Image Sensor Mode Transistor Capacitance Control
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Solution Overview
Problem
Image sensors using the rolling shutter method often result in image distortion due to varying photocharge integration times across different rows of pixels, which the global shutter method aims to mitigate by controlling integration time equally across all pixels.
Innovation Solution
An image sensor design that includes a pixel array with a photodiode, floating diffusion node, sampling transistors, capacitors, and mode transistors, allowing for controlled photocharge integration time across all pixels, enabling operation in both global and rolling shutter modes without distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the rolling shutter method is used to simplify the circuit structure and reduce the number of transistors per pixel, then device complexity is reduced, but image distortion occurs due to varying photocharge integration times across different rows
Solution Approach 1:
The patent implements dynamic control of the photocharge integration time by using a control signal to adjust the integration period. The integration time is dynamically set to match the exposure time of a reference pixel, allowing the system to adapt between rolling and global shutter modes. This dynamic adjustment resolves the contradiction by enabling uniform integration time across all pixels (improving image quality) while maintaining circuit simplicity through controlled dynamic operation.
Solution Approach 2:
The patent changes the integration time parameter of photocharges based on the exposure time of the reference pixel. By adjusting this parameter dynamically, the system can operate in either rolling shutter mode (simpler operation) or global shutter mode (uniform integration time across all pixels). This parameter change allows the system to resolve the contradiction between circuit simplicity and image quality by selecting the appropriate operating mode.
2Manufacturing precision
If the global shutter method is used to eliminate image distortion by controlling integration time equally across all pixels, then image quality is improved, but the circuit structure becomes more complex requiring additional transistors and capacitors
Solution Approach 1:
The patent implements multi-functionality by designing the pixel circuit to operate in both rolling shutter mode and global shutter mode. The same circuit structure can perform either function depending on the control signal, eliminating the need for separate circuits for each mode. This universality resolves the contradiction by achieving global shutter image quality without requiring a completely separate complex circuit design.
Solution Approach 2:
The patent uses dynamic control signals to switch between operating modes. The integration time is dynamically adjusted based on whether rolling or global shutter mode is selected, allowing the circuit to adapt its behavior. This dynamic operation enables the circuit to achieve global shutter performance when needed while maintaining the flexibility to operate in simpler modes when appropriate.
3Adaptability or versatility
If additional transistors and capacitors are added to support global shutter mode, then adaptability is improved, but the number of components per pixel increases
Solution Approach 1:
The patent achieves multi-functionality by designing circuits that can operate in both rolling shutter and global shutter modes using the same components. The pixel array, reference pixel, and associated circuitry serve multiple purposes depending on the control signal. This universality provides adaptability for different shutter modes without proportionally increasing the number of components.
Solution Approach 2:
The patent uses a reference pixel to pre-determine the exposure time before capturing the main image data. This preliminary action allows the system to set the integration time for all pixels based on the reference measurement, enabling global shutter operation without requiring separate control circuits for each pixel. The reference pixel performs the preliminary measurement that guides the subsequent image capture.
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
The solution ensures that the image sensor generates images without distortion by maintaining equal photocharge integration times across all pixels, effectively addressing the issue of varying integration times in rolling shutter methods.
Implementation Method 1
each pixel of the plurality of pixels includes a photodiode; a floating diffusion node configured to integrate photocharges generated in the photodiode
Data Source
AI summary
An image sensor is provided. The image sensor includes a pixel array in which a plurality of pixels are arranged, wherein each of the plurality of pixels includes a photodiode; a floating diffusion node configured to integrate photocharges generated in the photodiode; a first sampling transistor electrically connected to a first node; a first capacitor electrically connected to a first node and configured to store a charge corresponding to a voltage of the floating diffusion node which is reset; a second sampling transistor electrically connected to a second node; a second capacitor electrically connected to the second node and configured to store a charge corresponding to a voltage of the floating diffusion node in which the photocharges are integrated; and at least one mode transistor configured to adjust an equivalent capacitance of each of the first node and the second node according to a mode control signal.