Capacitive Touch Screen Water Rejection via Dual-Mode Detection
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Solution Overview
Problem
Capacitive touchscreen panels face challenges in distinguishing between user input and foreign matter like water, as both can alter capacitance readings, leading to false detection and reduced accuracy in touch recognition, especially in environments where both multi-touch detection and water rejection are required.
Innovation Solution
A method that performs touch detection in both mutual capacitance and self-capacitance modes, identifying coincident nodes, forming capacitance islands and expanded boundary layers, and calculating ratios to differentiate between valid touches and foreign matter by analyzing capacitance strengths and their distributions within and outside a self-capacitance window.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If capacitive touch detection is performed using mutual capacitance mode, then multi-touch detection capability is improved, but false detection of foreign matter like water increases
Solution Approach 1:
The patent segments the touch detection process into multiple modes (self-capacitance mode and mutual capacitance mode) and multiple processing stages (node identification, island formation, boundary layer creation, ratio calculation). By dividing the detection into distinct segments with different functions, the system can leverage the water-rejection advantage of self-capacitance mode while maintaining the multi-touch capability of mutual capacitance mode, thereby resolving the contradiction between versatility and reliability.
Solution Approach 2:
The patent introduces an intermediary processing mechanism that compares results from both self-capacitance mode and mutual capacitance mode. The system uses self-capacitance mode as an intermediary filter to identify potential foreign matter, then uses mutual capacitance mode for accurate multi-touch detection only in regions confirmed to be free of foreign matter. This intermediary comparison process enables the system to achieve both multi-touch capability and foreign matter rejection.
2Measurement precision
If foreign matter rejection algorithms are implemented, then detection accuracy is improved, but processing complexity increases
Solution Approach 1:
The patent segments the complex foreign matter rejection process into manageable stages: (1) node identification in self-capacitance mode, (2) coincidence detection between modes, (3) island formation based on threshold criteria, (4) boundary layer creation, and (5) ratio calculation. Each stage performs a specific function with simple logic, making the overall complex algorithm implementable and efficient.
Solution Approach 2:
The patent applies partial action by only performing full foreign matter rejection processing on regions where foreign matter is suspected (identified through self-capacitance mode). For regions confirmed free of foreign matter, the system skips complex processing and directly uses mutual capacitance mode results. This partial application of the complex algorithm reduces overall processing complexity while maintaining detection accuracy where needed.
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
This approach enhances the accuracy of touch detection by effectively rejecting foreign matter like water while maintaining multi-touch capability, improving the precision and reliability of touch recognition in capacitive touchscreen systems.
Implementation Method 1
The capacitive sensing panel evaluates changes in capacitance at each capacitive node to detect a user touch or hover
Implementation Method 2
performing touch detection in a mutual capacitance mode to identify mutual capacitance touched nodes
Implementation Method 3
performing touch detection in a self-capacitance mode, wherein self-capacitance mode touched nodes are identified
Data Source
AI summary
A method of foreign matter rejection for multi-touch capacitive touch screens includes performing touch detection in both self-capacitance mode and mutual capacitance mode. By combining information from both modes, a distinction is identified between wanted touches, such as by a finger or stylus, and unwanted touches such as by foreign matter.