Touch Controller Guard Trace Noise Cancellation

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Solution Overview

Problem

As consumer electronic devices become thinner, the increasing parasitic capacitance between touch sensor panels and display panels generates significant noise interference, affecting the accuracy of touch or hover event recognition and potentially exceeding the operation range of touch sensing circuits.

Innovation Solution

A touch controller circuit design incorporating a reference voltage controlling circuit and a guard trace adjacent to the touch sensor panel, where a switch charges the guard trace to a reference voltage during a pre-charge period and opens it afterwards, utilizing the noise on the guard trace to cancel out noise interference in the sensing signal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If the distance between touch sensor panel and display panel is reduced to make devices thinner, then device thickness is reduced, but parasitic capacitance increases causing noise interference

Engineering Contradiction:

Improvedevice thicknessVSAvoidnoise interference

Core Design Contradiction:

Length of moving objectVSObject-affected harmful factors

Solution Approach 1:

A guard trace is introduced as an intermediary element between the touch sensor panel and display panel. The guard trace is coupled to the sensing circuit and positioned to intercept noise signals before they reach the sensing node, thereby mediating the harmful electromagnetic coupling while allowing the panels to remain in close proximity for thin device design

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The noise interference problem is extracted and handled separately by dedicating a specific circuit path through the guard trace. The sensing circuit is designed to process both the sensing signal and guard trace signal independently, then combine them to cancel noise, effectively separating the noise cancellation function from the basic sensing function

Inventive Principle:

Principle #2Taking out (Extraction)

2Length of moving object

If parasitic capacitance increases due to closer panel spacing, then device thickness decreases, but touch event recognition accuracy deteriorates

Engineering Contradiction:

Improvedevice thicknessVSAvoidtouch event recognition accuracy

Core Design Contradiction:

Length of moving objectVSMeasurement precision

Solution Approach 1:

The sensing circuit uses feedback by continuously monitoring the guard trace signal and using it to adjust the interpretation of the sensing node signal. The guard trace provides real-time noise information that feeds back into the sensing circuit to compensate for and cancel noise in the touch sensing measurements, maintaining accuracy despite increased parasitic capacitance

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The increased parasitic capacitance and associated noise, which would normally be purely harmful, are converted into a useful signal source. The guard trace captures the same noise that affects the sensing node, and this captured noise is then subtracted from the sensing signal, transforming the harmful noise coupling into a benefit for noise cancellation

Inventive Principle:

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

3Adaptability or versatility

If display panel changes screen frequently, then display functionality is improved, but noise coupling to touch sensor panel increases

Engineering Contradiction:

Improvedisplay functionalityVSAvoidnoise coupling

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The guard trace acts as a mediator that specifically targets and captures noise generated during display operations. By providing a dedicated path for noise signals and coupling it to the sensing circuit, the system can distinguish between actual touch signals and display-generated noise, allowing frequent screen changes without compromising touch sensing accuracy

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 design effectively reduces or cancels noise interference, improving the accuracy of touch event recognition and maintaining the voltage within the operational range of the touch sensing circuit.

Implementation Method 1

the parasitic capacitance between the two is getting larger. As a result, a great amount of noise will be generated and coupled to the touch sensor panel due to the large parasitic capacitance

Methodology Applied

Scientific EffectParasitic capacitance: Parasitic Capacitance

Data Source

PatentUS11620017B2Touch controllers capable of reducing noise interference

Publication Date: 2023.04.04 HIMAX TECH LTD

AI summary

A touch controller coupled to a touch sensor panel and arranged to detect touch events on the touch sensor panel includes a sensing circuit. The sensing circuit includes an integrator circuit and a reference voltage controlling circuit. The integrator circuit includes a first input node coupled to a sensing node for receiving a sensing signal, a second input node coupled to a guard trace disposed adjacent to the touch sensor panel and an output node outputting an integrated signal. The reference voltage controlling circuit includes a switch coupled between the second input node of the integrator circuit and a voltage source providing a reference voltage. The switch is closed during a pre-charge period to charge a voltage on the guard trace to the reference voltage in beginning of a sensing period and is opened after the pre-charge period.