Under-Display Optical Fingerprint Sensor Dark Current Compensation
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Solution Overview
Problem
Optical fingerprint sensor modules integrated under display panels face reduced accuracy due to dark currents generated by photodiodes not exposed to light, which occupy the dynamic range of sensing results.
Innovation Solution
The method involves displaying a black pattern by the display panel to measure dark currents, generating first and second sensing signals from sensor pixels, adjusting voltage levels of the second sensing signals based on the first signals, and creating an image of the object by eliminating components corresponding to dark current, thereby increasing the dynamic range of sensing results.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If photodiodes are integrated under the display panel for optical fingerprint sensing, then the full screen design is achieved and product appearance is improved, but dark currents are generated by photodiodes not exposed to light, reducing the accuracy of fingerprint imaging
Solution Approach 1:
The sensor pixels are divided into two functional groups: first sensor pixels arranged in a black pattern for dark current measurement, and second sensor pixels arranged in a contact area for fingerprint image sensing. This segmentation allows separate measurement and compensation of dark currents from actual fingerprint detection, resolving the accuracy issue while maintaining full screen design.
Solution Approach 2:
The system performs preliminary measurement of dark currents using first sensor pixels before capturing the actual fingerprint image. By measuring and compensating for dark currents in advance, the system eliminates their harmful effect on the dynamic range and accuracy of the fingerprint sensing result.
2Measurement precision
If dark current measurement and compensation is implemented, then the dynamic range of sensing results is improved, but the device complexity increases due to additional sensor pixels and signal processing
Solution Approach 1:
The display panel serves multiple functions: it acts as both the display interface and the light source for optical fingerprint sensing. The sensor pixels are integrated within the same display panel structure, allowing the panel to simultaneously perform display and sensing functions without requiring separate dedicated sensing hardware, thus limiting the increase in device complexity.
Solution Approach 2:
The first sensor pixels for dark current measurement and second sensor pixels for fingerprint sensing are merged into the same sensor array within the display panel. This unified structure allows shared readout circuits and processing infrastructure, reducing the overall complexity increase compared to having completely separate measurement and sensing systems.
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 enhances the accuracy of object identification by compensating for dark currents, allowing the full code range to be used for reflected light components, thus improving the dynamic range and accuracy of optical sensing results.
Implementation Method 1
The optical fingerprint sensor module generates a fingerprint image by measuring leakage currents of photodiodes that are exposed to light reflected by a fingertip
Data Source
AI summary
An object identifying method, suitable for an object identifying circuit configured to be disposed under a display panel, includes the following operations: displaying a black pattern by the display panel; generating a plurality of first sensing signals of a plurality of first sensor pixels of the display panel arranged in the black pattern; generating a plurality of second sensing signals of a plurality of second sensor pixels of the display panel arranged in a contact area with which the display panel contacting an object to be identified; adjusting voltage levels of the plurality of second sensing signals according to the plurality of first sensing signals; and generating an image corresponding to the object to be identified from the adjusted plurality of second sensing signals.