CMOS Image Sensor Pixel Dynamic Voltage Supply
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Solution Overview
Problem
CMOS image sensors face challenges with global shutter efficiency due to charge leakage and generation at the floating diffusion node, leading to image artifacts and degraded picture quality, especially when capturing high-speed subjects.
Innovation Solution
A semiconductor circuit design that includes a reset gate transistor with a dynamic voltage supply, where the drain voltage is alternately set to minimize off-state leakage during signal hold time, reducing voltage changes at the floating diffusion node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a global shutter method is employed to capture high-speed subjects, then image artifacts are eliminated, but charge leakage at the floating diffusion node increases causing degraded picture quality
Solution Approach 1:
The patent applies dynamics by switching the floating diffusion node between two different voltage states: a first voltage (e.g., 0V) during signal hold time to minimize leakage, and a second voltage (e.g., reset voltage) during readout operations. This dynamic voltage adjustment resolves the contradiction by adapting the node's electrical state to the operational phase, reducing charge leakage while maintaining global shutter functionality.
Solution Approach 2:
The patent changes the voltage parameter of the floating diffusion node based on operational requirements. By transitioning the node voltage between a first level (minimizing leakage) and a second level (enabling readout), the system optimizes charge retention during the extended hold time required for global shutter operation, thereby improving picture quality without sacrificing the global shutter benefit.
2Adaptability or versatility
If the floating diffusion node holds the image signal for extended periods, then global shutter capability is achieved, but charge generation and leakage degrade the signal
Solution Approach 1:
The patent implements dynamic voltage control of the floating diffusion node, switching between a first voltage state during the hold period (to minimize leakage and generation) and a second voltage state during readout (to enable signal transfer). This dynamic approach maintains signal integrity throughout the extended hold time required for global shutter operation across all rows.
Solution Approach 2:
The patent applies preliminary action by pre-setting the floating diffusion node to a specific voltage state before charge transfer operations. By establishing the node at an appropriate voltage level in advance, the system prepares the node to either minimize leakage during hold time or facilitate efficient charge transfer during readout, thereby maintaining signal integrity throughout the extended hold period.
3Ease of operation
If a constant voltage is applied to the floating diffusion node, then circuit operation is simplified, but charge leakage increases during signal hold time
Solution Approach 1:
The patent transitions from a static voltage approach to a dynamic one by implementing a voltage switching mechanism controlled by control signals. The floating diffusion node receives a first voltage during signal hold time (minimizing leakage) and switches to a second voltage during readout operations. This dynamic control, while adding circuit complexity, dramatically reduces charge leakage and improves global shutter efficiency.
Solution Approach 2:
The patent employs feedback through control signals that regulate the voltage state of the floating diffusion node based on the operational phase. The control circuit monitors the operational state (hold time vs. readout) and adjusts the node voltage accordingly, creating a feedback loop that optimizes charge retention while maintaining ease of operation through automated control.
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 design enhances global shutter efficiency by reducing charge leakage, thereby improving image fidelity and reducing image artifacts, especially when capturing high-speed subjects.
Implementation Method 1
a photodiode
Data Source
AI summary
A global shutter compatible pixel circuit comprising a reset gate (RG) transistor is provided in which a dynamic voltage is applied to the drain of the reset gate transistor in order to reduce a floating diffusion (FD) leakage therethrough during signal hold time. The drain voltage of the reset gate transistor is held at a lower voltage than a circuit supply voltage to minimize the off-state leakage through the RG transistor, thus reducing the change in the voltage at the floating diffusion during the signal hold time. In addition, a design structure for such a circuit providing a dynamic voltage to the drain of a reset gate of a pixel circuit is also provided.