Touch Display Device Parasitic Capacitance Noise Removal

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Solution Overview

Problem

Conventional touch display devices suffer from poor performance in touch position sensing and fingerprint sensing, particularly due to interference from parasitic capacitance between data lines and fingers or fingerprints, which affects accuracy and freedom of design.

Innovation Solution

A touch display device with a display panel featuring pixel electrodes and transistors controlled by gate signals, utilizing a touch-sensing circuit that supplies driving signals and receives signals through data lines during different gate line states to isolate and remove parasitic capacitance, thereby improving sensing accuracy by using both capacitive and optical methods.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a separate fingerprint-sensing area is used, then fingerprint sensing can be performed, but freedom of design is inhibited and sensing performance is poor

Engineering Contradiction:

Improvefingerprint sensing performanceVSAvoidfreedom of design

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent merges the fingerprint sensing function with the image display area by using the same pixel electrodes and data lines for both display and sensing purposes. The pixel electrodes serve dual functions: displaying images and sensing fingerprint capacitance variations, eliminating the need for separate sensing areas and improving design freedom while maintaining sensing performance.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The data lines and pixel electrodes are designed to perform multiple functions: they serve as signal transmission lines for display and simultaneously as sensing elements for fingerprint detection. This multi-functionality allows the system to achieve both high-resolution display and accurate fingerprint sensing without requiring additional dedicated components.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Ease of operation

If conventional touch sensing is used, then touch input is provided, but parasitic capacitance between data lines and fingers degrades sensing accuracy

Engineering Contradiction:

Improvetouch input functionalityVSAvoidtouch position sensing accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent extracts and separately measures the parasitic capacitance component by utilizing the off-state of the transistor. When the transistor is turned off, the measured capacitance represents only the parasitic capacitance between the data line and finger. This extracted parasitic capacitance value is then subtracted from the total measured capacitance to obtain the accurate touch-related capacitance variation.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The system implements a feedback mechanism where the measured parasitic capacitance is used to compensate for sensing errors. By continuously monitoring and subtracting the parasitic capacitance component from the total capacitance measurement, the system dynamically corrects for the degradation caused by parasitic effects, thereby maintaining high sensing accuracy.

Inventive Principle:

Principle #23Feedback

3Device complexity

If data lines are used for both display and sensing, then device complexity is reduced, but parasitic capacitance interference increases

Engineering Contradiction:

Improvecircuit structure simplicityVSAvoidparasitic capacitance interference

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The patent employs periodic switching of the transistor between on and off states to separately measure different capacitance components. During the off-state period, parasitic capacitance is measured; during the on-state period, total capacitance including touch information is measured. This periodic action allows the system to distinguish and eliminate parasitic interference while using the same data lines for both display and sensing functions.

Inventive Principle:

Principle #19Periodic action

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

Enhances the accuracy of touch position and fingerprint sensing by eliminating noise components from parasitic capacitance, allowing for seamless integration of touch functionality within the image display area without separate sensing regions, thus improving user convenience and performance.

Implementation Method 1

a common electrode arranged corresponding to all the pixel areas and having a capacitance different according to a touch or a fingerprint

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

sense a touch position or a fingerprint by an optical method

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Data Source

PatentUS10488965B2Touch display device, display panel, touch-sensing method, touch-sensing circuit, and driving circuit

Publication Date: 2019.11.26 LG DISPLAY CO LTD

AI summary

A touch display device, a display panel, a touch-sensing method, a touch-sensing circuit, and a driving circuit, are discussed, which can detect a signal utilizing a pixel electrode and can remove a noise component that may be generated at the time of touch position sensing or fingerprint sensing while sensing a touch position or a fingerprint based on the detected signal, thereby improving sensing performance.