Image Sensor Shared Pixel Readout for Auto-Focus and Preview
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Solution Overview
Problem
Conventional auto-focus techniques in digital imaging devices are limited in capturing sharp images, especially in images with varying intensity/color values, and can be improved for both auto-focus and preview capabilities.
Innovation Solution
An image sensor with a shared pixel readout design that simultaneously reads and adds image information from groups of light sensor cells, improving sensitivity and signal-to-noise ratio by increasing the fill factor and using separate AGC/AEC circuitries for auto-focus and preview, and implementing a 4T cell architecture for enhanced charge binning and True Correlated Double Sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional auto-focus techniques use digital filtering on digitized image data to determine focus, then the focus condition can be determined, but the technique is less effective in images with widely varying intensity/color values since averaging distorts results
Solution Approach 1:
The patent extracts only the necessary pixels (e.g., corner pixels or specific pattern pixels) from the image sensor for auto-focus determination, rather than using all pixels. This extraction allows focus measurement without the distorting effect of averaging across pixels with widely varying intensity values, thereby maintaining measurement precision while improving reliability in challenging imaging conditions
Solution Approach 2:
The patent segments the image sensor output into different pixel groups, separating the autofocus-dedicated pixels from the main imaging pixels. This segmentation allows independent optimization of the autofocus measurement path, enabling accurate focus determination through methods like variance calculation on selected pixels without being affected by the averaging distortion that occurs when processing the entire image
2Ease of operation
If image sensors provide preview capabilities by scaling down images for small screens, then users can view images prior to taking a picture, but the sensitivity and signal-to-noise ratio are reduced
Solution Approach 1:
The patent segments the pixel array into dedicated preview pixels and autofocus pixels, allowing the preview function to operate on a subset of pixels with proper signal processing. This segmentation enables preview generation without requiring full-image processing, maintaining signal-to-noise ratio while providing ease of operation through real-time preview capability
Solution Approach 2:
The patent changes the operational parameters by using separate analog gain control (AGC) and automatic exposure control (AEC) circuitries for different pixel groups. This parameter separation allows the preview function to be optimized independently, maintaining high signal-to-noise ratio through proper gain and exposure control even when operating at reduced resolution for preview display
3Measurement precision
If separate AGC/AEC circuitries are used for auto-focus and preview, then sensitivity and signal-to-noise ratio are improved, but device complexity increases
Solution Approach 1:
The patent implements multi-functional circuitry where the separate AGC/AEC circuitries serve dual purposes: they process signals for both preview and autofocus functions simultaneously. This universality allows the additional circuitry to benefit multiple functions rather than creating redundant systems, thereby improving signal-to-noise ratio while minimizing the increase in overall device complexity
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 enhances the sensitivity and signal-to-noise ratio of the image sensor, allowing for better auto-focus and preview capabilities, improved light capture, and reduced noise, enabling finer lens adjustments and higher frame rates.
Implementation Method 1
Each light sensor cell includes a photosensitive element and a floating diffusion region
Data Source
AI summary
Embodiments of the present invention are directed to a plurality of light sensor cells disposed in a substrate in a shared pixel arrangement. Common readout circuitry is used to simultaneously read out image information from a group of light sensor cells. The image information from the group of light sensor cells is added together simultaneously and coupled to auto-focus circuitry and/or preview circuitry to provide for better lens adjustments and preview display.