Touch Sensing Circuit Noise Removal via Differential Amplifier

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Solution Overview

Problem

On-cell type touch screen panels are vulnerable to display noise due to increased parasitic capacitances between the touch screen substrate and the TFT substrate, which complicates the detection of touch inputs, especially in multi-touch scenarios.

Innovation Solution

A touch sensing circuit that utilizes a differential amplifier to detect variations in coupling capacitance between adjacent driving electrodes, processing differentiated signals to generate a detection signal that differentiates between touched and untouched areas, thereby reducing display noise and enabling effective multi-touch recognition.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of stationary object

If on-cell type touch screen panel structure is used to reduce panel thickness, then panel thickness is reduced, but display noise increases due to increased parasitic capacitances

Engineering Contradiction:

Improvepanel thicknessVSAvoiddisplay noise

Core Design Contradiction:

Length of stationary objectVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful parasitic capacitances into useful coupling capacitances by strategically positioning receiving electrodes at intersections with driving electrodes. The parasitic capacitances that previously caused noise are now harnessed as the primary sensing mechanism for touch detection, allowing the system to benefit from the proximity of substrates while mitigating noise through differential measurement techniques.

Inventive Principle:

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

Solution Approach 2:

The patent introduces coupling capacitances as intermediary elements between driving electrodes and receiving electrodes. These coupling capacitances serve as mediators that transfer touch input signals through the substrate gap, enabling signal transmission while the differential amplifier circuit acts as an intermediary processing stage that filters out noise by comparing adjacent electrode pairs.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Difficulty of detecting and measuring

If capacitance scheme is used to detect touch input, then touch detection capability is achieved, but measurement precision deteriorates in multi-touch scenarios due to coupled capacitance variations

Engineering Contradiction:

Improvetouch detection capabilityVSAvoidtouch position detection accuracy

Core Design Contradiction:

Difficulty of detecting and measuringVSMeasurement precision

Solution Approach 1:

The patent segments the touch detection function by dividing the electrode array into multiple independent driving electrodes, each paired with its own receiving electrode at intersections. This segmentation allows independent sensing at each intersection point, enabling precise multi-touch detection by processing each electrode pair separately through dedicated sensing channels, thereby maintaining measurement precision even when multiple touches occur simultaneously.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent replaces traditional mechanical or single-point capacitance measurement with a differential electrical measurement system. By using differential amplifiers to compare voltage changes between adjacent driving electrodes and their corresponding receiving electrodes, the system substitutes direct mechanical touch detection with an electrical differential measurement approach that is more robust against coupled capacitance variations and enables precise multi-touch recognition.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 solution effectively removes display noise and enhances the ability to sense touch inputs on on-cell type touch screen panels, allowing for reliable high-speed multi-touch operations even in large-size panels by comparing relative changes in coupling capacitance between adjacent lines.

Implementation Method 1

a capacitance type touch screen panel (TSP) is used to detect an input position on the TSP by generating a minute variation in instantaneous current through capacitance when a user touches his/her finger to a dielectric film formed on electrodes of the TSP

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

in each node where the plurality of driving electrodes 111a to 111n and the plurality of receiving electrodes 113a to 113n cross each other, a coupling capacitance Cc is formed

Methodology Applied

Scientific EffectCoupling capacitance: Capacitance

Data Source

PatentUS8841927B2Touch sensing circuit

Publication Date: 2014.09.23 SILICON WORKS CO LTD

AI summary

A touch sensing circuit detects a difference in variation of coupling capacitances between mutually adjacent driving electrodes through the use of a differential amplifier, and senses whether or not a touch is made on a touch screen panel, thereby being capable of removing display noise.