Capacitive Touch Water Rejection via Self and Mutual Capacitance Scanning
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Solution Overview
Problem
Capacitive touch sensing systems face issues with accurate measurement and differentiation between touch events and water presence, leading to false touches and lost touches due to water's similar capacitance values, especially in wet conditions.
Innovation Solution
The implementation of a water rejection tool that uses self-capacitance and mutual-capacitance scanning to differentiate between water and touch events by comparing capacitance measurements to specific thresholds, adapting touch detection thresholds when water is detected, and employing a multiplexer circuit to connect capacitance-sensing circuits with sense arrays for effective water detection and touch recognition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitance sensing is used to detect touch events, then touch detection capability is improved, but false touches occur due to water's similar capacitance values
Solution Approach 1:
The patent segments the capacitance measurement into two distinct components: self-capacitance (measuring the capacitance of individual sense elements to ground) and mutual capacitance (measuring the capacitance between transmit and receive electrodes). By separating these measurements, the system can differentiate between water presence (which affects both similarly) and actual touches (which create distinctive mutual capacitance patterns), thereby reducing false touches while maintaining touch detection accuracy.
Solution Approach 2:
The patent dynamically changes measurement parameters by adjusting the type of capacitance measured (self vs. mutual) and modifying threshold values based on environmental conditions. The system adapts threshold parameters for touch detection based on baseline measurements taken under different conditions (dry vs. wet), allowing accurate touch detection while filtering out water-induced capacitance changes that do not match genuine touch patterns.
2Reliability
If water detection algorithms are implemented to reduce false touches, then false touch rejection is improved, but actual touches in wet conditions may be missed
Solution Approach 1:
The patent implements feedback mechanisms where the system continuously monitors capacitance measurements and adjusts detection thresholds based on observed patterns. Baseline measurements are taken and stored, and the system compares current measurements against these baselines while adapting thresholds dynamically. This feedback loop allows the system to learn environmental conditions (such as persistent wetness) and distinguish between water-induced changes and genuine touches, preventing both false rejections and missed detections.
Solution Approach 2:
The patent employs dynamic threshold adjustment where detection parameters are not fixed but adapt in real-time based on environmental conditions. The system modifies touch detection thresholds based on baseline measurements taken under current conditions (dry or wet), allowing the same hardware to operate accurately across varying environmental states. This dynamic adaptation ensures that water presence does not cause false rejections while maintaining sensitivity to actual touches.
3Reliability
If self-capacitance and mutual-capacitance scanning are used to differentiate water from touches, then water rejection capability is improved, but system complexity increases
Solution Approach 1:
The patent achieves multi-functionality by using the same sense array and basic capacitance sensing circuitry to perform multiple functions: detecting touches, detecting water presence, and differentiating between the two. The system uses the existing transmit and receive electrodes for both self-capacitance and mutual-capacitance measurements, eliminating the need for separate sensor arrays or specialized hardware. This universal use of existing components implements water rejection without proportionally increasing device 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
Enables accurate detection of touch events even in wet conditions by distinguishing water from actual touches, reducing false touch reports and ensuring reliable operation of capacitive touch sensing systems.
Implementation Method 1
The capacitive sense arrays work by measuring the capacitance of a capacitive sense element, and looking for a delta in capacitance indicating a touch or presence of a conductive object.
Implementation Method 2
employing a multiplexer circuit to connect capacitance-sensing circuits with sense arrays for effective water detection and touch recognition
Data Source
AI summary
A method, apparatus, and system to detect a self-capacitance activation in view of a self-capacitance measurement of a first electrode. The method, apparatus, and system further to detect a mutual capacitance activation in view of a mutual capacitance measurement of a pair of electrodes, and to determine the presence of water proximate to the capacitive button when the self-capacitance activation is false and the mutual capacitance activation is true. The capacitive button is disposed on a substrate.