Wide Dynamic Range Pixel Circuit With Multi-Photodiode Gain Switching
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Solution Overview
Problem
Existing image sensors face challenges in achieving high dynamic range while reducing pixel size, as technologies like split photodiode pixels struggle to maintain high conversion gain and increase the total number of pixels.
Innovation Solution
The image sensor design incorporates multiple photoelectric conversion element groups with different numbers of photodiodes, where the first group operates at low illuminance and the second group at high illuminance, with a unique floating diffusion region structure allowing for high and low conversion gain modes, enabling improved dynamic range and reduced pixel size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If split photodiode pixel technology is used to achieve high dynamic range, then dynamic range is improved, but pixel size cannot be reduced effectively
Solution Approach 1:
The pixel is divided into multiple photoelectric conversion elements (first photoelectric conversion element, second photoelectric conversion element, third photoelectric conversion element) with different light receiving areas. Each element is connected to separate floating diffusion regions (first, second, third floating diffusion regions) that can be selectively coupled through switching transistors. This segmentation allows independent operation of each element, enabling flexible combination of different conversion gains to achieve high dynamic range while maintaining compact pixel layout.
Solution Approach 2:
The patent implements dynamic switching between different photoelectric conversion elements and their corresponding floating diffusion regions through control signals. The switching transistors (first switching transistor, second switching transistor, third switching transistor) enable real-time reconfiguration of the pixel circuit, allowing the system to adaptively select high conversion gain mode (using smaller elements) or low conversion gain mode (using larger elements) based on illumination conditions, thereby achieving high dynamic range without increasing pixel size.
2Adaptability or versatility
If multiple photodiodes with different light receiving areas are configured, then conversion gain flexibility is improved, but device complexity increases
Solution Approach 1:
The patent designs a universal pixel structure where multiple photoelectric conversion elements share common circuit components including the driving transistor, reset transistor, and output transistor. The first, second, and third floating diffusion regions can be selectively connected to the output node through switching transistors, allowing the same pixel circuit to perform multiple functions (high conversion gain mode, low conversion gain mode, and intermediate modes) without requiring completely separate circuit paths for each mode.
Solution Approach 2:
The patent merges multiple photoelectric conversion elements and their associated floating diffusion regions into a single integrated pixel unit. The switching transistors are strategically positioned to enable selective coupling between the different floating diffusion regions and the output node, combining the functionality of multiple elements while sharing common readout circuitry. This merging approach reduces the overall complexity compared to having completely separate circuits for each conversion gain mode.
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 the dynamic range of the image sensor while allowing for a smaller pixel size, improving sensitivity and image quality across varying illumination environments.
Implementation Method 1
An image sensor is a device that converts a light signal into an electrical signal
Data Source
AI summary
Disclosed is an image sensor. The image sensor includes a plurality of pixels, one of which includes: a driving transistor; a first switching transistor; a first photoelectric conversion element group with first photoelectric conversion elements; a second photoelectric conversion element group with at least one second photoelectric conversion element; a first floating diffusion region connected to the first photoelectric conversion elements through a first transfer transistor; a second floating diffusion region connected to the at least one second photoelectric conversion element through a second transfer transistor; a third floating diffusion region connected to a gate of the driving transistor, and separated from each of the first floating diffusion region and the second floating diffusion region by the first switching transistor; and a reset transistor with a first end to which a reset voltage is applied and a second end connected to the third floating diffusion region.