and to provide ratiometric capacitive signals with respect to each other in the first direction, and adjacent elements in the second and third groups to co-extend in the first direction over a second portion of the sensitive area and to provide ratiometric capacitive signals with respect to each other in the first direction.