Through-Display Fingerprint Imaging Using Total Internal Reflection
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Solution Overview
Problem
Existing fingerprint detection systems face challenges in bezel-less or small bezel devices due to insufficient space for components, sensitivity to distance in capacitive sensing, noise issues in ultrasonic sensing, and bulkiness and cost of lensed digital cameras, making it difficult to scale across the computing device front face.
Innovation Solution
An imaging system utilizing a pixelated photoemitting and photodetecting element array that emits light through a display's cover glass, captures reflected light via total internal reflection, and stitches the captured light into a composite image using image processing circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If capacitive sensing components are positioned beneath the display, then the display area can be maximized, but the sensing resolution is dramatically reduced due to sensitivity to distance and cover glass interference
Solution Approach 1:
The patent replaces capacitive sensing (which relies on electrical fields and is sensitive to distance) with optical sensing using photodetectors and light sources. This substitution allows the sensing system to operate effectively through the cover glass without the distance sensitivity issues that plague capacitive sensing, thereby maintaining both full display area and high sensing resolution.
Solution Approach 2:
The patent introduces light as an intermediary medium to transmit fingerprint information from the finger surface to the photodetectors. By using optical waves that can penetrate the cover glass, the system overcomes the barrier effect of the glass and achieves high-resolution sensing without compromising display area.
2Ease of operation
If ultrasonic sensing is used for fingerprint detection, then contactless sensing is enabled, but noise issues and manufacturing issues arise due to detrimental mechanical impedance between the sensor and display surface
Solution Approach 1:
The patent replaces ultrasonic sensing (which uses mechanical waves and suffers from impedance mismatch with glass) with optical sensing. Light waves interact with the finger surface and transmit through the cover glass without the mechanical impedance issues that cause noise and manufacturing problems in ultrasonic systems.
3Measurement precision
If lensed digital cameras are used for fingerprint detection, then imaging capability is improved, but the device becomes bulky and expensive
Solution Approach 1:
The patent extracts the essential imaging function from complex lensed camera systems and implements it using simple photodetector arrays that directly capture optical information. By removing the bulky lens components and using planar photodetector sensors, the system achieves fingerprint imaging capability while dramatically reducing device complexity, thickness, and cost.
Solution Approach 2:
The patent creates an optical copy of the fingerprint surface by capturing reflected or transmitted light patterns with photodetectors. This optical copying method achieves high-resolution fingerprint imaging without requiring the complex optical paths and large lenses of traditional digital cameras.
4Measurement precision
If fingerprint detection components are placed outside the display area, then sensing resolution is maintained, but the display area is reduced due to bezel requirements
Solution Approach 1:
The patent merges the display function and fingerprint sensing function into a single integrated structure. Photodetectors and light sources are embedded within the display layers, allowing the same area to serve both as display and as fingerprint sensing region, thereby eliminating the need for separate sensing areas or larger bezels.
Solution Approach 2:
The patent makes the display area multi-functional by enabling it to simultaneously serve as both the visual display interface and the fingerprint detection interface. The photodetector array embedded in the display allows the display region itself to perform sensing functions, achieving universal use of the front surface area.
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
Enables effective fingerprint detection in bezel-less devices by providing both photodetecting and photoemitting functionality without increasing thickness, while overcoming sensitivity and noise issues, and allowing for scalable implementation.
Implementation Method 1
A portion of emitted light from one or more selected photoemitting elements of a pixelated photoemitting element array of the display
Implementation Method 2
The reflected light signal includes a portion of the emitted light signal reflected by total internal reflection from a refractive boundary at the display surface of the cover glass
Data Source
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AI summary
An electronic device includes a cover glass having a display surface, a pixelated photoemitting element array, and a pixelated photodetecting element array. The pixelated photoemitting element array emits a light signal through the cover glass to the display surface. The pixelated photodetecting element array is positioned relative to the pixelated photoemitting element array and the cover glass to receive a reflected light signal. The reflected light signal includes a portion of the emitted light signal reflected by total internal reflection from a refractive boundary at the display surface. Operation of each pixel is switched between the one or more photodetecting elements and the one or more photoemitting elements by the pixel selector signal component received from the pixel selector signal bus. A sensing trigger is configured to trigger the imaging scan by the pixelated photoemitting element array and the pixelated photodetecting element array, responsive to detection of an initiating action.