Stacked CMOS Image Sensor Dual Conversion Gain HDR
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Solution Overview
Problem
Standard image sensors have a limited dynamic range, which cannot capture the full luminance range of natural scenes, requiring multiple exposures to achieve high dynamic range (HDR) imaging, resulting in decreased overall image resolution and issues like ghosting and light flickering.
Innovation Solution
A color pixel array with a dual conversion gain circuit in a stacked architecture, where each pixel circuit includes a photodiode, floating diffusion, transfer transistor, and dual floating diffusion transistor, allowing for high or low conversion gain selection digitally, enabling simultaneous capture of bright and dark objects in a single exposure without multiple exposures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple exposures are used to achieve HDR imaging, then dynamic range is improved, but image resolution deteriorates
Solution Approach 1:
The pixel array is divided into multiple pixel circuits, where each pixel circuit is further segmented into multiple photodetectors (first photodetector, second photodetector, etc.). Each photodetector captures light with different exposure characteristics, enabling multiple exposures to be captured simultaneously within a single pixel circuit, thereby maintaining full resolution while achieving HDR imaging
Solution Approach 2:
The patent transitions from temporal multiplexing (multiple exposures at different times) to spatial multiplexing (multiple photodetectors within the same pixel circuit capturing different exposure levels simultaneously). This dimensional change allows simultaneous capture of multiple exposure images without reducing spatial resolution
2Adaptability or versatility
If multiple exposures are used to achieve HDR imaging, then dynamic range is improved, but ghosting and light flickering occur
Solution Approach 1:
The patent implements preliminary action by having multiple photodetectors within each pixel circuit simultaneously capture different exposure levels of the same scene at the same moment. This simultaneous capture eliminates the temporal separation between exposures, preventing ghosting effects caused by moving objects and light flickering that occur when exposures are taken at different times
Solution Approach 2:
The patent merges multiple exposure images captured by different photodetectors within the same pixel circuit into a single HDR image. By combining the simultaneously captured exposure data from multiple photodetectors, the system achieves HDR imaging without the artifacts (ghosting and flickering) that result from merging sequentially captured images
3Ease of manufacture
If standard image sensor architecture is used, then manufacturing simplicity is maintained, but dynamic range is limited
Solution Approach 1:
Each pixel circuit is segmented into multiple photodetectors with different exposure characteristics, allowing the sensor to capture a wider dynamic range. This segmentation is implemented within the existing CMOS pixel circuit architecture, maintaining compatibility with standard manufacturing processes while enhancing functional capabilities
Solution Approach 2:
The patent implements multi-functionality by enabling each pixel circuit to perform both standard single-exposure imaging and HDR imaging simultaneously through its multiple photodetectors. The pixel array can operate in different modes (standard imaging mode or HDR mode) depending on scene requirements, providing universal functionality without requiring separate specialized sensors
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 solution allows for HDR imaging with improved resolution and elimination of ghosting and light flickering, as pixel values with different conversion gains can be output in a single integration time, capturing a wide dynamic range without the need for multiple exposures.
Implementation Method 1
a photodiode, floating diffusion, transfer transistor, and dual floating diffusion transistor
Data Source
AI summary
A pixel circuit for use in a high dynamic range (HDR) image sensor includes a photodiode and a floating diffusion is disposed in the first semiconductor wafer. A transfer transistor is disposed in the first semiconductor wafer and is adapted to be switched on to transfer the charge carriers photogenerated in the photodiode to the floating diffusion. An in-pixel capacitor is disposed in a second semiconductor wafer. The first semiconductor wafer is stacked with and coupled to the second semiconductor wafer. A dual floating diffusion (DFD) transistor is disposed in the first semiconductor wafer. The in-pixel capacitor is selectively coupled to the floating diffusion through the DFD transistor. The floating diffusion is set to low conversion gain in response to the in-pixel capacitor being coupled to the floating diffusion, and high conversion gain in response to the in-pixel capacitor being decoupled from the floating diffusion.