In-cell Touch Screen Driving Method for Parasitic Capacitor Neutralization
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Solution Overview
Problem
Conventional in-cell touch screens are affected by parasitic capacitors, which reduce their sensitivity due to the additional load they form, making it necessary to develop a method that minimizes the impact of these capacitors on touch sensing.
Innovation Solution
The touch screen's common voltage layer is divided into sensing points, with source lines underlying a current VCOM electrode divided into groups, where a first voltage is applied during the conversion phase, and a second voltage is applied in specific patterns across these groups to ensure no net charge is contributed by parasitic capacitors during sensing periods, effectively neutralizing their impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If conventional in-cell touch screen structure is used, then the screen can be made thinner, but parasitic capacitors form a large load that reduces touch sensitivity
Solution Approach 1:
The source lines are divided into multiple groups (first group, second group, etc.), and voltages are applied to different groups in different sensing periods. This segmentation allows selective activation of parasitic capacitor groups, enabling the system to measure and compensate for parasitic effects while maintaining thin screen structure.
Solution Approach 2:
The patent changes the voltage parameters applied to source lines in different sensing periods. By applying different voltages (first voltage in one period, second voltage in another period) to different source line groups, the system can differentiate between parasitic capacitor effects and actual touch signals, thereby improving touch sensitivity despite the presence of parasitic capacitors.
2Device complexity
If parasitic capacitors are present in the in-cell structure, then the screen maintains its integrated design, but the parasitic capacitors create additional load that affects sensing accuracy
Solution Approach 1:
The patent converts the harmful effect of parasitic capacitors into a beneficial measurement tool. By applying voltages to different source line groups in different sensing periods and measuring the resulting currents, the system can calculate parasitic capacitance values and use this information to compensate for parasitic effects in actual touch measurements, thereby improving sensing accuracy while maintaining the integrated in-cell structure.
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 approach enhances the sensitivity of the touch screen by eliminating the effect of parasitic capacitors, resulting in improved touch sensing performance without altering the screen's structure or adding layers.
Implementation Method 1
A capacitor-based touch panel is a commonly used touch panel that utilizes capacitive coupling effect to detect touch position. Specifically, capacitance corresponding to the touch position changes and is thus detected, when a finger touches a surface of the touch panel.
Implementation Method 2
Conventional in-cell touch screens, however, possesses substantive parasitic capacitors that form a large load, thereby affecting sensitivity of the touch screen.
Data Source
AI summary
The present invention is directed to a method of driving an in-cell touch screen. Source lines underlying a current VCOM electrode are divided into n groups. A first voltage is applied at the current VCOM electrode in a conversion phase of each sensing period. A second voltage is applied at each group of the source lines underlying the current VCOM electrode in a manner such that no net charge being contributed to the VCOM electrode by the underlying source lines, thereby parasitic capacitors associated with the current VCOM electrode having no effect on touch sensing result.