Split Pixel CMOS Sensor for High Dynamic Range Imaging
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Solution Overview
Problem
Standard image sensors have a limited dynamic range, struggling to capture details in both bright highlights and dim shadows due to their limited ability to handle the wider dynamic range of real-world luminance, which is addressed by incorporating high dynamic range (HDR) technologies.
Innovation Solution
The implementation of a high dynamic range split pixel CMOS image sensor with embedded split-diode structures, featuring a small photodiode for bright light and a large photodiode for dimmer or medium intensity lighting, along with an attenuating layer and multiple floating diffusions to reduce color crosstalk and enhance dynamic range capture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standard image sensor is used, then the device complexity is low, but the dynamic range is limited to 60-70 dB
Solution Approach 1:
Each pixel is divided into multiple photodiodes with different areas (small, medium, large) that capture light at different intensity levels. This segmentation allows simultaneous capture of highlights and shadows within a single exposure, achieving high dynamic range without requiring multiple exposures or complex post-processing
Solution Approach 2:
Different regions within each pixel have different photodiode areas optimized for different light intensities. Small photodiodes capture bright highlights, medium photodiodes capture mid-tones, and large photodiodes capture dim shadows. This local differentiation of quality enables the sensor to handle the full luminance range of natural scenes (90 dB and greater)
2Reliability
If multiple photodiodes are integrated in each pixel for HDR, then the dynamic range increases, but color crosstalk increases
Solution Approach 1:
Color information is extracted and assigned to specific photodiodes based on their optimal performance range. Small photodiodes are assigned to capture highlights, medium photodiodes capture mid-tones, and large photodiodes capture shadows. This extraction and selective assignment of color information to appropriate photodiodes minimizes color crosstalk while maintaining HDR capability
Solution Approach 2:
A microlens array is introduced as an intermediary element that focuses incident light onto the appropriate photodiode within each pixel. The microlenses act as mediators that direct light from bright areas to small photodiodes, medium-intensity light to medium photodiodes, and dim light to large photodiodes, thereby reducing color crosstalk between different photodiode types
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 enables the capture of a wider dynamic range, effectively reducing color crosstalk and improving the ability to render images with both bright and dark areas, thereby enhancing the imaging capabilities of image sensors.
Implementation Method 1
The image sensor includes an array of pixels having photosensitive elements (e.g., photodiodes) that absorb a portion of the incident image light and generate image charge upon absorption of the image light
Data Source
AI summary
A pixel cell includes a plurality of subpixels to generate image charge in response to incident light. The subpixels include an inner subpixel laterally surrounded by outer subpixels. A first plurality of transfer gates disposed proximate to the inner subpixel and a first grouping of outer subpixels. A first floating diffusion is coupled to receive the image charge from the first grouping of outer subpixels through a first plurality of transfer gates. A second plurality of transfer gates disposed proximate to the inner subpixel and the second grouping of outer subpixels. A second floating diffusion disposed in the semiconductor material and coupled to receive the image charge from each one of the second grouping of outer subpixels through the second plurality of transfer gates. The image charge in the inner subpixel is received by the first, second, or both floating diffusions through respective transfer gates.