In-Cell Touch Sensing Voltage Holding for Crosstalk Reduction
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Solution Overview
Problem
In display devices with built-in self-capacitive touch panels, particularly in in-cell and hybrid in-cell types, it is challenging to simultaneously perform output and touch sensing due to parasitic capacitance issues, leading to crosstalk and incorrect touch detection, especially when multiple touch points occur or adjacent electrodes are affected.
Innovation Solution
A method where a current is supplied to touch electrodes until an average voltage reaches a predetermined reference voltage, and the touch voltages are held to compare with a slope voltage, determining touch events while the voltages are maintained, thereby reducing the impact of parasitic capacitance and adjacent electrode interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a relaxation oscillation type is used for self-capacitive touch sensing, then touch detection can be performed, but parasitic capacitance between touch electrodes causes crosstalk and makes it difficult to determine touch events accurately
Solution Approach 1:
The patent changes the voltage application parameters by applying different voltages to different touch electrodes during the sensing period. Specifically, it applies a first voltage to a first touch electrode and a second voltage (different from the first) to a second touch electrode, which eliminates the parasitic capacitance interference and enables accurate touch detection in in-cell type touch panels.
2Adaptability or versatility
If touch electrodes are used as common electrodes in self-capacitive type, then touch sensing can be performed, but output and touch sensing cannot be performed simultaneously
Solution Approach 1:
The patent implements periodic action by dividing the frame period into a display period and a touch sensing period. During the display period, video signals are output, and during the touch sensing period, touch sensing is performed by applying sensing voltages to touch electrodes. This periodic separation allows both functions to be performed in alternating intervals.
3Area of stationary object
If multiple sensors are needed for touch detection, then touch coverage is improved, but device complexity increases requiring multiple ICs
Solution Approach 1:
The patent applies multi-functionality by using the same touch electrodes to serve dual purposes: as common electrodes for liquid crystal driving during the display period and as sensing electrodes for touch detection during the touch sensing period. This eliminates the need for separate sensor ICs and reduces device complexity while maintaining comprehensive touch coverage.
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 touch detection accuracy by minimizing crosstalk and noise interference, allowing for precise determination of touch events without voltage distortion, thus improving touch sensitivity and signal-to-noise ratio.
Implementation Method 1
supplying a current to the touch electrodes, and when an average voltage of the touch electrodes reaches a predetermined reference voltage
Implementation Method 2
holding touch voltages of the respective touch electrodes when an average voltage of the touch electrodes reaches a predetermined reference voltage
Implementation Method 3
a parasitic capacitance is generated between self-capacitances in the in-cell touch panel, and thus, when the same voltage is not provided, the parasitic capacitance value is greatly changed
Data Source
AI summary
Discussed is a display device. The display device includes a panel in which a self-capacitive touch panel including a plurality of touch electrodes is built, and a touch sensing unit configured to, during a touch sensing period in one frame period, supply a current to the touch electrodes, hold touch voltages of the respective touch electrodes when an average voltage of the touch electrodes reaches a predetermined reference voltage, and compare each of the touch voltages with a slope voltage to determine whether each of the touch electrodes is touched while the touch voltages are being held.