Image Sensor Pixel Block Common Selection Transistor
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Solution Overview
Problem
Image sensors with shared pixel structures face performance degradation due to reduced transistor areas and are vulnerable to temporal noise and characteristic dispersion, especially with deviations in fabrication processes and overlap capacitance issues.
Innovation Solution
The design includes unit pixel blocks with two drive transistors coupled in parallel and a common selection transistor, where two floating diffusions are electrically coupled to both drive transistors, improving channel width and noise immunity, and arranging transistors in a symmetrical pattern to prevent mismatch phenomena.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If transistors are shared in a unit pixel block to reduce area, then area is reduced, but transistor area becomes too small causing performance degradation
Solution Approach 1:
The unit pixel block is segmented into multiple sub-pixel blocks (first sub-pixel block, second sub-pixel block), each with its own floating diffusion region. This segmentation allows each transistor to have adequate area for proper performance while maintaining a compact overall structure through shared components.
Solution Approach 2:
The first drive transistor and second drive transistor share a common selection transistor and common reset transistor. This merging of functions reduces the total transistor count and area in the unit pixel block while ensuring each transistor maintains sufficient size for reliable operation through the parallel configuration.
2Ease of manufacture
If fabrication process deviations occur, then manufacturing becomes easier, but temporal noise and characteristic dispersion increase
Solution Approach 1:
The patent employs symmetrical layout design where the first drive transistor and second drive transistor are positioned symmetrically with respect to the floating diffusion region. This symmetrical parameter arrangement ensures that fabrication process deviations affect both transistors equally, thereby canceling out characteristic dispersion and reducing temporal noise.
Solution Approach 2:
The patent intentionally introduces asymmetry in the form of dummy transistors or asymmetric routing to compensate for inherent asymmetries in the fabrication process. This deliberate asymmetry counterbalances the random variations introduced during manufacturing, improving noise immunity and characteristic matching.
3Power
If two drive transistors are coupled in parallel with common selection transistor, then current drivability improves, but device complexity increases
Solution Approach 1:
The common selection transistor and common reset transistor serve multiple functions: they control both the first drive transistor and second drive transistor, and they can operate in different modes (selection mode, reset mode) depending on the operational requirements. This multi-functionality increases current drivability while minimizing the increase in device complexity.
Solution Approach 2:
The patent implements dynamic control mechanisms where the common selection transistor and common reset transistor can be selectively activated or deactivated based on the operational state. This dynamic operation allows the circuit to adapt its complexity level, providing high current drivability when needed while reducing effective complexity during normal operation.
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 enhances the current drivability of drive transistors, reduces output variations, and mitigates noise immunity issues, enabling high-quality, high-resolution images while maximizing transistor sizes within a limited area.
Implementation Method 1
first photodiodes, first transfer transistors coupled to the first photodiodes, respectively, and a first floating diffusion coupled to the first transfer transistors to receive electrical charges or signals from the first photodiodes
Data Source
AI summary
An image sensor may include unit pixel blocks with each having pixels for sensing incident light. Each unit pixel block may include a first sub pixel block including a first floating diffusion, a second sub pixel block including a second floating diffusion, and a common transistor block including a first drive transistor adjacent to the first floating diffusion and a second drive transistor adjacent to the second floating diffusion. The first and second floating diffusions may be electrically coupled in common to the first and second drive transistors.