Driven Shield Capacitive Touch Sensing for Liquid Interference
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Solution Overview
Problem
Capacitive touch detection systems face interference from liquids, leading to false positive touch detections due to cross-coupling effects between electrodes and ground, which reduces accuracy and reliability, especially in wet conditions.
Innovation Solution
Incorporating a driven shield that operates as a common transmitter for all electrodes, reducing cross-coupling effects and maintaining a higher touch detection threshold when liquid is present, while locking the touch interface to prevent false detections during water flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If liquid is present on the capacitive touch sensor surface, then electrical connection between sensors and ground components is established, but false positive touch detections occur and reliability deteriorates
Solution Approach 1:
A driven shield electrode is introduced as an intermediary component positioned between the touch sensors and ground components. The shield electrode is driven at a voltage that tracks the sensor voltage, creating an equipotential barrier that prevents liquid from establishing harmful electrical connections between sensors and ground, thereby eliminating false positives while maintaining reliable touch detection
Solution Approach 2:
The driven shield electrode is configured to be driven at a voltage that tracks or follows the voltage of the touch sensors. By maintaining equipotential conditions between the shield and sensors, the system eliminates potential differences that would otherwise drive current through liquid paths to ground, preventing false touch detections while preserving sensor functionality
2Measurement precision
If driven shield is driven to common voltage with electrodes, then cross coupling effects are reduced and measurement precision is improved, but device complexity increases
Solution Approach 1:
The driven shield electrode serves multiple functions simultaneously: it acts as a ground barrier to prevent liquid interference, a cross-coupling reduction element to improve measurement precision, and a voltage tracking reference. By consolidating these functions into a single component rather than using separate elements for each function, the patent reduces overall device complexity while achieving multiple benefits
3Reliability
If touch detection threshold is increased to reduce false positives, then reliability in wet conditions is improved, but sensitivity to legitimate touches may be reduced
Solution Approach 1:
The driven shield electrode is activated and configured to track sensor voltages before liquid interference can occur or before measurement takes place. By establishing the equipotential barrier in advance, the system prevents false positives from occurring rather than attempting to detect and correct them afterward, allowing normal sensitivity thresholds to be maintained while achieving high reliability in wet conditions
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 accuracy and reliability of touch detection by minimizing false positives and maintaining correct touch recognition even in the presence of liquids, improving the system's resilience to wet conditions.
Implementation Method 1
Capacitive touch detection techniques are used many touch driven devices... detects a tooth location based on measured changes in capacitance of the sensors
Implementation Method 2
liquid present on the surface of the capacitive touch sensor may establish an electrical connection between a first sensor and a second sensor
Data Source
AI summary
An apparatus includes a touch interface that includes a plurality of electrodes and a shield device. The shield device is configured to establish a first mutual capacitive coupling with a first electrode of the plurality of electrodes. The shield device is further configured to establish a second mutual capacitive coupling with a second electrode of the plurality of electrodes. The apparatus further includes a controller coupled to the touch interface. The controller is configured to detect a touch based on a detected first capacitance value of the first mutual capacitive coupling and a detected second capacitance value of the second mutual capacitive coupling.