Pixelated Self-Capacitance Touch Sensing for Water Rejection

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Solution Overview

Problem

Capacitive touch sensor panels struggle to differentiate between water droplets and finger touch activity, leading to inaccurate touch recognition, especially when water droplets are isolated and not grounded.

Innovation Solution

Implement a comparison of fully bootstrapped and partially bootstrapped scans to identify the presence of water droplets on the touch screen, allowing them to be ignored or discarded from the touch image analysis.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If standard capacitive touch sensing is used, then touch detection capability is provided, but water droplets cannot be differentiated from finger touch activity

Engineering Contradiction:

Improvetouch detection accuracyVSAvoidtouch recognition accuracy

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent segments the touch sensing process into multiple scan types (fully bootstrapped scans and partially bootstrapped scans), allowing different sensing modes to be used for different purposes. Fully bootstrapped scans are used to detect water droplets, while partially bootstrapped scans are used for actual touch detection, thereby separating the detection of false signals from genuine touch events.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system uses feedback by comparing results from fully bootstrapped scans with partially bootstrapped scans. When water droplets are detected in the fully bootstrapped scan, the system adjusts the touch image analysis by ignoring those locations in the partially bootstrapped scan, improving overall touch recognition accuracy.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If fully bootstrapped scans are performed, then water droplets are detected, but processing time and computational resources increase

Engineering Contradiction:

Improvewater droplet detection accuracyVSAvoidscan processing time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent applies partial bootstrapping in certain scan regions or for certain touch nodes, rather than performing full bootstrapping across the entire touch screen. This allows water droplet detection capability to be maintained where needed while reducing the overall processing burden and time required for scanning.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The touch screen is divided into multiple scan regions or groups of touch nodes, and fully bootstrapped scans are performed selectively on specific regions rather than uniformly across the entire display. This segmentation reduces total processing time while maintaining water droplet detection capability in critical areas.

Inventive Principle:

Principle #1Segmentation

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 distinguishes between water droplets and finger touch activity, ensuring accurate touch recognition by ignoring water droplets and improving signal-to-noise ratio in touch sensing.

Implementation Method 1

Touch events can be sensed on the touch screens by detecting changes in the self-capacitance of the conductive plates (touch node electrodes)

Methodology Applied

Scientific EffectSelf-capacitance: Capacitance

Implementation Method 2

In some capacitive-type touch sensing systems, fringing electrical fields used to detect touch can extend beyond the surface of the display, and objects approaching near the surface may be detected near the surface without actually touching the surface

Methodology Applied

Scientific EffectFringing electrical fields: Electric Field

Data Source

PatentEP3213173B1Pixelated self-capacitance water rejection

Publication Date: 2025.10.29 APPLE INC

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AI summary

A touch sensor panel is disclosed. In some examples, the touch sensor panel comprises a plurality of touch node electrodes. In some examples, the touch sensor panel comprises a touch controller configured to drive and sense the plurality of touch node electrodes in a fully bootstrapped configuration to obtain a fully bootstrapped touch image, drive and sense the plurality of touch node electrodes in a second configuration, different from the fully bootstrapped configuration, to obtain a second touch image, the second touch image including an effect of water on the touch sensor panel, and determine a final touch image based on the fully bootstrapped touch image and the second touch image, the final touch image not including the effect of the water on the touch sensor panel. In some examples, the second configuration comprises a mutual capacitance configuration. In some examples, the second configuration comprises a partially bootstrapped configuration.