Split Photodiode Image Sensor Pixels for High Dynamic Range
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Solution Overview
Problem
Conventional image sensors often produce images with artifacts due to low dynamic range, leading to overexposure or underexposure in scenes with both bright and dark portions, and high dynamic range techniques can introduce motion artifacts, especially in dynamic scenes with non-static objects.
Innovation Solution
The implementation of image sensor pixels with multiple symmetrically arranged photodiodes and a shared floating diffusion region, allowing for dual conversion gain modes and efficient charge transfer, which enables high dynamic range imaging without motion artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional single photodiode pixels are used, then device complexity is low, but dynamic range is limited causing overexposure or underexposure artifacts
Solution Approach 1:
The pixel is divided into multiple photodiodes (first photodiode and second photodiode) with different photosensitive areas. The first photodiode has a larger photosensitive area for capturing bright scenes, while the second photodiode has a smaller photosensitive area for capturing dark scenes. This segmentation allows simultaneous capture of both bright and dark portions of a scene without overexposure or underexposure artifacts.
2Illumination intensity
If multiple images with different exposure times are captured for HDR, then dynamic range is improved, but motion artifacts are introduced in dynamic scenes
Solution Approach 1:
The pixel performs preliminary action by simultaneously generating charge in multiple photodiodes with different photosensitive areas during a single exposure time. The first photodiode generates charge for bright portions while the second photodiode generates charge for dark portions at the same time, eliminating the need for multiple captures with different exposure times and thus avoiding motion artifacts in dynamic scenes.
3Illumination intensity
If multiple images are captured and combined for HDR, then dynamic range is improved, but processing time and complexity increase
Solution Approach 1:
The pixel performs preliminary action by simultaneously generating charge in multiple photodiodes with different photosensitive areas during a single exposure time. The first photodiode generates charge for bright portions while the second photodiode generates charge for dark portions at the same time, eliminating the need for multiple captures with different exposure times and thus avoiding motion artifacts in dynamic scenes.
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 improves image sensor performance by reducing noise and dark current, enabling accurate capture of scenes with varying light conditions without introducing motion artifacts, thus enhancing the quality of captured images.
Implementation Method 1
Typical image pixels contain a photodiode for generating charge in response to incident light
Data Source
AI summary
An imaging device may have an array of image sensor pixels. Each image sensor pixel of the array of image sensor pixels may have split photodiodes that are symmetric about a shared floating diffusion region. The floating diffusion region may be coupled to each of the photodiodes. Each of the split photodiodes and the floating diffusion region may generate charge in response to light incident on the image sensor pixel. The split photodiodes and the floating diffusion region may be covered by a microlens. The charge generated by the photodiodes and the floating diffusion region may be compared and utilized by the imaging device in phase detection applications. The image sensor pixel may also include a dual conversion gain capacitor and a gain select transistor to produce high dynamic range (HDR) images.