Light-Sensing Display Pixels for Accurate In-Panel Bio-Sensing
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Solution Overview
Problem
Existing display devices face sensing errors due to images displayed before bio-sensing operations, which affect the accuracy of bio-sensing operations like fingerprint sensing and photoplethysmography, as the size of the display region is reduced and the bezel is increased when separate sensors are used.
Innovation Solution
Incorporating a display device with a light sensing pixel having an organic photodiode, the panel driver controls the light emitting pixel to emit light at different luminances in specific periods, resetting the organic photodiode, and receiving sensing currents to minimize the impact of previous images on sensing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate sensor is used for bio-sensing operations, then sensing functionality is achieved, but the display region size is reduced and bezel size is increased
Solution Approach 1:
The patent combines the light sensing pixel with the display pixel structure, integrating the organic photodiode into the display panel. This merging allows the display device to perform both display and bio-sensing functions using the same physical space, eliminating the need for separate sensors and maximizing the display region area.
2Productivity
If an image is displayed before a sensing operation, then the display function is performed, but sensing accuracy is degraded due to sensing errors
Solution Approach 1:
The patent applies a reset signal to the organic photodiode before the sensing operation to clear any residual charge from previously displayed images. This preliminary reset action ensures that the photodiode starts from a known initial state, eliminating afterimage effects and ensuring accurate sensing measurements.
Solution Approach 2:
The patent implements a periodic sensing operation mode where the display alternates between normal display operation and sensing operation. During sensing periods, the light emitting pixel emits light at a specific luminance level while the photodiode integrates the reflected light signal. This periodic alternation allows the system to perform both display and sensing functions accurately without interference from continuous image display.
3Illumination intensity
If the light emitting pixel emits light at high luminance continuously, then visibility is improved, but the organic photodiode accumulates charge causing sensing errors
Solution Approach 1:
The patent uses periodic action by alternating between display mode and sensing mode. During sensing mode, the light emitting pixel emits light at a controlled luminance level for a specific duration to allow the photodiode to integrate the reflected light signal from the user's finger. This periodic emission prevents continuous charge accumulation while still providing sufficient light for accurate sensing.
Solution Approach 2:
The patent changes the luminance parameter of the light emitting pixel based on the operation mode. During sensing operations, the luminance is adjusted to an optimal level that provides sufficient light for the photodiode to detect reflected light from the finger, while avoiding excessive luminance that would cause charge saturation. This dynamic parameter adjustment ensures both visibility and sensing accuracy.
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 effectively reduces sensing errors by normalizing the internal node voltages of light sensing pixels, ensuring accurate bio-sensing operations by adjusting luminance levels and resetting the organic photodiode, thereby enhancing the reliability of fingerprint sensing and photoplethysmography.
Implementation Method 1
a light sensing pixel having an organic photodiode within a sensing region
Data Source
AI summary
A display device includes: a display panel including a light emitting pixel having a light emitting element and a light sensing pixel having an organic photodiode within a sensing region; and a panel driver configured to drive the display panel, the panel driver further configured to: drive the light emitting pixel to emit light with a first luminance in a first period; reset the organic photodiode of the light sensing pixel in a second period; drive the light emitting pixel to emit light with a second luminance such that the organic photodiode receives reflected light in a third period; and receive a sensing current corresponding to an intensity of the reflected light from the light sensing pixel in a fourth period, wherein the first luminance in the first period is higher than the second luminance in the third period.