Photoelectric Conversion Pixel Gain Switching for Wider Dynamic Range
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Solution Overview
Problem
There is a demand for a photoelectric conversion device that can effectively expand the dynamic range while outputting signals for focus detection, as existing devices do not adequately address this requirement.
Innovation Solution
The device includes a plurality of pixels with a first and second photoelectric conversion element, a micro-lens, a floating diffusion, and a transistor that switches on to add capacitance to the floating diffusion node, allowing for reading signals at different conversion gains by performing first and second reading operations in alternating periods, enhancing dynamic range expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single reading operation is performed at fixed gain, then the device structure is simple, but the dynamic range cannot be expanded
Solution Approach 1:
The patent applies dynamics by making the capacitance of the floating diffusion variable rather than fixed. A transistor (M5) is introduced to control the connection of an external capacitor (Cext) to the floating diffusion node, allowing the total capacitance to be dynamically adjusted between two states: Cfd (transistor off) and Cfd + Cext (transistor on). This dynamic capacitance adjustment enables the reading operation to be performed at two different conversion gains, thereby expanding the dynamic range while maintaining a relatively simple device structure.
Solution Approach 2:
The patent implements parameter changes by modifying the capacitance parameter of the floating diffusion node. By controlling the transistor switch to connect or disconnect the external capacitor, the capacitance value changes between two discrete levels. This parameter change directly affects the conversion gain of the photoelectric conversion element, enabling the system to adapt to different light intensity conditions and expand the measurable dynamic range.
2Measurement precision
If high gain is used for reading, then low-illuminance detection is improved, but signal saturation occurs in high-illuminance conditions
Solution Approach 1:
The patent uses dynamics to switch between two gain modes based on illuminance conditions. By controlling the transistor switch, the system can dynamically adjust the floating diffusion capacitance to achieve high gain (when transistor is off, capacitance = Cfd) for low-illuminance detection or low gain (when transistor is on, capacitance = Cfd + Cext) for high-illuminance conditions. This dynamic adaptation prevents signal saturation in bright conditions while maintaining high detection precision in dim conditions.
Solution Approach 2:
The patent applies parameter changes by adjusting the capacitance parameter to control conversion gain. When the transistor is in the off-state, the capacitance is Cfd providing high conversion gain for sensitive low-illuminance detection. When the transistor is in the on-state, the capacitance increases to Cfd + Cext, reducing the conversion gain to prevent signal saturation in high-illuminance conditions. This parameter switching enables the system to optimize measurement precision across different light levels.
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 enables improved dynamic range expansion and reduced noise, particularly in low-illuminance conditions, by allowing the device to switch between high and low gain states based on illuminance levels, effectively capturing a broader range of light amounts without signal saturation.
Implementation Method 1
a first photoelectric conversion element, a second photoelectric conversion element, a micro-lens that guides incident light to the first photoelectric conversion element and the second photoelectric conversion element
Data Source
AI summary
A photoelectric conversion device includes a first photoelectric conversion element, a second photoelectric conversion element, a microlens that guides incident light to the first photoelectric conversion element and the second photoelectric conversion element, a floating diffusion to which charges accumulated in at least one of the first photoelectric conversion element and the second photoelectric conversion element are transferred, and a transistor that, when switched on, adds a capacitance to a node of the floating diffusion. First and second reading operations are performed. In the first reading operation, a signal based on charges transferred to the floating diffusion is read at a first conversion gain caused by a state where the transistor is in an off-state. In the second reading operation, a signal based on charges transferred to the floating diffusion is read at a second conversion gain caused by a state where the transistor is in an on-state.