Capacitive Touch Ground Bars for Negative Pixel Reduction
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Solution Overview
Problem
Mutual capacitance touch sensor panels face challenges in detecting poorly grounded or ungrounded objects due to reduced capacitive coupling, leading to decreased touch detection accuracy and the occurrence of 'negative pixels' which result in touch detection errors.
Innovation Solution
Incorporating mutual capacitance unit cells with a drive electrode, a sense electrode, and one or more ground bars that provide an increased capacitive path to ground, reducing mutual capacitance between electrodes and minimizing charge coupling back onto nearby sense electrodes, thereby enhancing touch detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mutual capacitance touch sensing is used to detect touches, then touch detection capability is improved, but poorly grounded or ungrounded objects cause negative pixels and touch detection errors
Solution Approach 1:
A ground electrode is introduced as an intermediary element between the poorly grounded object and the sense electrode. This ground electrode provides a dedicated capacitive path to ground, preventing charge from coupling back onto the sense electrode and causing negative pixels. The ground electrode acts as a mediator that captures stray capacitive coupling and directs it to ground, thereby eliminating the harmful effect on touch detection accuracy.
Solution Approach 2:
The touch sensor structure is segmented by adding a separate ground electrode layer distinct from the drive and sense electrodes. This segmentation allows the ground electrode to independently manage capacitive coupling paths, separating the function of charge detection (sense electrode) from charge dissipation (ground electrode), thereby preventing interference and negative pixel formation.
2Reliability
If ground bars are added to provide increased capacitive path to ground, then touch detection accuracy is improved, but device complexity increases
Solution Approach 1:
The ground electrode serves multiple functions simultaneously: it provides a capacitive path to ground for poorly grounded objects, prevents negative pixel formation, and does not interfere with normal mutual capacitance sensing. By making the ground electrode multi-functional, the design achieves improved reliability without proportionally increasing complexity, as the same structure addresses multiple problems.
Solution Approach 2:
Ground bars are strategically placed in specific locations where negative pixels are most likely to occur, such as at the corners or edges of the touch sensor panel. This localized approach provides ground paths only where needed, rather than requiring a complete ground network across the entire panel, thereby minimizing the increase in device complexity while still improving touch detection accuracy in critical areas.
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
The proposed touch electrode architecture improves touch detection accuracy by increasing the capacitive path for poorly grounded objects, reducing negative pixels and associated errors, and enhancing the reliability of touch detection in mutual capacitance touch sensor panels.
Implementation Method 1
Capacitive touch sensor panels detect a touch, or a near-touch, of a proximate object by detecting the effect of capacitive coupling between the object and the touch electrodes
Implementation Method 2
When the object is well-grounded, the capacitive coupling can couple charge to ground through the object. In the case of mutual capacitance touch sensing, this coupling of charge to ground reduces the mutual capacitance between the drive electrode and the sense electrode
Data Source
AI summary
Touch electrode architectures for reducing the occurrence of negative pixels in mutual capacitance touch sensor panels that are caused by poorly grounded objects are disclosed. A touch electrode architecture can utilize mutual capacitance unit cells, each of which include a drive electrode, a sense electrode, and one or more ground bars. The one or more ground bars can provide an increased capacitive path to ground for a poorly grounded finger, which can result in a larger reduction in mutual capacitance between the drive and sense electrodes, improving touch detection. In addition, the increased capacitive coupling between the object and ground reduces the amount of charge that couples back onto nearby sense electrodes, which can reduce the negative pixel that can occur at those electrodes and reduce the number of touch detection errors. The one or more ground bars can be formed in the same layer as the drive electrode.