Under-Display Fingerprint Sensor Timing for Band Noise Reduction
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Solution Overview
Problem
Under-display fingerprint sensors in electronic devices suffer from noise and image quality issues due to inconsistent light exposure across sensor lines, caused by staggered integration times and varying display frame times, leading to horizontal bands and reduced recognition accuracy.
Innovation Solution
Synchronize the integration time of the fingerprint sensor with the display panel timing signal using trigger signals from the display driver integrated circuit to ensure consistent light exposure across all sensor lines, reducing noise and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the display panel uses multi-cycle pulse width modulation for brightness control, then display brightness precision is improved, but fingerprint image quality deteriorates due to noise and horizontal bands
Solution Approach 1:
The patent applies periodic action by synchronizing the fingerprint sensor's integration time window with the display's emission cycles. The sensor integrates light only during periods when the display is actively emitting light, excluding periods when the display is dimmed or off. This periodic synchronization ensures that each sensor line captures light during the same phase of the emission cycle, eliminating the horizontal banding noise while preserving the benefits of multi-cycle pulse width modulation for brightness control.
2Manufacturing precision
If the fingerprint sensor integration time is set to a fixed multiple of display frame time, then horizontal band noise is reduced, but synchronization accuracy deteriorates due to variations in frame time and integration time
Solution Approach 1:
The patent implements feedback by having the fingerprint sensor controller continuously monitor the actual display frame timing and emission cycle timing, then dynamically adjust the sensor integration time window to maintain precise synchronization. Instead of using a fixed multiple relationship, the system receives timing information from the display driver and adjusts its integration periods accordingly, compensating for variations caused by temperature, pressure, and manufacturing tolerances. This closed-loop approach maintains synchronization accuracy under varying operating conditions.
3Manufacturing precision
If the display mode is changed to single-cycle emission mode during fingerprint capture, then fingerprint image quality is improved, but display stability deteriorates due to mode transition flicker
Solution Approach 1:
The patent applies segmentation by dividing the fingerprint capture process into discrete time segments that align with the display's existing emission cycles. Instead of switching to a different display mode, the sensor is configured to integrate light only during specific segments of the multi-cycle emission pattern. This allows the display to maintain its normal multi-cycle operation for both visual output and fingerprint sensing, eliminating the need for mode transitions and associated flicker while still achieving consistent light exposure across sensor lines.
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 synchronization method enhances fingerprint image quality by equalizing light capture across sensor lines, reducing noise and improving recognition accuracy.
Implementation Method 1
The under-display fingerprint sensor captures photons of light that are produced by pixels of the display panel and reflected off of a finger placed on the display panel
Data Source
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AI summary
Methods, systems, and apparatus, including computer programs encoded on computer storage media, for under-display fingerprint sensor timing control are disclosed. A method includes receiving, by fingerprint sensor control circuitry, an indication to activate a fingerprint sensor that is located under a display panel of a computing device, the fingerprint sensor attached with respect to the display panel such that the fingerprint sensor is exposed to light produced by the display panel and reflected off a finger placed over the display panel at a location of the fingerprint sensor; outputting, for receipt by the fingerprint sensor, a start¬ sensing trigger signal at a start time synchronized with a display panel timing signal that is provided to the display panel to control emission of the display panel; and outputting, for receipt by the fingerprint sensor, a stop-sensing trigger signal at a stop time synchronized with the display panel timing signal.