Image Sensor Focus Detection Pixel Signal Level Reduction
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Solution Overview
Problem
Image-capturing devices face challenges in focus detection due to saturation issues with focus detection pixels, leading to inadequate exposure periods that result in either saturated focus detection or dark image-capturing pixel outputs, preventing effective focus adjustment.
Innovation Solution
An image sensor design with image-capturing pixels and focus detection pixels, where the signal level of focus detection signals is adjusted to be equal to or less than that of image signals through the use of reduction units, such as light reducing filters and different photoelectric conversion characteristics, ensuring optimal exposure and preventing saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the exposure period is shortened to prevent saturation of focus detection pixels, then focus detection can be executed, but the image-capturing pixel output levels become insufficient resulting in dark images
Solution Approach 1:
The patent divides the pixel array into distinct image-capturing pixels and focus detection pixels, allowing independent optimization of exposure parameters for each function. Image-capturing pixels use one exposure period optimized for image quality, while focus detection pixels use a separate, shorter exposure period optimized for focus detection, eliminating the need to compromise image brightness for focus detection capability.
Solution Approach 2:
The patent implements dynamic control of exposure periods, where the exposure time for focus detection pixels is independently adjustable and optimized based on lighting conditions and focus detection requirements, while image-capturing pixels maintain their optimal exposure time for image quality. This dynamic parameter control allows both functions to operate at peak performance simultaneously.
2Illumination intensity
If the exposure period is extended to ensure sufficient image-capturing pixel output levels, then image quality is maintained, but the outputs from focus detection pixels become saturated preventing focus detection
Solution Approach 1:
The patent separates the pixel array into dedicated image-capturing pixels and focus detection pixels, enabling independent exposure control. Image-capturing pixels can use extended exposure periods for optimal image brightness without causing saturation in focus detection pixels, which use shorter exposure periods optimized for their specific function.
Solution Approach 2:
The patent implements independent dynamic control of exposure periods for different pixel types. Image-capturing pixels maintain optimal exposure time for image quality, while focus detection pixels use separately optimized exposure time, allowing both to operate at peak performance without mutual interference or saturation issues.
3Device complexity
If focus detection pixels and image-capturing pixels assume the same pixel size and structure, then device complexity is reduced, but focus detection pixels become prone to saturation under conditions where image-capturing pixels remain unsaturated
Solution Approach 1:
The patent applies different characteristics to different regions of the pixel array. Focus detection pixels are equipped with specific optical elements (such as microlenses with different focal lengths or different spectral sensitivity) and independent exposure control, allowing them to optimize focus detection performance without being constrained by the uniform structure needed for image-capturing pixels.
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 design allows for effective focus detection while maintaining image quality by ensuring focus detection signals do not exceed image signals, preventing saturation and enabling accurate focus adjustment without compromising image brightness.
Implementation Method 1
a focus detection photoelectric conversion unit that converts the focus detection light flux received thereat to a focus detection signal
Implementation Method 2
an image-capturing photoelectric conversion unit that converts the partial light flux received thereat to an image signal
Data Source
AI summary
An image sensor includes: a plurality of image-capturing pixels that, upon each receiving a partial light flux within a predetermined wavelength range, which is part of a photographic light flux used to form an optical image, output image signals corresponding to the optical image; a plurality of focus detection pixels that receive a pair of focus detection light fluxes in a wider wavelength range than the predetermined wavelength range and output a pair of focus detection signals; and a reduction unit that adjusts a signal level of the focus detection signals output from the plurality of focus detection pixels to be equal to or less than a signal level of the image signals each output from one of the plurality of image-capturing pixels under a given light receiving condition.