Under-Display Fingerprint Sensor Exposure Control for Flicker Noise
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Solution Overview
Problem
Fingerprint sensors using the rolling shutter method are prone to flicker noise due to varying exposure times of pixels caused by display on/off cycles, which can be exacerbated by oscillator clock variations, leading to inaccurate illuminance measurements and requiring additional circuitry to maintain an off ratio of 10% or higher.
Innovation Solution
The method adjusts the exposure time of fingerprint sensors based on analyzing flicker noise patterns in initial images, allowing for accurate fingerprint sensing without additional circuitry by dynamically adjusting pixel exposure times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the display off ratio is maintained at 10% or higher to minimize flicker noise in fingerprint images, then flicker noise is reduced, but the illuminance sensor cannot accurately measure external illuminance during the display off period
Solution Approach 1:
The system performs illuminance measurement during the display on period before the display turns off, so that the measurement is completed while the illuminance sensor can still detect light. This preliminary action ensures accurate illuminance data is obtained before the display off period begins, resolving the conflict between maintaining high off ratio for flicker reduction and enabling accurate illuminance measurement.
2Object-affected harmful factors
If a separate circuit is added to transmit display on/off period information to the fingerprint sensor, then flicker noise is minimized through precise exposure time control, but device complexity increases
Solution Approach 1:
The system merges the display controller and fingerprint sensor controller into a single integrated controller that can coordinate their operations. This unified controller internally manages the display on/off timing and synchronizes the fingerprint sensor exposure time without requiring separate communication circuits, thereby reducing device complexity while still achieving flicker noise minimization.
Solution Approach 2:
The controller is designed with multi-functionality to perform both display control and fingerprint sensor control. It can generate timing signals for both the display on/off transitions and the fingerprint sensor exposure timing, eliminating the need for separate dedicated circuits and reducing overall system complexity.
3Object-affected harmful factors
If the display refresh rate is increased to reduce flicker noise, then image quality improves, but power consumption increases
Solution Approach 1:
Instead of changing the display refresh rate parameter, the system changes the fingerprint sensor exposure time parameter to be synchronized with the existing display on/off periods. By adjusting the exposure timing to match the display timing, the system achieves flicker noise reduction without modifying the display refresh rate, thereby avoiding increased power consumption.
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 minimizes flicker noise and ensures high-quality fingerprint images by optimizing exposure times, improving accuracy and reducing the need for extra circuitry.
Implementation Method 1
obtain a second image using the fingerprint sensor by sensing the light reflected by the fingerprint of the user
Implementation Method 2
obtain a first image using the fingerprint sensor before the display emits light... obtain a second image using the fingerprint sensor by sensing the light reflected
Data Source
AI summary
An electronic device, including: a display; a fingerprint sensor under the display; one or more memories configured to store instructions; and one or more processors operable to execute the instructions to cause the electronic device to: detect an occurrence of an event for sensing a fingerprint of a user, based on detecting the occurrence, obtain a first image using the fingerprint sensor before the display emits light at a predetermined intensity for sensing the fingerprint, analyze at least one pattern corresponding to a flicker noise included in the first image to obtain an analysis result, based on the analysis result, adjust at least one exposure time of the fingerprint sensor for sensing the light reflected by the fingerprint of the user, and based on the adjusted at least one exposure time, obtain a second image using the fingerprint sensor by sensing the light reflected by the fingerprint of the user.