Capacitance Addition Transistor for Floating Diffusion Noise Reduction
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Solution Overview
Problem
Existing photoelectric conversion apparatuses face challenges in reducing floating diffusion (FD) capacitance while maintaining dynamic range, especially when multiple photoelectric conversion circuits share a floating diffusion node, leading to increased noise and reduced accuracy in low illuminance conditions.
Innovation Solution
The apparatus incorporates a capacitance addition transistor that connects the floating diffusion node to capacitor-connected transistors, allowing for separate control of signal charges from multiple photoelectric conversion circuits, reducing FD capacitance and extending dynamic range by using a capacitance addition transistor to manage capacitance effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple photoelectric conversion circuits share a floating diffusion node, then device complexity is reduced, but FD capacitance increases leading to increased noise and reduced measurement precision
Solution Approach 1:
The patent divides the floating diffusion node into multiple separate FD nodes, with each photoelectric conversion circuit having its own dedicated FD node. This segmentation prevents capacitance accumulation that would occur with shared FD nodes, thereby maintaining signal accuracy while accepting increased device complexity. The segmentation is achieved through separate transfer transistors and reset transistors for each circuit-FD pair.
Solution Approach 2:
The patent changes the capacitance parameter by reducing FD capacitance through separate FD nodes and by controlling the timing of capacitor connection to the FD node. The capacitance addition transistor enables dynamic adjustment of capacitance based on signal levels, allowing the system to optimize between noise reduction and dynamic range requirements.
2Measurement precision
If FD capacitance is reduced to improve signal accuracy, then measurement precision improves, but dynamic range is reduced
Solution Approach 1:
The patent introduces dynamic control of capacitance through the capacitance addition transistor, which can be turned on or off based on signal conditions. This allows the FD node capacitance to be adjusted dynamically: kept small for low-signal conditions to maintain precision, and increased when needed to extend dynamic range. The reset transistor also provides dynamic control by clearing accumulated charge.
Solution Approach 2:
The capacitor connected through the capacitance addition transistor acts as an intermediary element that can be selectively coupled to the FD node. This intermediary capacitance provides additional charge storage capacity when needed, extending dynamic range without permanently increasing the base FD capacitance that would otherwise limit precision in low-light conditions.
3Adaptability or versatility
If a capacitor is connected to the floating diffusion node to extend dynamic range, then adaptability improves, but FD capacitance increases leading to increased noise
Solution Approach 1:
The capacitance addition transistor provides dynamic control over capacitor connection to the FD node. The capacitor is connected only when needed (controlled by the capacitance addition transistor based on signal conditions), allowing the system to extend dynamic range temporarily without permanently increasing FD capacitance. This dynamic approach prevents noise increase during low-signal conditions while maintaining dynamic range extension capability when required.
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 reduces FD capacitance, enhances dynamic range, and improves signal accuracy by allowing separate management of signal charges from multiple photoelectric conversion circuits, even in low illuminance conditions, thereby reducing noise and increasing the apparatus's performance.
Implementation Method 1
a first photoelectric conversion circuit and a second photoelectric conversion circuit, a floating diffusion node
Data Source
AI summary
A photoelectric conversion apparatus includes first and second photoelectric conversion circuits, an FD configured to hold signal charges, a first transfer transistor configured to control transfer of the signal charge from the first photoelectric conversion circuit to the FD, a second transfer transistor configured to control transfer of the signal charge from the second photoelectric conversion circuit to the FD, a first capacitor circuit configured to hold a signal charge overflowing from the first photoelectric conversion circuit, and a second capacitor circuit configured to hold a signal charge overflowing from the second photoelectric conversion circuit. The first capacitor circuit is connected to a capacitance addition transistor via a first capacitor-connected transistor. The second capacitor circuit is connected to the capacitance addition transistor via a second capacitor-connected transistor. The first and second capacitor-connected transistors are connected to the FD via the capacitance addition transistor.