Shared Floating Diffusion Pixels for Multi-Resolution Autofocus
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Solution Overview
Problem
Image sensors face challenges in accurately performing auto-focus functions across varying illumination environments, particularly in transitioning between high and low resolution modes without compromising image quality.
Innovation Solution
The image sensor employs a pixel array with adjacently disposed subpixels sharing a floating diffusion region, controlled by a row driver to adapt the auto-focus function across multiple resolution modes, allowing for precise focus detection in high, medium, and low resolution settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the image sensor uses separate pixel structures for different resolution modes, then the auto-focus function can be optimized for each mode, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent implements a universal pixel structure where adjacent subpixels share a common floating diffusion region and readout circuitry. This single structure serves multiple functions: it enables high-resolution mode by individually addressing subpixels, supports medium-resolution mode by combining adjacent subpixel groups, and provides low-resolution mode by further aggregating pixels. The shared floating diffusion region allows the same hardware to perform auto-focus detection across all resolution modes without requiring separate dedicated structures for each mode, thereby maintaining auto-focus accuracy while reducing device complexity.
Solution Approach 2:
The patent merges adjacent subpixels to share common readout circuitry and floating diffusion regions. By combining multiple subpixels into a shared structure, the patent reduces the overall number of independent circuit elements required in the image sensor. This merging approach allows the sensor to achieve multiple resolution modes (high, medium, and low) using the same physical infrastructure, eliminating the need for separate pixel structures for each resolution mode and thereby reducing device complexity while maintaining auto-focus functionality across all modes.
2Adaptability or versatility
If the image sensor integrates multiple resolution modes in a single chip, then productivity and versatility improve, but the manufacturing precision requirements increase
Solution Approach 1:
The patent segments the image sensor into multiple resolution modes by selectively activating and combining different groups of subpixels. The sensor array is divided into pixel groups where adjacent subpixels can be individually addressed for high-resolution mode or combined into larger effective pixels for medium and low-resolution modes. This segmentation approach allows the same physical sensor to provide multiple resolution capabilities without requiring separate chips or complex multi-layer structures, thereby improving versatility while keeping manufacturing precision requirements manageable through standard single-chip fabrication processes.
3Device complexity
If the image sensor uses a shared floating diffusion region for adjacent subpixels, then the device complexity is reduced, but the measurement precision for auto-focus may be compromised
Solution Approach 1:
The patent implements dynamic control of the shared floating diffusion region through timing-based signal isolation. During auto-focus detection, the readout circuitry sequentially activates different subpixels sharing the same floating diffusion region and uses timing control to prevent signal crosstalk. The circuit dynamically switches between different subpixel combinations based on the selected resolution mode and auto-focus requirements, ensuring that even though the physical structure is shared, the measurement precision required for accurate focus detection is maintained through temporal separation of signals.
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 configuration enables accurate and efficient auto-focus performance across different illumination environments by selectively using pixel units or pixel groups, ensuring optimal image quality in various resolution modes.
Implementation Method 1
Each pixel in the plurality of pixels comprises a micro-lens, a first subpixel including a first photodiode, a second subpixel including a second photodiode
Data Source
AI summary
An image sensor operating in multiple resolution modes including a low resolution mode and a high resolution mode includes a pixel array including a plurality of pixels, wherein each pixel in the plurality of pixels comprises a micro-lens, a first subpixel including a first photodiode, a second subpixel including a second photodiode, and the first subpixel and the second subpixel are adjacently disposed and share a floating diffusion region. The image sensor also includes a row driver providing control signals to the pixel array to control performing of an auto focus (AF) function, such that performing the AF function includes performing the AF function according to pixel units in the high resolution mode and performing the AF function according to pixel group units in the low resolution mode. A resolution corresponding to the low resolution mode is equal to or less than ¼ times a resolution corresponding to the high resolution mode.