Imaging Device Floating Diffusion Dynamic Capacitance Control
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Solution Overview
Problem
Solid-state imaging devices face a trade-off between signal-to-noise ratio (S/N) and dynamic range due to the capacitance of the floating diffusion (FD), where low capacitance improves S/N but reduces dynamic range, and high capacitance widens dynamic range but degrades S/N, while existing solutions, such as dual-capacitance FDs, compromise on sensitivity and saturation charge.
Innovation Solution
The imaging device employs a pixel unit with a transfer section, converting section, output section, reset section, and connecting section, where the driving unit controls charge transfer and connection between FDs to optimize capacitance based on light intensity, using a connecting signal to connect or disconnect FDs of adjacent pixels, allowing for dynamic adjustment of capacitance to balance S/N and dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the floating diffusion (FD) has a low capacitance, then the signal-to-noise ratio (S/N) is improved, but the dynamic range is reduced
Solution Approach 1:
The patent applies dynamics by making the capacitance of the floating diffusion adjustable rather than fixed. The capacitance value changes dynamically based on the amount of charge accumulated in the photodiode. When charge amount is small, the FD maintains low capacitance for high gain and good S/N. When charge amount is large, the FD switches to high capacitance mode to accommodate more charge and expand dynamic range. This dynamic adjustment resolves the contradiction between S/N and dynamic range.
Solution Approach 2:
The patent changes the capacitance parameter of the floating diffusion based on operating conditions. By detecting the charge amount in the photodiode and accordingly adjusting the FD capacitance value, the system optimizes both S/N and dynamic range performance. Low capacitance is used for low-light conditions to maximize gain, while high capacitance is used for bright conditions to prevent saturation, thus resolving the parameter contradiction.
2Adaptability or versatility
If the floating diffusion (FD) has a high capacitance, then the dynamic range is widened, but the signal-to-noise ratio (S/N) is degraded
Solution Approach 1:
The system dynamically switches between high and low capacitance modes of the floating diffusion based on real-time charge detection. High capacitance mode is activated only when large amounts of charge are detected, ensuring dynamic range expansion is used only when necessary. This prevents continuous operation in high capacitance mode from degrading S/N, while still providing dynamic range expansion when needed.
Solution Approach 2:
The capacitance parameter of the FD is changed based on the charge amount detected in the photodiode. When the charge amount exceeds a threshold indicating bright conditions, the FD capacitance is increased to prevent saturation. This conditional parameter change ensures dynamic range is widened only when necessary, maintaining good S/N in low-light conditions where high capacitance would be detrimental.
3Adaptability or versatility
If dual-capacitance floating diffusion is used to achieve wide dynamic range, then the dynamic range is improved, but the area increases and sensitivity decreases
Solution Approach 1:
Instead of using a permanently large dual-capacitance structure, the patent implements a single FD that dynamically adjusts its capacitance value. This allows the system to achieve the functionality of dual-capacitance (low and high capacitance modes) without requiring the physical space of two separate capacitance structures. The dynamic switching capability provides wide dynamic range while maintaining a compact area.
Solution Approach 2:
The single floating diffusion structure is designed to perform multiple functions by changing its capacitance value. It can operate in low capacitance mode for high-sensitivity applications and switch to high capacitance mode for high-dynamic-range applications. This multi-functionality eliminates the need for separate dual-capacitance structures, reducing area while maintaining the ability to handle both low-light and bright conditions effectively.
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 imaging device to achieve an excellent S/N and wide dynamic range without increasing the area of the FD, thereby maintaining sensitivity and saturation charge, and avoids the limitations of dual-capacitance FDs, allowing for high-quality image capture across varying light conditions.
Implementation Method 1
the PD (photodiode) of each pixel in a solid-state imaging device such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) sensor generates a charge according to light received by the PD
Data Source
AI summary
Disclosed herein is an imaging device including: a pixel unit including a pixel disposed in a plane and a driving unit. The pixel includes an accumulating section configured to detect a physical quantity, and accumulate a charge corresponding to the physical quantity, a transfer section configured to transfer the charge from the accumulating section, a converting section configured to convert the charge into a voltage, an output section configured to output a signal of the voltage converted by the converting section, a reset section configured to reset the potential of the converting section, and a connecting section connected to the converting section. The driving unit is configured to transfer a signal for giving an instruction to transfer the charge, and a connecting signal for controlling connection and non-connection. The driving unit makes the charge transferred in a state of the converting sections being connected to each other.