Shield Layer for Capacitive Touch Panel Parasitic Noise

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Solution Overview

Problem

Projection-type electrostatic capacitive touch panels face issues with detection performance due to parasitic capacitance from pressure sensors, leading to noise interference and reduced durability, especially when high dielectric materials like moisture adhere to the touch surface.

Innovation Solution

Incorporating a shield layer with conductive material between the touch surface and pressure sensor, and an insulating layer to electrically isolate the shield layer from the pressure sensor, which suppresses parasitic capacitance and enhances detection performance by reducing noise components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a pressure sensor is added to detect pressure from capacitance change, then pressure detection function is achieved, but parasitic capacitance increases causing noise and reducing detection performance

Engineering Contradiction:

Improvepressure detection functionVSAvoiddetection performance

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

A shield electrode is introduced as an intermediary component between the touch sensor and pressure sensor. This shield electrode acts as a mediator to block parasitic capacitance from affecting the pressure sensor's detection, allowing the pressure detection function to be added without degrading the detection performance of either sensor

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If piezoelectric element or film is used for pressure detection, then pressure detection is achieved, but contact and non-contact repetition reduces durability

Engineering Contradiction:

Improvepressure detection capabilityVSAvoiddurability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent replaces the mechanical contact-based piezoelectric pressure detection system with a capacitive pressure sensor that detects pressure through capacitance changes without physical contact. This substitution eliminates the wear caused by repeated contact and non-contact cycles, significantly improving durability while maintaining pressure detection capability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Object-affected harmful factors

If high dielectric material such as moisture adheres to touch surface, then waterproof property is maintained, but detection value reacts to high dielectric material causing erroneous touch detection

Engineering Contradiction:

Improvewaterproof propertyVSAvoidtouch detection accuracy

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The patent segments the detection functions into two independent systems: an electrostatic capacitive touch sensor for touch detection and a pressure sensor for pressure detection. By using the pressure sensor that is less sensitive to dielectric materials like moisture, the system can distinguish between actual touch events and moisture adhesion, maintaining both waterproof property and detection accuracy

Inventive Principle:

Principle #1Segmentation

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 configuration improves the detection accuracy and reliability of pressure sensors by minimizing parasitic capacitance, allowing for precise detection of touch coordinates and pressure without erroneous readings from adherent moisture, thus enhancing the overall performance and durability of the touch panel.

Implementation Method 1

when there is parasitic capacitance between a pressure sensor and a pointer or the like, the pressure sensor being capable of detecting pressure from a change in a capacitance, there is a problem that the parasitic capacitance becomes a noise component of the electrostatic capacitance detected by the pressure sensor

Methodology Applied

Scientific EffectParasitic capacitance: Parasitic Capacitance

Implementation Method 2

the electrostatic capacitance detection sensor capable of detecting a change in the electrostatic capacitance formed between the touch sensor panel and a pointer

Methodology Applied

Scientific EffectElectrostatic capacitance: Capacitance

Implementation Method 3

the pressure sensor capable of detecting pressure from a change in the capacitance caused by approaching of a conductor or a dielectric body to the sensor electrode

Methodology Applied

Scientific EffectElectrostatic capacitance: Capacitance

Data Source

PatentUS10852892B2Touch panel and display apparatus

Publication Date: 2020.12.01 MITSUBISHI ELECTRIC CORP

AI summary

A touch panel includes a touch sensor panel including a touch sensor capable of detecting a change in electrostatic capacitance formed between the touch sensor panel and a pointer, a pressure sensor capable of detecting a pressure on a touch surface of the touch sensor panel as a change in electrostatic capacitance, and a shield layer. The shield layer is disposed between the touch surface and the pressure sensor so as to be overlapped with at least a part of the pressure sensor as viewed from the touch surface.