Image Sensor Pixel Merging for Dynamic Range
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Solution Overview
Problem
Current image sensing devices face challenges in achieving high dynamic range and efficiently adjusting conversion gain without increasing pixel size, particularly in low-illuminance and high-illuminance conditions.
Innovation Solution
The design incorporates a shared pixel structure with floating diffusion regions, where unit pixels are isolated by a device isolation structure and coupled through conductive lines to a common floating diffusion node, allowing for adjustment of conversion gain using a conversion gain transistor without increasing pixel size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a shared pixel structure with floating diffusion regions is used, then device complexity is reduced and manufacturing is simplified, but the ability to adjust conversion gain independently for each pixel is lost
Solution Approach 1:
Multiple floating diffusion regions from different unit pixels are merged and coupled to a common floating diffusion node through conductive lines. This merging reduces device complexity and enables shared readout circuitry while the conversion gain transistor provides centralized gain control for the combined signal path.
Solution Approach 2:
The conversion gain transistor dynamically changes the capacitance of the common floating diffusion node by adjusting its conductive state. This parameter change enables conversion gain adjustment without requiring separate control circuits for each pixel, resolving the contradiction between simplified structure and adaptability.
2Measurement precision
If pixel size is reduced to increase the number of pixels, then image resolution increases, but the dynamic range and photoelectric conversion capability of each pixel deteriorate
Solution Approach 1:
Adjacent unit pixels share a common floating diffusion node, effectively combining their photoelectric conversion capabilities. This merging allows smaller individual pixels to contribute to a collective signal with sufficient dynamic range while maintaining high pixel density for high resolution.
Solution Approach 2:
The conversion gain transistor provides dynamic adjustment of the common floating diffusion node capacitance, enabling the system to adapt its gain characteristics. This dynamic control compensates for the reduced individual pixel capability by adjusting the amplification of the combined signal from multiple small pixels.
3Adaptability or versatility
If conversion gain is adjusted using separate control circuits for each pixel, then adaptability is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The common floating diffusion node serves multiple functions: it collects photocharges from multiple unit pixels, provides centralized capacitance control through a single conversion gain transistor, and interfaces with the readout circuitry. This multi-functionality eliminates the need for separate control circuits while maintaining conversion gain adjustability.
Solution Approach 2:
A single conversion gain transistor controls the capacitance parameter of the common floating diffusion node, providing centralized gain control for multiple pixels. This approach achieves adaptability through a unified control mechanism rather than individual pixel control circuits, significantly reducing device 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 enables the image sensing device to acquire both low-illuminance and high-illuminance characteristics while maintaining a compact pixel structure, improving operational characteristics and dynamic range without enlarging the pixel size.
Implementation Method 1
a first photoelectric conversion element configured to generate photocharges in response to incident light
Data Source
AI summary
An image sensing device is disclosed. The image sensing device includes a first unit pixel provided with a first photoelectric conversion element and a first floating diffusion region, a second unit pixel provided with a second photoelectric conversion element and a second floating diffusion region, a third unit pixel provided with a third photoelectric conversion region and a third floating diffusion region, and a fourth unit pixel provided with a fourth photoelectric conversion element and a fourth floating diffusion region. The first to fourth unit pixels are isolated from each other by a first device isolation structure. The first to fourth floating diffusion regions are coupled to a common floating diffusion node through conductive lines. At least one unit pixel among the first to fourth unit pixels includes a conversion gain transistor coupled to the common floating diffusion node and configured to adjust capacitance of the common floating diffusion node in response to a gain control signal provided to the conversion gain transistor.