Asymmetric Touch Sensor Electrode Fill Factor for Ground Plane Interference
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Solution Overview
Problem
Touch screens on display devices face reduced sensitivity due to interference from a ground plane or pixel electrode circuit, which limits the accuracy of determining the touched position.
Innovation Solution
A display device with a touch sensor structure featuring non-parallel electrode arrays, where one array has a higher fill factor closer to the display layer and a lower fill factor farther away, with asymmetric enlarged portions along straight electrode lines, to enhance sensitivity by shielding electromagnetic signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the fill factor of sensing electrodes is increased to maximize the signal, then the touch screen sensitivity improves, but the interference from the ground plane increases due to more field lines being trapped between electrodes
Solution Approach 1:
The patent applies asymmetry by making the enlarged portions in the first array of electrodes different in size from the enlarged portions in the second array of electrodes. Specifically, the first array (closer to the ground plane) has smaller enlarged portions while the second array has larger enlarged portions. This asymmetric configuration balances the signal maximization need with ground plane interference reduction, as the smaller enlarged portions in the first array trap fewer field lines that would otherwise be attracted to the ground plane, while the larger enlarged portions in the second array maintain sufficient signal strength.
Solution Approach 2:
The patent applies local quality by varying the fill factor and enlarged portion sizes at different locations within the electrode arrays. The first array of electrodes (closer to the ground plane) has a different fill factor and smaller enlarged portions compared to the second array (farther from the ground plane) which has a higher fill factor and larger enlarged portions. This localized variation optimizes the balance between signal strength and ground plane interference at each specific location within the touch sensor structure.
2Ease of manufacture
If symmetric enlarged portions are used in both arrays to simplify manufacturing, then the manufacturing complexity decreases, but the touch screen sensitivity is reduced due to uniform field distribution that does not account for ground plane interference
Solution Approach 1:
The patent deliberately introduces asymmetry in the enlarged portions between the two electrode arrays to improve touch screen sensitivity. The first array has smaller enlarged portions while the second array has larger enlarged portions, creating an asymmetric pattern that compensates for ground plane interference. This asymmetric design prioritizes measurement precision over manufacturing simplicity, as the different sizes can be fabricated using standard photolithography processes with appropriate mask design.
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 configuration improves touch screen sensitivity by maintaining consistent percentage capacitance change as the fill factor increases, reducing the influence of the ground plane and enhancing the accuracy of touch position detection.
Implementation Method 1
sensing the capacitance change induced between orthogonal sets of electrodes, or between a grounded stylus and individual electrodes
Implementation Method 2
one set of the orthogonal electrodes will be close to an electrical ground plane within the display itself. This tends to reduce the sensitivity, as the ground plane 'attracts' electric field lines that would otherwise extend out of the device
Data Source
Figure 1
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AI summary
A display device with touch sensor input has a touch sensor structure (16,18,20,22) having a first and second array of electrodes (18,22). The first and second arrays of electrodes occupy different fractions of a touch sensor area. These asymmetric fill factors give improved sensitivity.