Hybrid Image Pixel Layout for PDAF Without Resolution Loss
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Solution Overview
Problem
Conventional image sensors face a trade-off between phase detection autofocus (PDAF) performance and image resolution, as dedicating subpixels to generate phase mismatch signals reduces image resolution, necessitating techniques to improve PDAF with minimal resolution penalty.
Innovation Solution
The use of differently sized micro-lenses overlying photodiodes and subpixels in a specific arrangement, where first micro-lenses are disposed over individual image subpixels and second micro-lenses over phase detection subpixels, allows for improved PDAF performance with negligible impairment to image resolution, akin to Bayer-pattern configured sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If subpixels are dedicated to generate phase mismatch signals for PDAF, then PDAF performance is improved, but image resolution deteriorates
Solution Approach 1:
The patent applies local quality by implementing different micro-lens sizes at different locations: larger micro-lenses (first micro-lenses) are positioned over phase detection subpixels to optimize phase mismatch signal generation, while smaller micro-lenses (second micro-lenses) are positioned over image subpixels to optimize image resolution. This spatial differentiation of optical component characteristics resolves the contradiction by allowing each region to be optimized for its specific function.
Solution Approach 2:
The patent segments the pixel array into distinct functional regions with different micro-lens characteristics. Phase detection subpixels are separated from image subpixels and assigned different optical focusing properties through differently sized micro-lenses. This segmentation allows independent optimization of PDAF performance in phase detection regions and image quality in imaging regions, eliminating the need to sacrifice one for the other.
2Measurement precision
If micro-lenses are configured for optimal PDAF, then phase detection accuracy is improved, but image quality deteriorates
Solution Approach 1:
Different micro-lens sizes are assigned to different functional regions: larger micro-lenses over phase detection subpixels enhance light gathering and phase signal accuracy, while smaller micro-lenses over image subpixels maintain higher spatial resolution for imaging. This local optimization resolves the contradiction between phase detection accuracy and image quality.
Solution Approach 2:
The patent creates a multi-functional pixel structure where each pixel contains both phase detection subpixels and image subpixels, with each subpixel type optimized for its specific function through dedicated micro-lens sizing. This universal design allows the same sensor to simultaneously perform both high-accuracy phase detection and high-quality imaging without compromising either function.
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 PDAF performance while maintaining or improving image resolution, offering a significant improvement over existing PDAF-enabled image sensors by generating phase mismatch signals with reduced loss in image data quality.
Implementation Method 1
first micro-lenses are disposed over individual photodiodes of the image subpixels, and a second micro-lens of a second size is disposed overlying the photodiodes included in the phase detection subpixel
Implementation Method 2
an image sensor implementing the Quad Photodiode (QPD) design includes four subpixels, each overlaid by a respective micro-lens
Data Source
AI summary
Image sensors for Phase-Detection Auto Focus (PDAF) are provided. An image sensor includes a pixel including a plurality of photodiodes disposed in a semiconductor material according to an arrangement. The arrangement defines a first image subpixel comprising a plurality of first photodiodes, a second image subpixel comprising a plurality of second photodiodes, and a third image subpixel including a plurality of third photodiodes, and a phase detection subpixel comprising a first photodiode, a second photodiode, or a third photodiodes. The pixel can include a plurality of first micro-lenses disposed individually overlying at least a subset of the plurality of photodiodes of the first, second and third image subpixels. The pixel can also include a second micro-lens disposed overlying the phase detection subpixel, a first micro-lens of the first micro-lenses having a first radius less than a second radius of the second micro-lens.