Photoelectric Conversion Device Dynamic Capacitance Switching
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Solution Overview
Problem
Conventional photoelectric conversion devices face challenges in extending dynamic range and maintaining image quality, particularly when capturing images with varying luminance levels, due to excessive potential drops in the floating diffusion (FD) node, which can lead to signal clipping and noise amplification.
Innovation Solution
The introduction of an additional capacitance transistor that switches capacitance at the FD node, allowing for increased charge holding capacity and voltage regulation, thereby extending dynamic range and improving sensitivity by controlling the capacitance and voltage levels through specific control signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional photoelectric conversion devices are used, then the structure is simple, but the dynamic range is limited due to excessive potential drops in the floating diffusion node
Solution Approach 1:
The patent applies the dynamics principle by introducing a switchable capacitance mechanism at the floating diffusion node. A first transistor is configured to switch between connecting and disconnecting a first capacitance from the floating diffusion node based on control signals. This dynamic switching capability allows the device to adapt its capacitance value according to lighting conditions, thereby extending the dynamic range without requiring completely different circuit architectures for different scenarios
Solution Approach 2:
The patent implements parameter changes by varying the capacitance value at the floating diffusion node through transistor switching. The first transistor changes the electrical parameter (capacitance) of the floating diffusion node between two states: with first capacitance connected and without first capacitance connected. This parameter variation enables the device to handle different luminance levels effectively, resolving the contradiction between maintaining simple structure and achieving extended dynamic range
2Adaptability or versatility
If the capacitance at the floating diffusion node is increased to extend dynamic range, then the dynamic range is improved, but the sensitivity decreases due to reduced voltage change for a given charge
Solution Approach 1:
The patent resolves this contradiction through dynamic capacitance switching. The first transistor switches the first capacitance based on control signals that correspond to different luminance conditions. Under low-light conditions, the first capacitance is disconnected to maintain high sensitivity (larger voltage change for given charge). Under high-light conditions, the first capacitance is connected to extend dynamic range by accommodating larger charge amounts without excessive potential drops. This temporal and conditional switching allows the system to optimize both sensitivity and dynamic range at different operating points
Solution Approach 2:
The patent employs periodic action through the timing of control signals that switch the first transistor. The control signals are applied in specific time sequences during the photoelectric conversion process - first during the accumulation period to control charge storage, then during the readout period to control signal transfer. This periodic switching enables the capacitance to be adjusted at appropriate moments in the operational cycle, resolving the trade-off between sensitivity and dynamic range
3Adaptability or versatility
If a switchable capacitance mechanism is added to extend dynamic range, then the adaptability is improved, but the device complexity increases
Solution Approach 1:
The patent applies universality by designing the first transistor to serve multiple functions within the pixel circuit. The first transistor not only switches the first capacitance to extend dynamic range but also participates in the overall charge transfer and signal readout process. By making this single component multi-functional, the patent achieves extended dynamic range capability without proportionally increasing the total number of components, thus mitigating the complexity increase
Solution Approach 2:
The patent implements merging by integrating the first capacitance and first transistor into the existing pixel circuit architecture rather than adding them as separate external components. The first capacitance is merged with the floating diffusion node, and the first transistor is merged into the signal processing path. This consolidation approach achieves the dynamic range extension功能 while minimizing the increase in device complexity by sharing circuit elements and space
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 solution enhances the dynamic range and sensitivity of the photoelectric conversion device, preventing excessive potential drops and maintaining high-quality image capture across a wide range of luminance levels by dynamically adjusting capacitance and voltage, thus improving image fidelity.
Implementation Method 1
The first transistor is connected to the input node and configured to switch a capacitance of the input node
Implementation Method 2
a photoelectric conversion element, an output transistor
Data Source
AI summary
A unit circuit includes a photoelectric conversion element, an output transistor including an input node and configured to output a signal based on a charge from the photoelectric conversion element, a reset transistor, and a first transistor connected to the input node and configured to change a capacitance of the input node. A first control signal supplied to a gate electrode of the first transistor has at least three types of voltages.