Fingerprint Sensor Pixel Gain Layout to Prevent Overexposure Blur
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Solution Overview
Problem
Fingerprint recognition accuracy is compromised due to overexposure, which blurs fingerprint features when increasing light illuminance or exposure time is used to enhance image quality in optical fingerprint sensors.
Innovation Solution
A fingerprint sensing device with pixel blocks arranged in an array, where each pixel block has a distinct conversion gain, with the central pixel block having the minimum conversion gain, and surrounding blocks having progressively higher conversion gains, enhancing image quality without blurring central features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If illuminance of light or exposure time is increased to enhance fingerprint image quality, then image quality is improved, but fingerprint feature may be blurred due to overexposure
Solution Approach 1:
The patent divides the pixel array into multiple regions with different conversion gains. Central pixel blocks use a first conversion gain to maintain appropriate exposure and prevent overexposure blurring, while peripheral pixel blocks use a second conversion gain (higher than the first) to compensate for lower light intensity at edges. This local differentiation of conversion gains allows each region to be optimized for its specific lighting conditions, improving overall image quality without causing overexposure artifacts that would degrade fingerprint recognition accuracy.
2Power
If conversion gain is increased to enhance signal intensity, then signal intensity is improved, but central region may become overexposed
Solution Approach 1:
The patent implements spatially varying conversion gains across the pixel array. Central pixel blocks are assigned a lower first conversion gain to prevent overexposure in regions receiving higher light intensity, while peripheral pixel blocks are assigned a higher second conversion gain to boost signal intensity in regions with lower light intensity. This localized adjustment of conversion gain ensures that signal intensity is enhanced where needed without causing overexposure in well-lit central regions.
Solution Approach 2:
The patent changes the conversion gain parameter across different spatial regions of the pixel array. By varying the conversion gain from a first value in central regions to a second value in peripheral regions, the system adapts the signal amplification characteristic to match the spatial distribution of light intensity, thereby enhancing signal intensity in dark regions while maintaining appropriate exposure levels in bright central regions.
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 gradient conversion gain design enhances signal intensity at dark corners of the fingerprint image, maintaining central image brightness and preventing feature blurring, thus improving fingerprint image quality and recognition accuracy.
Implementation Method 1
Each of the pixel blocks includes a conversion gain... The transfer transistor includes a first end, a second end and a control end. The first end of the transfer transistor is coupled to the second end of the photodiode... The transfer transistor converts electrons generated from the photodiode into a sensing voltage at the floating node according to the conversion gain
Data Source
AI summary
A fingerprint sensing device including a plurality of pixel blocks is provided. The pixel blocks are arranged in an array. Each of the pixel blocks includes a conversion gain. At least two of the conversion gains are different, and the pixel block located in a central location of the array has a minimum conversion gain.