Dimming Layer for Optical Fingerprint Sensor Saturation
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Solution Overview
Problem
Under strong ambient light, existing optical fingerprint recognition systems using OLEDs and PIN photodiodes face saturation issues, leading to blurred fingerprint images due to light intensity differences, making it difficult to distinguish valley ridge signals effectively.
Innovation Solution
An image acquisition structure with a dimming layer covering a reference photosensor, a processing circuit to adjust input signals for image acquisition circuits, and a dynamic adjustment mechanism to prevent saturation, ensuring clear fingerprint recognition under varying light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If integration time is reduced to prevent PIN saturation under strong ambient light, then saturation is slowed, but the difference between light intensities reflected by valley ridges becomes very small, making it impossible to distinguish fingerprint signals
Solution Approach 1:
The patent introduces a dimming layer as an intermediary component between the ambient light source and the reference photosensor. This dimming layer attenuates the strong ambient light before it reaches the reference photosensor, preventing saturation while still allowing sufficient light to pass through for accurate fingerprint signal detection. The dimming layer acts as a mediator that balances the conflicting requirements of preventing saturation and maintaining signal distinction.
Solution Approach 2:
The patent applies preliminary action by pre-adjusting the light intensity before it reaches the photosensor through the dimming layer. The dimming layer is positioned to attenuate ambient light in advance, ensuring that the reference photosensor receives light within its optimal detection range before the actual fingerprint recognition process begins, thereby preventing saturation while maintaining signal quality.
2Measurement precision
If integration time is increased to improve signal detection, then fingerprint signal distinction improves, but the PIN reaches saturation under strong ambient light
Solution Approach 1:
The dimming layer serves as an intermediary that reduces ambient light intensity before it reaches the reference photosensor. This allows the system to maintain longer integration times for improved signal detection without causing PIN saturation, as the dimming layer ensures the light intensity remains within the photosensor's linear response range throughout the integration period.
3Reliability
If PIN dynamic range is increased from apparatus to handle strong ambient light, then saturation is prevented, but the system complexity and range increase significantly
Solution Approach 1:
Instead of increasing the PIN dynamic range through complex apparatus modifications, the patent uses a simple dimming layer as an intermediary to attenuate ambient light. This approach prevents saturation while maintaining the existing simple structure of the photosensor system, avoiding the need for complex dynamic range adjustment mechanisms.
Solution Approach 2:
The patent changes the light intensity parameter before it reaches the photosensor by introducing the dimming layer. This external parameter adjustment (light intensity reduction) achieves saturation prevention without requiring changes to the photosensor's intrinsic dynamic range parameters, thereby maintaining system simplicity.
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
The solution dynamically adjusts light intensity input to image acquisition circuits, preventing saturation and enhancing fingerprint recognition accuracy even under strong ambient light, ensuring clear and noise-free image acquisition.
Implementation Method 1
a first photosensor; the reference circuit is configured to receive light rays incident passing through the dimming layer, and output an electrical signal based on a light intensity of the light rays
Implementation Method 2
a dimming layer provided on a light incident side of the first photosensor; the reference circuit is configured to receive light rays incident passing through the dimming layer
Data Source
AI summary
An image acquisition structure includes a dimming layer, a processing circuit, a plurality of reference circuits and a plurality of image acquisition circuits. The reference circuit includes a first photosensor. The dimming layer is provided on a light incident side of the first photosensor, and covers at least the first photosensor of the reference circuit. An input terminal of the processing circuit is electrically connected to an output terminal of the reference circuit. Input terminals of the plurality of image acquisition circuits are electrically connected to an output terminal of the processing circuit.