Differential Touch Sensing Circuit for High-Refresh Display Noise

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Solution Overview

Problem

High-speed driving, thinning, and enlargement of display devices lead to reduced touch sensing sensitivity due to increased parasitic capacitance and noise interference from display driving signals, affecting the performance of touch sensors.

Innovation Solution

An input sensing device with driving electrodes and sensing electrodes, featuring an analog front-end that differentially amplifies and filters signals using charge amplifiers and demodulation circuits, and a signal processor to enhance sensing sensitivity by reducing noise and parasitic capacitance effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If the display device is driven at high speed (increased from 60 Hz to 120 Hz), then the display performance is improved, but the touch sensing time is reduced and sensing sensitivity is degraded

Engineering Contradiction:

Improvedisplay driving speedVSAvoidtouch sensing sensitivity

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The patent segments the touch sensing process into multiple phases within each frame period, including a first sensing phase during the horizontal blanking period and a second sensing phase during the vertical blanking period. This segmentation allows touch sensing to occur at multiple time points, effectively increasing the total sensing time available despite the higher display refresh rate, thereby maintaining sensing sensitivity while achieving high-speed display performance.

Inventive Principle:

Principle #1Segmentation

2Volume of moving object

If the display device is thinned and enlarged, then the device form factor is improved, but the parasitic capacitance is increased and sensing sensitivity is degraded

Engineering Contradiction:

Improvedevice thickness and sizeVSAvoidtouch sensing sensitivity

Core Design Contradiction:

Volume of moving objectVSMeasurement precision

Solution Approach 1:

The patent introduces a compensation electrode as an intermediary element that is configured to receive the display driving signal and generate a compensation signal. This compensation electrode acts as a mediator between the display panel and the touch sensing electrodes, generating a signal that counteracts the parasitic capacitance effects caused by the thinned and enlarged structure, thereby maintaining sensing sensitivity despite the improved form factor.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Speed

If the display driving signal frequency is increased, then the display refresh rate is improved, but the noise interference to touch sensing is increased

Engineering Contradiction:

Improvedisplay refresh rateVSAvoidnoise interference

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful display driving signal into a beneficial compensation signal by using the same signal to drive the compensation electrode. The compensation electrode generates a signal that mirrors the display driving signal's noise characteristics but with opposite polarity, effectively canceling out the noise interference when combined with the touch sensing signal, thereby allowing high refresh rates without compromising touch sensing quality.

Inventive Principle:

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

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

The solution effectively increases touch sensing sensitivity and accuracy even in environments with deteriorated touch sensor performance, by filtering noise and minimizing parasitic capacitance, thus improving the reliability of touch input detection.

Implementation Method 1

a first charge amplifier configured to differentially amplify a first sensing signal and a second sensing signal provided from two sensing electrodes among the sensing electrodes to first and second input terminals, thus outputting a first differential signal and a second differential signal

Methodology Applied

Scientific EffectDifferential amplification:

Implementation Method 2

a first demodulation circuit configured to filter each of the first and second differential signals in a first mode, and to filter each of the third and fourth differential signals in a second mode

Methodology Applied

Scientific EffectSignal filtering: Filter (electronic)

Implementation Method 3

The touch panel may include a plurality of sensing electrodes, and may determine a touched point by sensing a change in capacitance formed on a plurality of touch electrodes

Methodology Applied

Scientific EffectCapacitance sensing: Capacitance

Data Source

PatentUS11543914B2Input sensing device and display device having the same

Publication Date: 2023.01.03 SAMSUNG DISPLAY CO LTD

AI summary

An input sensing device includes driving electrodes and sensing electrodes, and an analog front-end which processes sensing signals from the sensing electrodes to output a differential output value. The analog front-end includes a first charge amplifier which differentially amplifies first and second sensing signals from two sensing electrodes to first and second input terminals, thus outputting first and second differential signals through first and second output terminals, a second charge amplifier which differentially amplifies the first and second differential signals, thus outputting third and fourth differential signals, a first demodulation circuit which filters the first and second differential signals in a first mode and filters each of the third and fourth differential signals in a second mode, and a first analog-to-digital converter which outputs a first sensing value based on at least one output signal of the first demodulation circuit.