In-Cell Touch Sensing Compensation for Display Crosstalk Noise
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Solution Overview
Problem
In in-cell touch type LCD devices, display and touch sensing functions are affected by each other due to structural characteristics, leading to display touch crosstalk (DTX) that causes noise and incorrect touch detection, even when no user is touching the screen.
Innovation Solution
A display device with a timing controller that alternately drives display and touch modes within a frame period, using compensation areas and differential touch (DTX) compensation values to correct for errors caused by grayscale changes in touch sensing blocks, thereby reducing DTX noise and improving touch sensing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If touch sensors are built in the liquid crystal panel, then the device can be slimmed down and display/touch functions are integrated, but display function and touch sensing function affect each other causing display touch crosstalk (DTX) noise
Solution Approach 1:
The patent divides the touch sensing area into multiple touch sensing blocks, each corresponding to multiple pixels. By segmenting the sensing function into discrete blocks and assigning dedicated sensing electrodes to each block, the system can independently compensate for DTX noise in each block based on its corresponding pixel's grayscale value, thereby reducing the overall impact of display-touch crosstalk while maintaining the integrated in-cell structure.
Solution Approach 2:
The patent dynamically adjusts the touch sensing threshold based on the grayscale value of the corresponding display pixel. When the pixel displays different brightness levels (grayscale changes), the sensing threshold is modified to compensate for the resulting capacitance variations. This parameter adaptation eliminates DTX noise caused by display content changes while preserving the slim integrated design.
2Device complexity
If common electrodes are used for both display and touch sensing functions, then device complexity is reduced, but touch sensing accuracy deteriorates due to DTX noise from grayscale changes
Solution Approach 1:
The patent implements multi-functionality by using the same common electrode for both display driving and touch sensing functions. During display mode, the common electrode serves as the display common electrode; during touch sensing mode, it becomes the touch sensing electrode. This universal usage reduces device complexity while the added compensation mechanism maintains sensing accuracy by correcting DTX noise.
Solution Approach 2:
The patent compensates for touch sensing accuracy degradation by dynamically adjusting the sensing threshold parameter based on the grayscale value of the corresponding pixel. This parameter change compensates for the capacitance variations caused by different display brightness levels, thereby maintaining high touch sensing accuracy despite using the same electrode for both functions.
3Adaptability or versatility
If touch sensing is performed during display operation, then user interaction is enabled, but DTX noise causes incorrect touch detection even when no user is touching the screen
Solution Approach 1:
The patent performs preliminary compensation by calculating the DTX noise value based on the pixel's grayscale value before conducting touch detection. The compensation value is pre-computed from the display content characteristics, and this preliminary compensation action is applied to the raw touch sensing signal, thereby eliminating false touch detections caused by display content while enabling reliable touch functionality.
Solution Approach 2:
The patent implements a feedback mechanism where the touch sensing threshold is dynamically adjusted based on the grayscale value of the corresponding pixel. The system continuously monitors the display content (grayscale) and feeds this information back to adjust the sensing threshold, thereby compensating for DTX noise and maintaining high touch detection reliability during display operation.
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 solution effectively reduces DTX noise, enhancing the touch sensing rate and accuracy by compensating for errors in touch data, ensuring correct detection of user input even during display operations.
Implementation Method 1
when a capacitance is changed in a touch sensing block touched by a user's finger, a touch sensing electrode senses the changed capacitance
Implementation Method 2
a pixel 'Black' displaying black and a pixel 'White' displaying white differ in alignment of liquid crystal, and thus, a difference between capacitances of a liquid crystal layer occurs
Data Source
AI summary
A display device comprises a timing controller and a touch sensing unit. The timing controller drives a display panel such that a display mode for displaying an image in the display panel and a touch mode for sensing a user' s touch are alternately driven. The touch sensing unit differentially applies DTX (display touch crosstalk) compensation values by compensation area to sense the user' s touch in the touch mode, each of touch sensing block being a sensing unit for a user' s touch. Each compensation area is set based on a distance between a data driver and the compensation area. Each DTX compensation value is a value for compensating for an error of touch data caused by changes in respective grayscale values applied to pixels corresponding to a specific touch sensing block. The touch sensing blocks are divided in a column direction depending on arrangement of multiplexers in the data driver.