Image Sensor Pixel with Multiple Storage Nodes for HDR
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Solution Overview
Problem
Current image sensors face challenges in capturing high dynamic range (HDR) images efficiently, particularly when dealing with moving subjects, as they require consecutive image captures which are time-consuming and consume significant semiconductor real estate due to the use of multiple photodiodes.
Innovation Solution
The implementation of pixels with multiple storage nodes, including a global shutter gate, transfer storage gates, and floating diffusion, allows for the rapid capture and storage of multiple image charges using a single photodiode, enabling HDR image generation without the limitations of readout time and reducing transistor count, thereby increasing quantum efficiency and imaging capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two photodiodes are used in a combination pixel to capture HDR images, then HDR capability is achieved, but semiconductor real estate is significantly consumed
Solution Approach 1:
The pixel is segmented into multiple storage nodes (first storage node, second storage node, third storage node) that can independently store image charges from different exposure times. This allows a single photodiode to capture multiple temporal snapshots by transferring charges to different storage nodes at different times, achieving HDR functionality without requiring multiple photodiodes simultaneously.
Solution Approach 2:
The patent transitions from spatial multiplexing (multiple photodiodes capturing different exposure levels simultaneously) to temporal multiplexing (single photodiode capturing charges at different times and storing in separate nodes). This dimensional shift from space to time allows HDR capture with a single photodiode, reducing area consumption while maintaining functionality.
2Adaptability or versatility
If consecutive images are captured to generate HDR, then HDR images are produced, but readout time impacts image quality especially with moving subjects
Solution Approach 1:
Multiple image charges from different exposure times are pre-captured and stored in separate storage nodes within the same pixel during the exposure sequence. The first image charge is stored in the first storage node, the second in the second storage node, and the third in the third storage node. This preliminary storage eliminates the need for sequential readout operations, allowing all stored charges to be read out simultaneously later, thus eliminating readout time delays that would otherwise impact image quality of moving subjects.
3Adaptability or versatility
If multiple photodiodes are used for HDR capture, then different light levels are sensed, but transistor count increases reducing quantum efficiency
Solution Approach 1:
A single photodiode is made multi-functional by enabling it to capture and store multiple image charges from different exposure times in separate storage nodes. The photodiode serves multiple purposes: capturing bright light conditions, low light conditions, and intermediate light conditions at different times, replacing the need for multiple specialized photodiodes and their associated transistors, thus reducing overall device complexity while maintaining versatile light level sensing capability.
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 the capture of HDR images with reduced motion artifacts and increased performance by allowing simultaneous or rapid sequential image capture without the constraints of readout speed, while also minimizing the size and power consumption of the image sensor.
Implementation Method 1
A pixel array includes a first pixel. The first pixel includes a photodiode
Data Source
AI summary
An image sensor pixel includes a photodiode, a first storage node, a second storage node, a first transfer storage gate, a second transfer storage gate, a floating diffusion, and an output gate. The photodiode is for generating image charge in response to image light. The first storage node, the second storage node, and the photodiode have a first doping polarity. The first transfer storage gate is coupled to transfer the image charge from the photodiode to the first storage node. The first transfer storage gate is disposed over a majority portion of the first storage node. The second transfer storage gate is coupled to transfer the image charge from the first storage node to the second storage node. The second transfer storage gate is disposed over a majority portion of the second storage node. The output gate transfers the image charge from the second storage node to the floating diffusion.