Split-Photodiode Image Sensor Reset Layout for Dynamic Range
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Solution Overview
Problem
Image sensors with split-photodiode structures face challenges in processing reset and pixel signals from multiple photodiodes without deteriorating image quality, particularly due to differences in reset power supply voltages leading to clock feedthrough phenomena that affect the operating ranges of driving transistors.
Innovation Solution
The image sensor design includes a plurality of pixels with specific transistor configurations, such as first and second reset transistors, transfer transistors, and driving transistors, connected to floating diffusion nodes and column lines, allowing for independent reset and operation of photodiodes with different light-receiving areas, and using a second reset transistor to reduce voltage differences and prevent image quality deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a plurality of photodiodes with different light-receiving areas are included in one pixel to increase dynamic range, then the dynamic range is improved, but image quality deteriorates due to reset level and pixel level differences
Solution Approach 1:
The pixel is segmented into multiple photodiodes (first photodiode with larger area, second photodiode with smaller area) that can be independently exposed and reset. Each photodiode has dedicated transfer transistors and floating diffusion nodes, allowing separate signal processing paths that prevent cross-interference and maintain image quality while extending dynamic range
Solution Approach 2:
Floating diffusion nodes (first floating diffusion node, second floating diffusion node) are introduced as intermediary elements between the photodiodes and the output circuit. These intermediaries enable independent reset and signal transfer from each photodiode, allowing the system to manage multiple signal levels without direct interference, thus maintaining image quality while achieving high dynamic range
2Manufacturing precision
If dedicated reset transistors are added for each photodiode to manage reset levels independently, then image quality is maintained, but device complexity increases
Solution Approach 1:
The reset transistors (first reset transistor, second reset transistor) are designed with multi-functionality to handle both reset operations and signal transfer functions. By carefully designing the transistor configuration where reset transistors can serve dual purposes, the patent reduces the need for additional dedicated components, thereby managing device complexity while maintaining image quality
Solution Approach 2:
The patent merges the reset function and signal transfer function into a unified transistor configuration. The reset transistors are integrated with the transfer transistor structure, allowing a single transistor to perform both resetting the floating diffusion node and transferring the signal, thus reducing overall device complexity while maintaining precise control over reset levels
3Manufacturing precision
If independent transfer transistors are used for each photodiode to prevent signal interference, then image quality is preserved, but the number of transistors per pixel increases
Solution Approach 1:
The transfer transistors are designed to perform multiple functions: signal transfer from photodiodes, reset operations, and signal level management. By making these transistors multi-functional, the patent reduces the total number of transistors needed while maintaining independent signal paths that prevent interference and preserve image quality
Solution Approach 2:
The patent combines multiple transistor functions into a single integrated configuration. The transfer transistors are merged with reset transistor functionality, allowing one transistor to handle both signal transfer and reset operations for each photodiode, thereby reducing device complexity while maintaining signal separation
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 effectively prevents image quality deterioration by ensuring that reset and pixel levels remain within the operating range of the driving transistors, even under varying illumination conditions, thereby maintaining image quality across different exposure modes.
Implementation Method 1
Image sensors generate images of objects by using photoelectric conversion elements that react according to the intensity of light reflected from the objects
Data Source
AI summary
An image sensor includes a plurality of pixels, each pixel of the plurality of pixels includes, a first photodiode, a second photodiode, a first transfer transistor connected to a first floating diffusion node, a second transfer transistor connected to a second floating diffusion node, a first reset transistor configured to reset the first floating diffusion node with a first reset power supply voltage, a second reset transistor configured to reset the second floating diffusion node with a second reset power supply voltage, a switch transistor connecting the second floating diffusion node to the first floating diffusion node, and a first driving transistor configured to output an output voltage according to a voltage of the first floating diffusion node.