Image Sensor Pixel Circuit With Switchable Floating Diffusion Gain
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Solution Overview
Problem
Current image sensors, particularly CMOS image sensors, face challenges in optimizing conversion gain for varying operating modes, which affects signal-to-noise ratio and dynamic range in image capturing and recognition modes.
Innovation Solution
The image sensor employs a pixel structure with multiple floating diffusion regions connected through metal lines, allowing for adjustable conversion gain by controlling the size of the floating diffusion region based on operating modes, thereby optimizing capacitance and signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed conversion gain is used in CMOS image sensors, then the circuit design is simple, but the signal-to-noise ratio and dynamic range cannot be optimized for different operating modes
Solution Approach 1:
The patent implements dynamic conversion gain adjustment by enabling the connection between first and second floating diffusion regions through a switch controlled by a conversion gain control signal. This allows the pixel circuit to transition between different conversion gain states (first conversion gain when regions are connected, second conversion gain when disconnected), providing adaptability for different operating modes while maintaining a relatively simple circuit structure.
Solution Approach 2:
The patent changes the electrical parameters of the pixel circuit by varying the capacitance of the floating diffusion region. By controlling the connection state between the first and second floating diffusion regions, the total capacitance changes, which directly adjusts the conversion gain. This parameter change approach enables optimized signal-to-noise ratio and dynamic range for different operating modes without requiring completely different circuit designs.
2Reliability
If multiple floating diffusion regions are connected through metal lines to enable conversion gain control, then the signal-to-noise ratio and dynamic range are optimized, but the pixel structure becomes more complex
Solution Approach 1:
The patent merges multiple floating diffusion regions (first and second floating diffusion regions) into a single functional unit that can operate in different capacitance states. By connecting these regions through a metal line and switch, the circuit achieves multiple conversion gain levels while sharing common readout circuitry and control mechanisms, thus improving signal quality without proportionally increasing overall complexity.
Solution Approach 2:
The pixel circuit is designed with multi-functionality to handle different operating modes using the same physical structure. The first and second floating diffusion regions serve dual purposes: they can be connected to provide higher capacitance for one operating mode, or disconnected for lower capacitance in another mode. This universal design allows a single pixel structure to optimize performance across multiple scenarios.
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 enhances the signal-to-noise ratio and dynamic range by varying the conversion gain according to different operating modes, improving image quality and power efficiency.
Implementation Method 1
Each of the plurality of pixels may include at least two photodiodes
Data Source
AI summary
Provided is an image sensor including a first pixel including a first floating diffusion region and a second floating diffusion region, a second pixel including a first floating diffusion region, a second floating diffusion region, and a third floating diffusion region, a third pixel including a first floating diffusion region and a second floating diffusion region, and a fourth pixel including a first floating diffusion region, a second floating diffusion region, and a third floating diffusion region, wherein the second floating diffusion region of the first pixel and the second floating diffusion region of the second pixel are connected through a first metal line, and wherein the third floating diffusion region of the second pixel and the third floating diffusion region of the third pixel are connected through a second metal.