Touch Sensor Guard Conductor Water Rejection
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Solution Overview
Problem
Touch sensor panels often incorrectly detect water droplets near the edges as intentional touches due to parasitic capacitive paths to ground, leading to unintended device behavior and user experience issues, especially in wet environments.
Innovation Solution
Incorporating conductors near the device housing that are driven with a stimulation signal to shield objects from capacitive coupling to ground, and employing scanning techniques such as non-bootstrapped and bootstrapped scans to differentiate between genuine touches and false ones caused by water droplets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If touch sensor panels use capacitive sensing to detect touches, then touch detection capability is improved, but water droplets near edges are falsely detected as touches due to parasitic capacitive paths to ground
Solution Approach 1:
A guard conductor is introduced as an intermediary element positioned between the water droplet and the grounded housing. This guard conductor is driven with a stimulation signal that creates an electric field to counteract the parasitic capacitive coupling path to ground, thereby preventing water droplets from being falsely detected as touches while maintaining genuine touch detection capability
Solution Approach 2:
The electrical potential of the guard conductor is dynamically changed by driving it with a stimulation signal that matches the characteristics of the touch sensor stimulation signal. This parameter change in the guard conductor's potential creates an equipotential region that eliminates the voltage difference necessary for parasitic capacitive coupling to ground, thus preventing false touch detection from water droplets
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 the likelihood of water droplets being misinterpreted as intentional inputs, enhancing the accuracy of touch detection and user experience by minimizing false touch registrations.
Implementation Method 1
water droplets that are capacitively coupled to ground via the housing or other conductive structures within a device can appear as a touch
Implementation Method 2
one or more conductors can be located in proximity to the housing and driven with a stimulation signal to shield objects from being capacitively coupled to ground through the housing
Data Source
AI summary
Techniques for rejecting apparent (but false) touches caused by objects such as water droplets located in areas with parasitic capacitive paths to ground are disclosed. To minimize these false touches, one or more guard conductors can be located in proximity to the housing and driven with a stimulation signal to shield objects from being capacitively coupled to ground through the housing. In some examples images of touch can be obtained from a non-bootstrapped or bootstrapped scan and also an extended bootstrapped scan wherein the guard conductor is driven with a stimulation signal that has the same characteristics as the stimulation signal being applied to the sensed touch nodes. In some examples, the results of the extended bootstrapped scan can be subtracted from the non-bootstrapped or bootstrapped scan to identify and reject apparent touches resulting from capacitive coupling to ground.