Global Shutter Imaging Pixels With Shared Source Follower Transistor
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Solution Overview
Problem
Conventional global shutter image sensors require two source follower transistors per pixel, which occupies large pixel area, making it desirable to develop improved global shutter pixels with reduced transistor count.
Innovation Solution
Implementing a global shutter mode where each pixel uses a source follower transistor from an adjacent pixel, allowing for simultaneous charge integration and readout with a dummy row of pixels to share transistors, thereby reducing the number of transistors per pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two source follower transistors are used per pixel to implement global shutter functionality, then global shutter operation is achieved, but pixel area increases
Solution Approach 1:
The patent merges the source follower transistor functionality across adjacent pixels by sharing a single source follower transistor between multiple pixels. This is achieved by having multiple pixels share common readout circuitry and charge storage regions, allowing global shutter operation with reduced transistor count per pixel. The shared source follower transistor serves multiple pixels simultaneously, reducing the overall pixel area while maintaining global shutter capability.
Solution Approach 2:
The patent implements multi-functionality by designing pixels that can operate in both global shutter and rolling shutter modes using the same shared source follower transistor and charge storage infrastructure. The charge storage regions and readout circuitry serve universal purposes across multiple pixels and multiple operating modes, eliminating the need for dedicated transistors for each pixel while maintaining versatility.
2Adaptability or versatility
If two source follower transistors are used per pixel, then global shutter operation is achieved, but device complexity increases
Solution Approach 1:
The patent combines the source follower transistor resources across multiple pixels, so that instead of each pixel having its own dedicated source follower transistor, a single source follower transistor is shared among multiple pixels. This merging approach reduces the transistor count per pixel from two to effectively less than one when averaged across the pixel array, simplifying the overall device architecture while maintaining global shutter functionality.
Solution Approach 2:
The patent uses a replicated structure where the shared source follower transistor and charge storage regions are copied across pixel columns or rows, allowing the same circuit architecture to be reused multiple times. This copying approach reduces complexity by avoiding redundant transistor designs in each pixel while maintaining the necessary functionality through systematic replication of the shared circuit elements.
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 approach enables global shutter functionality with reduced pixel area usage, allowing for efficient and simultaneous image capture across all pixels while maintaining effective noise correction through correlated double sampling.
Implementation Method 1
Each pixel includes a photodiode that generates charge in response to incident light
Data Source
AI summary
A global shutter imaging pixel may have a single source follower transistor. The source follower transistor may be coupled to a floating diffusion region and a charge storage region. In order to read out samples from the charge storage region without including a second source follower transistor in each pixel, the samples may be transferred to floating diffusion regions of adjacent pixels. Alternatively, a transistor may be configured to transfer charge from the charge storage region to the floating diffusion region of the same pixel, thus reusing a single source follower transistor. These types of pixels may be used for correlated double sampling, where a reset charge level and integration charge level are both sampled. These pixels may also operate in a global shutter mode where images are captured simultaneously by each pixel.