Capacitive Touch Scanning Without Display Flicker

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional touchscreens experience display flickers due to parasitic capacitance between the touch panel and display panel, especially in thinner OLED designs, which interferes with display performance and causes noticeable dimming or flickering during touch sensing scans.

Innovation Solution

A touchscreen controller determines a sequence of excitation signals based on codes with alternating signs and absolute values, transmitting these signals simultaneously to touch sensors during a time frame to minimize interference with the display panel, and determines touch strengths from output signals received by receiving touch sensors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If the thickness of the stack above the display panel is reduced to improve brightness, then the brightness of the display is improved, but the coupling capacitance between the touch panel and display panel increases causing display flicker

Engineering Contradiction:

Improvedisplay brightnessVSAvoiddisplay flicker

Core Design Contradiction:

Illumination intensityVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful coupling capacitance effect into a beneficial one by using the parasitic capacitance between touch sensors and display panels as the sensing mechanism. The touch sensing system exploits the capacitive coupling that was previously causing flicker interference, transforming it into the basis for accurate touch detection while maintaining thin-stack design for brightness.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the operational parameters of the touch sensing system by using differential scanning methods and alternating current excitation signals. This allows the system to operate at frequencies and voltage levels that minimize interference with display refresh cycles, thereby reducing flicker while maintaining sensitivity.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If touch sensing scans are performed to detect touch, then touch detection functionality is provided, but display flicker occurs due to interference with control signals and image data

Engineering Contradiction:

Improvetouch detection functionalityVSAvoiddisplay flicker

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent segments the touch sensing operation into multiple phases: excitation phase, sensing phase, and reset phase. During the excitation phase, capacitive coupling is established; during the sensing phase, touch detection is performed; and during the reset phase, the system prepares for the next cycle. This segmentation allows coordination with display refresh timing to minimize flicker.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements periodic touch scanning synchronized with the display refresh rate. By performing touch scans at regular intervals that align with vertical blanking periods or specific phases of the display refresh cycle, the system minimizes interference with control signals and image data transmission, thereby reducing display flicker.

Inventive Principle:

Principle #19Periodic action

3Reliability

If a low impedance connection to power source is implemented for active matrix display, then display performance is improved, but the large power plane increases coupling capacitance with touch panel

Engineering Contradiction:

Improvedisplay performanceVSAvoidcoupling capacitance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces intermediary shielding structures and grounding planes between the touch panel and display power planes. These intermediary elements act as capacitive dividers and noise sinks, reducing the direct coupling capacitance between the high-current display power planes and the sensitive touch sensing electrodes, thereby reducing flicker while maintaining power delivery performance.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 reduces display flickers by canceling out voltage perturbations and allows for accurate touch strength determination, improving the operational stability of touchscreens without affecting display performance.

Implementation Method 1

coupling capacitance between a touch panel and the display panel

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS12008200B1Capacitive scan method without display flicker

Publication Date: 2024.06.11 STMICROELECTRONICS INT NV

AI summary

A method for operating a touch sensing panel includes a touchscreen controller determining a first plurality of excitation signals in accordance with a first plurality of codes, wherein a sum of the first plurality of codes is a sequence of numbers having a same absolute value and signs alternating between adjacent numbers in the sequence of numbers. The method further includes the touchscreen controller transmitting each of the first plurality of excitation signals to a respective transmitting (TX) touch sensor of the touch sensing panel simultaneously during a first time frame. The method further includes the touchscreen controller determining touch strengths in accordance with a first plurality of output signals received by a plurality of receiving (RX) touch sensors of the touch sensing panel during the first time frame.