Solid-State Image Sensor Focus Detection Pixel Architecture
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Solution Overview
Problem
Existing solid-state image sensors face challenges in low illumination conditions, with decreased sensitivity and accuracy due to larger FD portions, increased power consumption, and higher costs associated with focus detection pixels, which affect image quality and yield.
Innovation Solution
A solid-state image sensor design where focus detection pixels share a floating diffusion layer and transfer gates with ordinary imaging pixels, allowing simultaneous control and operation, thereby improving focus detection accuracy and reducing power consumption and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If focus detection pixels have separate photoelectric conversion units and larger FD portions, then focus detection capability is improved, but sensitivity during low illumination decreases and detection accuracy deteriorates
Solution Approach 1:
The patent merges the photoelectric conversion units of multiple focus detection pixels to share a common floating diffusion layer. This consolidation increases the effective photoelectric conversion area while reducing the FD portion size, thereby improving low illumination sensitivity without sacrificing focus detection capability. The shared FD layer allows multiple pixels to contribute their charge signals, enhancing the signal-to-noise ratio in low light conditions.
Solution Approach 2:
The patent makes the floating diffusion layer serve multiple functions: it acts as both the charge storage node for focus detection pixels and the output node for ordinary imaging pixels. This multi-functionality eliminates the need for separate dedicated FD portions for focus detection pixels, improving area utilization and sensitivity while maintaining focus detection accuracy through the shared architecture.
2Measurement precision
If separate design for focus detection pixels is implemented, then focus detection function is improved, but number of steps increases and costs increase
Solution Approach 1:
The patent implements a universal design where focus detection pixels and ordinary imaging pixels share the same floating diffusion layer structure and readout circuitry. This eliminates the need for separate dedicated output nodes and reduces the number of manufacturing steps by using a common architecture for both pixel types, thereby lowering production costs while maintaining focus detection functionality.
Solution Approach 2:
The patent combines the output nodes of focus detection pixels with those of ordinary imaging pixels, merging previously separate signal paths into a unified readout system. This consolidation reduces circuit complexity, decreases the number of required manufacturing steps, and lowers overall system costs while preserving the ability to perform focus detection.
3Area of moving object
If focus detection pixels are miniaturized, then pixel density is improved, but color mixing occurs and high-level fine process is necessary
Solution Approach 1:
The patent merges the photoelectric conversion areas of multiple focus detection pixels into a larger shared region that feeds into a common floating diffusion layer. This approach allows individual pixels to be miniaturized while maintaining adequate separation between conversion areas, preventing color mixing. The shared FD layer acts as a consolidation point that eliminates the need for complex isolation structures between miniaturized 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 enhances focus detection accuracy during low illumination while maintaining image quality and reducing power consumption and production costs, enabling better miniaturization and sensitivity matching that of ordinary imaging pixels.
Implementation Method 1
a first photoelectric conversion unit, and a first transfer gate for reading out an electron generated through photoelectric conversion in the first photoelectric conversion unit
Data Source
AI summary
Provided is a solid-state image sensor including a pixel array portion formed from a two-dimensional array of ordinary imaging pixels each having a photoelectric conversion unit and configured to output an electric signal obtained through photoelectric conversion as a pixel signal, and focus detection pixels for detecting focus. The focus detection pixels include at least a first focus detection pixel and a second focus detection pixel each having a photoelectric conversion unit and configured to transfer and output an electric signal obtained through photoelectric conversion to an output node. The first focus detection pixel and the second focus detection pixel share the output node. The first focus detection pixel includes a first photoelectric conversion unit, and a first transfer gate for reading out an electron generated through photoelectric conversion in the first photoelectric conversion unit to the shared output node.