Image Sensor Pixel Readout for Focus Detection Accuracy
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Solution Overview
Problem
Existing image sensors with two photodiodes for each microlens face challenges in focus detection accuracy and readout time due to color component distribution and light source variations, particularly when a large amount of green color component is not present, and the need to read out signals from both photodiodes independently.
Innovation Solution
An image sensor with a matrix arrangement of unit pixels, each having two photodiodes, and color filters that allow different wavelengths, utilizing a control unit to drive control signal lines using a divided readout method for parallax signals and an added readout method for normal image signals, allowing for efficient phase difference detection and image capture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two photodiodes are provided for each microlens to enable phase difference detection, then focus detection capability is improved, but readout time increases significantly
Solution Approach 1:
The pixel array is divided into two distinct types: imaging pixels with two photodiodes for phase difference detection, and focus detection pixels with a single photodiode optimized for focus detection. This segmentation allows each pixel type to be optimized for its specific function, enabling parallel processing that reduces overall readout time while maintaining focus detection accuracy
Solution Approach 2:
The patent implements dynamic switching between different readout modes (imaging mode and focus detection mode) and allows flexible selection of which color filter pixels serve as focus detection pixels based on subject conditions. This dynamic adaptability optimizes readout efficiency while maintaining detection accuracy across varying shooting scenarios
2Measurement precision
If green filter pixels are used for focus detection based on spectral characteristics, then focus detection is optimized under certain conditions, but reliability decreases when subject color composition varies
Solution Approach 1:
Any color filter pixel (red, green, or blue) can serve as a focus detection pixel depending on the shooting conditions and subject characteristics. The system universally supports all color types for focus detection, switching between them based on which color channel provides the best focus detection performance for the current subject, thereby maintaining reliability across diverse color compositions
Solution Approach 2:
The system dynamically changes the operational parameter of which color filter pixels function as focus detection pixels based on analyzed image signals. When the subject lacks green color components or when other color channels provide better focus information, the system switches to using red or blue filter pixels respectively, adapting to varying color conditions to maintain reliable focus detection
3Device complexity
If all pixels are used for both imaging and focus detection, then device complexity is reduced, but measurement precision for focus detection decreases
Solution Approach 1:
Each pixel is clearly segmented into one of two types: imaging pixels with two photodiodes for capturing image information, or focus detection pixels with a single photodiode for optimized focus detection. This structural segmentation allows focus detection pixels to be dedicated solely to focus detection without the complexity of dual photodiode control, while maintaining high detection precision through dedicated optimization
Solution Approach 2:
Different regions of the pixel array have different functional qualities: imaging pixels are optimized for image capture with dual photodiodes, while focus detection pixels are optimized for focus detection with single photodiode design. This local differentiation of quality allows each region to perform its specific function with optimal precision without unnecessary structural 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
This approach increases focus detection accuracy and reduces signal readout time by optimizing the readout method based on the color composition of the subject, ensuring efficient phase difference detection and image signal generation.
Implementation Method 1
color filters, arranged for the plurality of unit pixels, respectively, that mainly pass light of wavelengths corresponding to different colors
Implementation Method 2
a plurality of photoelectric conversion portions for accumulating charge corresponding to a quantity of incident light
Data Source
AI summary
An image sensor comprising: a plurality of unit pixels, arranged in matrix, each having a plurality of photoelectric conversion portions for accumulating charge corresponding to a quantity of incident light; color filters, arranged for the plurality of unit pixels, respectively, that mainly pass light of wavelengths corresponding to different colors; first control signal lines arranged between every predetermined number of rows and connected to the unit pixels, included in the predetermined number of rows, corresponding to the color filters of a first color; and second control signal lines arranged between the every predetermined number of rows and connected to the unit pixels, included in the same predetermined number of rows that include the unit pixels corresponding to the color filters of the first color, corresponding to the color filters of a second color.