Touch Sensing Feedback Clamping for Display Noise Cancellation

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Solution Overview

Problem

Touch panels in display systems face interference from underlying display systems due to large voltage pulses, causing saturation and impairing touch event detection.

Innovation Solution

Implementing a system with voltage clamping and correction mechanisms to manage overvoltage and undervoltage, using comparators and transistors to maintain circuit operation within safe thresholds, and employing auxiliary feedback systems to reduce interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If the touch panel is placed close to the display system, then the display area is maximized and the device is more compact, but electrical interference from the display system couples to the touch panel electrodes causing circuit saturation

Engineering Contradiction:

Improvedisplay areaVSAvoidelectrical interference

Core Design Contradiction:

Area of stationary objectVSObject-affected harmful factors

Solution Approach 1:

A noise cancellation circuit is introduced as an intermediary between the display system and the touch panel. This circuit includes a noise cancellation generator that produces noise signals matching the interference from the display system, and a noise cancellation driver that applies these signals to counteract the harmful electrical interference, allowing the touch panel to operate close to the display without saturation

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system employs feedback mechanisms where the noise cancellation generator continuously monitors the interference environment and adjusts the noise cancellation signals accordingly. The circuit uses feedback from the touch panel electrodes to dynamically adapt the noise cancellation driver's output, ensuring optimal interference cancellation while maintaining touch sensitivity

Inventive Principle:

Principle #23Feedback

2Power

If large voltage pulses are used to drive the display system, then the display performance is improved, but the coupled electrical interference saturates the touch sensor circuits

Engineering Contradiction:

Improvedisplay drive powerVSAvoidtouch detection reliability

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The invention converts the harmful electrical interference from the display system into a beneficial signal for noise cancellation. The noise cancellation generator captures the interference patterns produced by the display's large voltage pulses and uses these same patterns to generate counter-signal that cancels the interference, thereby allowing high-power display operation without compromising touch detection reliability

Inventive Principle:

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

3Speed

If the touch panel electrodes are driven at high frequency, then the touch response is improved, but the interference from the display system falls within the same frequency band making filtering difficult

Engineering Contradiction:

Improvetouch response speedVSAvoidinterference filtering difficulty

Core Design Contradiction:

SpeedVSDifficulty of detecting and measuring

Solution Approach 1:

The noise cancellation generator performs preliminary action by continuously generating and preparing noise cancellation signals that match the expected interference patterns. These pre-computed cancellation signals are ready to be applied immediately when interference occurs, allowing the system to maintain high-frequency touch operation without suffering from difficult-to-filter interference

Inventive Principle:

Principle #10Preliminary 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

Effectively reduces electrical interference, preserving touch sensing functionality by preventing circuit saturation and maintaining signal integrity.

Implementation Method 1

clamping the feedback voltage to an upper voltage threshold in response to the first voltage difference exceeding the upper voltage threshold, and clamping the feedback voltage to a lower voltage threshold in response to the first voltage difference being less than the lower voltage threshold

Methodology Applied

Scientific EffectVoltage clamping:

Implementation Method 2

a first threshold comparator configured to generate a first control signal in response to a first voltage difference between the feedback voltage and the reference voltage

Methodology Applied

Scientific EffectVoltage comparison:

Implementation Method 3

a first transistor configured to switch current flow in response to the first control signal, the first transistor having a first source connected to the feedback node, a first drain connected to the reference node, and a first gate connected to the first control signal

Methodology Applied

Scientific EffectTransistor switching:

Data Source

PatentUS12504850B2Methods and apparatus for display noise canceling in a touch sensing system

Publication Date: 2025.12.23 NXP BV

AI summary

A method for display noise canceling in a touch sensing system includes measuring a first feedback voltage of a feedback node resistively coupled to a line voltage of a capacitive touch panel, the line voltage formed by a continuous wave output of an amplifier responsive to a reference voltage difference between the first feedback voltage and a reference voltage. A second feedback voltage is clamped to a first upper voltage threshold in response to a first voltage difference between the first feedback voltage and the reference voltage being greater than the first upper voltage threshold. The second feedback voltage is clamped to a first lower voltage threshold in response to the first voltage difference being less than the first lower voltage threshold.