Capacitive Touch Noise Reduction via Segmented Electrode Rows

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Solution Overview

Problem

As electronic devices become thinner, parasitic capacitance from the display interferes with touch screen sensors, causing noise that can saturate the system and lead to inaccurate readings, especially in flexible and extremely thin displays with reduced spacing between display and touch sensor electrodes.

Innovation Solution

A touch sensor array with additional circuitry, including current to voltage amplifiers and differential amplifiers, is used to detect and reduce parasitic capacitance by activating a noise detection and reduction row, which is separate from the rows used for touch detection, allowing for the subtraction of noise from receiver channel outputs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If the display and touch sensor array are placed closer together to enable thinner devices, then the device thickness is reduced, but parasitic capacitance from the display increases causing noise that interferes with touch detection

Engineering Contradiction:

Improvedevice thicknessVSAvoidparasitic capacitance noise

Core Design Contradiction:

Length of moving objectVSObject-affected harmful factors

Solution Approach 1:

The touch sensor array is divided into two separate functional rows: a first row dedicated to touch detection and a second row dedicated to noise detection. This segmentation allows the system to separately measure and subtract parasitic capacitance from the display, resolving the interference problem while maintaining thin device design.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A second row of electrodes acts as an intermediary noise detection channel that measures parasitic capacitance from the display without being used for primary touch detection. This intermediary row provides noise measurements that are subtracted from the first row's signals, eliminating the harmful parasitic capacitance effect.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If additional circuitry is added to detect and reduce noise, then noise reduction capability is improved, but device complexity increases

Engineering Contradiction:

Improvenoise reduction capabilityVSAvoidcircuitry complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The noise detection and reduction functions are merged into the existing touch sensor array structure by adding a second row of electrodes that shares the same readout circuitry. This combining approach provides effective noise reduction while minimizing additional complexity compared to separate detection systems.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The second row of electrodes serves multiple functions: it detects parasitic capacitance from the display, provides noise measurements for subtraction, and can potentially be used for additional touch detection zones. This multi-functionality reduces overall system complexity while improving noise reduction capability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 reduces noise, improving the signal-to-noise ratio and enabling the production of extremely thin, flexible displays by isolating and compensating for common mode noise, thereby enhancing the sensitivity and accuracy of touch screen interactions.

Implementation Method 1

The display projects parasitic capacitance to the touch sensor array. The parasitic capacitance is consistent across the array, such that it is common to each of the rows and columns of electrodes of the array.

Methodology Applied

Scientific EffectParasitic capacitance: Parasitic Capacitance

Implementation Method 2

The circuitry includes a plurality of first current to voltage amplifiers, each one of the plurality of first current to voltage amplifiers is coupled to one the plurality of columns.

Methodology Applied

Scientific EffectCurrent to voltage conversion:

Implementation Method 3

The circuitry includes a plurality of differential amplifiers, each one of the plurality of differential amplifiers is coupled to one of the plurality of first current to voltage amplifiers.

Methodology Applied

Scientific EffectDifferential amplification:

Data Source

PatentUS10599276B2Common mode noise reduction in capacitive touch sensing

Publication Date: 2020.03.24 STMICROELECTRONICS INT NV

AI summary

The present disclosure is directed to a system and method to remove common mode noise projected onto a touch sensor array from a display. The system is configured to activate two rows of electrodes at the same time, while coupling remaining rows of electrodes to ground. A first one of the two activated rows is used for detection of a touch and a second one of the two activated rows is used to detect common mode noise from the display. The common mode noise detected by the second row is removed from signals received from a plurality of columns of the touch sensor array.