Optical Sensor Ambient Light Filter for Fingerprint Imaging
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Solution Overview
Problem
Traditional optical fingerprint sensors are susceptible to noise from ambient light, leading to variable image quality and requiring a large dynamic range, especially under intense lighting conditions, which makes them unsuitable for small form factor devices.
Innovation Solution
Incorporating an ambient light filter between the display layer and the image sensor layer to selectively block or attenuate ambient light, maintaining a consistent dynamic range and reducing sensitivity to ambient conditions while preserving the desired light signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional optical fingerprint sensors are used without ambient light filters, then the device structure remains simple, but the sensor is susceptible to noise from ambient light causing variable image quality and requiring large dynamic range
Solution Approach 1:
An ambient light filter layer is introduced as an intermediary component between the display layer and image sensor layer. This filter selectively blocks ambient light wavelengths while allowing the desired light signal to pass through, thereby improving image quality consistency without fundamentally changing the sensor's core structure
Solution Approach 2:
The ambient light filter is positioned specifically between the display layer and image sensor layer, applying wavelength-selective filtering only where needed. This localized approach addresses the ambient light interference problem while maintaining simplicity in other parts of the device structure
2Reliability
If ambient light filters are added to block ambient light, then image quality and dynamic range consistency improve, but the device structure becomes more complex
Solution Approach 1:
The ambient light filter functionality is merged with existing device layers. The filter is integrated between the display layer and image sensor layer, combining the filtering function with the existing optical path structure rather than adding a completely separate subsystem
Solution Approach 2:
The filter modifies the optical parameters by selectively blocking specific wavelength ranges of ambient light while maintaining transmission of the desired light signal. This parameter-based filtering approach achieves dynamic range consistency through optical property modification rather than complex electronic control
3Area of stationary object
If the sensor is made smaller for compact devices, then the form factor improves, but the sensor becomes more susceptible to ambient light noise
Solution Approach 1:
The ambient light filter serves as a protective intermediary that shields the compact image sensor from ambient light interference. This allows the sensor to maintain a small area while the filter handles the ambient light rejection function
Solution Approach 2:
The filter applies wavelength-selective blocking specifically at the sensor's input surface, providing targeted protection against ambient light without requiring the sensor itself to be larger or more complex
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 ambient light filter significantly reduces the intensity of ambient light reaching the image sensor, maintaining a consistent dynamic range and improving image quality by ensuring the desired light signal intensity is maintained, as demonstrated by a 9× brighter reflected light from the illumination source compared to 15× brighter ambient light without the filter.
Implementation Method 1
a first ambient light filter layer, disposed between the display layer and the image sensor layer, configured to block one or more wavelengths of light
Data Source
AI summary
An optical sensor device includes: a display layer, comprising a light source configured to generate light incident on an input surface of the optical sensor device; an image sensor layer, disposed below the display layer, comprising an optical image sensor having a plurality of image sensor pixels; and a first ambient light filter layer, disposed between the display layer and the image sensor layer, configured to block one or more wavelengths of light.