Input Device Moisture Sensing with Out-of-Phase Electrode Drive
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Solution Overview
Problem
Capacitive sensor devices face difficulties in accurately detecting user input in humid environments due to the presence of moisture, which affects their functionality in determining the presence of input objects.
Innovation Solution
A method involving driving sets of electrodes with out-of-phase waveforms to destructively interfere, combined with absolute capacitance sensing, allows for the detection of moisture on the sensing region by analyzing grounding conditions and signal patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional capacitive sensing is used, then the device can detect user input, but it cannot distinguish between moisture and input objects in humid environments
Solution Approach 1:
The patent divides the electrode array into multiple groups that can be independently driven with different waveforms. By segmenting the sensing region and using separate waveform control for different electrode groups, the system can create distinct signal patterns that help differentiate between moisture and input objects based on their unique capacitive effects on the segmented regions.
Solution Approach 2:
The patent changes the waveform parameters (phase, frequency) applied to different electrode groups to create out-of-phase signals. This parameter variation allows the system to exploit the different capacitive coupling characteristics of moisture versus input objects, enabling the processing system to distinguish between the two based on how they modulate the out-of-phase signals.
2Reliability
If out-of-phase waveforms are used to destructively interfere, then signal interference is reduced, but device complexity increases
Solution Approach 1:
The patent implements a waveform generation system that can produce multiple different waveforms (including out-of-phase combinations) using a unified control architecture. The same processing system that manages normal capacitive sensing also controls the out-of-phase waveform generation, allowing the system to reuse existing hardware resources for interference cancellation without adding separate dedicated complexity.
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
Enhances the ability of capacitive sensors to differentiate between moisture and input objects, improving touch performance in humid conditions by accurately determining the presence of moisture and maintaining functionality.
Implementation Method 1
the first waveform and the second waveform are out of phase with each other such that the first waveform destructively interferes with the second waveform
Implementation Method 2
Capacitive sensor devices may include a sensing region, often demarked by a surface (e.g., display screen), in which the capacitive sensor device determines the presence, location and/or motion of one or more input objects
Data Source
AI summary
A method for capacitive sensing is provided. The method comprises driving a first set of electrodes using a first waveform and a second set of electrodes using a second waveform. The first waveform and the second waveform are out of phase with each other such that the first waveform destructively interferes with the second waveform. The method further includes obtaining, using the first set of electrodes, first resulting signals based on driving the first set of electrodes and the second set of electrodes; obtaining second resulting signals based on operating a third set of electrodes from the plurality of electrodes in an absolute capacitance sensing (ABS) scheme; and determining a presence of moisture on a sensing region of the input device based on the first resulting signals and the second resulting signals.