PCAP Touchscreen Water Contamination Immunity via Dynamic Mode Switching
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Solution Overview
Problem
Projected capacitive (PCAP) touchscreens face significant performance degradation in the presence of water contaminants due to the conductivity and high dielectric constant of water, leading to compromised touch signal integrity and false touch reports, especially in mutual-mode operations.
Innovation Solution
Implementing a system that switches between self-mode and mutual-mode operations based on water contamination, using a mixed-mode measurement frame that simultaneously measures both self-mode and mutual-mode signals at varying frequencies to enhance touch detection accuracy and reliability, and employing a mode state machine to determine the optimal operational mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mutual-mode readout is used for PCAP touchscreen, then multi-touch performance is improved, but performance degrades rapidly with increasing water contaminants on the touch surface
Solution Approach 1:
The system dynamically switches between mutual-mode and self-mode readout operations based on detected water contamination levels. When water contaminants are detected above a threshold, the system transitions from mutual-mode to self-mode, and vice versa when contamination is below the threshold. This dynamic adaptation resolves the contradiction by selecting the appropriate operational mode for current environmental conditions.
Solution Approach 2:
The system changes the operational parameter (readout mode) from mutual-mode to self-mode based on water contamination levels. This parameter change allows the system to maintain reliable touch detection by using self-mode when water contaminants are present, as self-mode is less susceptible to water-induced signal degradation.
2Reliability
If self-mode readout is used for PCAP touchscreen, then resistance to water contaminants is improved, but multi-touch performance is reduced
Solution Approach 1:
The system dynamically switches between self-mode and mutual-mode readout operations based on detected water contamination levels. When water contaminants are detected above a threshold, the system transitions from mutual-mode to self-mode, and vice versa when contamination is below the threshold. This dynamic adaptation resolves the contradiction by selecting the appropriate operational mode for current environmental conditions.
Solution Approach 2:
The system changes the operational parameter (readout mode) from self-mode to mutual-mode based on water contamination levels. When water contaminants are below the threshold, the system uses mutual-mode to achieve superior multi-touch performance. This parameter change allows the system to optimize for multi-touch capability when environmental conditions permit.
3Device complexity
If a single readout mode is used, then system complexity is reduced, but adaptability to different environmental conditions is limited
Solution Approach 1:
The PCAP touchscreen system incorporates both mutual-mode and self-mode readout capabilities within a single device, enabling it to function effectively across diverse environmental conditions. The system includes a mode state machine that automatically selects the appropriate readout mode based on water contamination detection, providing universal adaptability without requiring multiple separate systems.
Solution Approach 2:
The system dynamically switches between mutual-mode and self-mode readout operations based on detected water contamination levels. When water contaminants are detected above a threshold, the system transitions from mutual-mode to self-mode, and vice versa when contamination is below the threshold. This dynamic adaptation resolves the contradiction by selecting the appropriate operational mode for current environmental 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
This approach maintains reliable touch performance and accuracy even in the presence of water contaminants by resolving ambiguities and reducing false touch reports, while optimizing signal processing to distinguish between touch signals and water-induced interference.
Implementation Method 1
Water is a troublesome contaminant for PCAP touchscreens that sense touches through electric field effects. The conductivity of water, as well as its very high relative dielectric constant of about 80, perturbs electric fields and hence can compromise PCAP touchscreen signals.
Implementation Method 2
The conductivity of water, as well as its very high relative dielectric constant of about 80, perturbs electric fields and hence can compromise PCAP touchscreen signals.
Data Source
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Figure 2A~2B
Figure 3A~3B
AI summary
System, method, and computer program product embodiments are provided that can support touch interaction on a projective capacitive (PCAP) display system in the presence of water contamination. According to an embodiment, a system includes a touchscreen coupled to a controller. The controller determines the presence of water contamination on the touchscreen, and obtains measurements during a mixed-mode measurement frame that includes a self-mode measurement and a mutual-mode measurement. Based on the measurements obtained, the controller determines a touch on the touchscreen in the presence of the water contamination on the touchscreen. In some embodiments, the self-mode measurement includes measurements collected at a both lower and a higher drive frequency, the higher drive frequency may be in the frequency range of 100kHz to 500kHz. In another embodiment, the self-mode measurement includes simultaneously measuring both horizontal-electrodes and vertical-electrodes.