In-Cell Touch Sensor Parasitic Capacitance Reduction
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Solution Overview
Problem
In in-cell touch sensor technology, the parasitic capacitance between touch sensors and gate lines leads to signal distortion due to RC delay, limiting the reduction of parasitic capacitance and affecting touch sensitivity and accuracy.
Innovation Solution
A display device with a time-division drive system that synchronizes display driving and touch sensor driving periods, using a modulator to generate modulation signals that minimize parasitic capacitance by supplying AC signals with the same phase and amplitude to data and gate lines during the touch sensor driving period, thereby reducing signal distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AC signal is supplied to gate lines during touch sensor driving period to reduce parasitic capacitance, then parasitic capacitance is reduced, but signal distortion occurs due to RC delay in low potential signal line
Solution Approach 1:
A buffer circuit is introduced as an intermediary component between the low potential input terminal and the low potential signal line. This buffer circuit includes a buffer transistor that isolates the AC signal from the parasitic capacitance of the low potential signal line, preventing RC delay distortion while maintaining the parasitic capacitance reduction effect. The buffer acts as a mediator that transfers the AC signal without allowing the signal line's parasitic capacitance to affect the waveform.
Solution Approach 2:
The patent replaces the direct electrical connection (which suffers from RC delay) with a buffer transistor-based signal transmission mechanism. Instead of allowing the AC signal to propagate directly through the capacitive-loaded low potential signal line, the buffer transistor actively drives the signal, substituting the passive RC network with an active buffer stage that maintains signal integrity.
2Adaptability or versatility
If segmented common electrode patterns are used as touch sensor electrodes, then in-cell touch sensor functionality is achieved, but parasitic capacitance between touch sensors and pixels increases
Solution Approach 1:
The common electrode is segmented into multiple patterns that serve dual functions as both pixel electrodes and touch sensor electrodes. This segmentation allows the touch sensor to utilize the existing pixel electrode structure, achieving in-cell integration without adding separate electrode layers. The segmented patterns are strategically designed to minimize overlapping areas and parasitic capacitance coupling between adjacent pixel and touch sensor elements.
Solution Approach 2:
The patent applies different structural characteristics to different regions of the electrode system. In regions where pixel and touch sensor electrodes overlap, the design optimizes the local geometry and spacing to minimize parasitic capacitance. The segmented common electrode patterns are configured with specific shapes and distributions that reduce capacitive coupling in critical areas while maintaining touch sensitivity and display performance.
3Ease of operation
If gate driver supplies AC signal through low potential signal line, then touch sensor driving is enabled, but waveform distortion occurs due to coupling with TFTs through parasitic capacitance
Solution Approach 1:
The buffer circuit serves as an intermediary stage between the gate driver's low potential input terminal and the low potential signal line that couples to TFTs. The buffer transistor isolates the AC signal from the parasitic capacitance of the signal line and TFT coupling, preventing waveform distortion while enabling touch sensor driving. This intermediary buffer stage maintains signal fidelity despite the capacitive loading of the downstream circuitry.
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 minimizes parasitic capacitance and signal distortion, enhancing touch sensitivity and accuracy by ensuring the AC signal applied to gate lines is in phase with the touch driving signal, thus improving the overall performance of in-cell touch sensors.
Implementation Method 1
A parasitic capacitance connected to the in-cell touch sensors increases due to coupling between the in-cell touch sensors and the pixels
Implementation Method 2
a waveform of the AC signal supplied to the output node is distorted by an influence of an RC delay
Data Source
AI summary
A display device comprising a display panel having touch sensors and gate lines, a touch sensor driver configured to supply a touch driving signal to the touch sensors of the display panel during a touch sensor driving period, a gate driver configured to supply a gate pulse synchronized with a data voltage of an input image to the gate lines of the display panel during a display driving period and supply an alternating current (AC) signal having a same phase as the touch driving signal to the gate lines during the touch sensor driving period, and a modulator configured to supply the AC signal having the same phase as the touch driving signal to the gate driver during the touch sensor driving period.