Optical Touch Display Angular Filtering Against Moisture False Detection
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Solution Overview
Problem
Optical touch sensing in electronic devices is challenged by false detection due to light reflection or refraction at the boundary between the detection surface and moisture, such as air, water, or other liquids, leading to inaccurate touch detection.
Innovation Solution
Employing light illuminator and detector angular filters within LED and photodiode components to limit illumination and detection angles, respectively, and forming inner and outer masks at the photodiode component level to block or filter light transmitted, reflected, or refracted within the cover material, thereby reducing false detection of water droplets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical touch sensing is employed to detect finger contact, then touch detection capability is improved, but false detection occurs due to light reflection and refraction at the boundary between detection surface and moisture
Solution Approach 1:
The patent introduces an angular filter as an intermediary component between the light source and photodiode. This filter selectively transmits light within a specific angular range while blocking light from other angles, thereby preventing false detection from moisture-induced reflections while maintaining accurate finger touch detection.
Solution Approach 2:
The patent changes the angular parameter of light transmission by implementing an angular filter that only allows light within a specific angular range to pass through. This parameter change enables the system to distinguish between valid touch signals and false signals from moisture by exploiting the angular characteristics of reflected versus scattered light.
2Reliability
If angular filters are implemented at the photodiode component level, then false detection of water droplets is reduced, but device complexity increases due to additional mask formation processes
Solution Approach 1:
The patent merges the angular filter formation process with the existing photodiode component fabrication process. By integrating the mask formation into the component-level manufacturing rather than adding a separate display assembly step, the overall device complexity is minimized while achieving the desired moisture detection accuracy.
Solution Approach 2:
The angular filter masks are formed in advance during the photodiode component manufacturing process, before the components are assembled into the final display device. This preliminary action allows for precise control of the angular filtering characteristics at the component level, simplifying the overall manufacturing process.
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
The solution effectively minimizes false detection of water droplets on the touch surface by isolating the mask formation process from display assembly, allowing for smaller and more accurately formed baffles and masks, thus enhancing the reliability of optical touch sensing in moist environments.
Implementation Method 1
an array of photodiodes (which may share a substrate with the array of image pixels) can be provided behind the cover material and can be configured to detect contact of an object with the display surface
Implementation Method 2
one or more light sources can be provided behind the cover material, such as an array of light emitting diodes (LEDs)
Implementation Method 3
light impinging on the boundary between the detection surface and a medium (e.g., air, water, or other liquid or moisture) above the detection surface can reflect off the boundary
Implementation Method 4
light impinging on the boundary between the detection surface and a medium (e.g., air, water, or other liquid or moisture) above the detection surface can reflect off the boundary, or refract as it passes through the boundary
Data Source
AI summary
An electronic device may have a touch sensitive display with optical touch sensors that are insensitive to the presence of moisture. The optical touch sensors may include light sources and light detectors. Light illuminator and detector angular filters (e.g., masks, baffles) can be employed to limit the illumination and receive angles of emitted and detected light to minimize false object detection. In some examples, light illuminator and detector masks and baffles can be formed during the photodiode component fabrication process. Interference filters may be included over the light sources and/or the light detectors to improve discrimination between a user's finger and water, and may have a greater transmission for light at a first incident angle that is greater than the critical angle of the water/cover interface than at a second incident angle that is less than the critical angle.