CMOS Image Sensor Pixel Array Segmentation for Dynamic Range
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Solution Overview
Problem
CMOS image sensors face challenges with reduced pixel photosensitivity and dynamic range due to miniaturization, particularly in absorbing long-wavelength light, leading to issues like spatial distortion in rolling shutter mode and insufficient dynamic range for capturing scenes with both bright and dark areas.
Innovation Solution
An image sensor pixel array is designed with two types of pixels: one with an opaque light-blocking layer and another without, where the light-blocking layer has a shading rate greater than 98%, allowing for increased dynamic range by collecting scattered light, thereby enhancing High Dynamic Range (HDR) imaging and mitigating light flicker.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is miniaturized to increase resolution, then resolution is improved, but photosensitivity and dynamic range deteriorate
Solution Approach 1:
The pixel array is segmented into two distinct types: first pixels with light-blocking layers for collecting scattered light from bright areas, and second pixels without light-blocking layers for capturing direct light from dark areas. This segmentation allows each pixel type to be optimized for specific lighting conditions, maintaining photosensitivity despite overall miniaturization.
Solution Approach 2:
Different regions of the pixel array have different optical properties. First pixels have light-blocking layers that scatter light into the pixel, while second pixels have no light-blocking layers to maximize direct light absorption. This local differentiation of optical quality enables the system to maintain high photosensitivity in both bright and dark regions simultaneously.
2Measurement precision
If pixel size is miniaturized, then resolution is improved, but dynamic range deteriorates
Solution Approach 1:
The pixel array is divided into two functional segments: first pixels with light-blocking layers optimized for capturing scattered light from highlights, and second pixels without light-blocking layers optimized for direct light from shadows. This segmentation enables the sensor to maintain wide dynamic range despite miniaturization by having specialized pixels for different luminance ranges.
Solution Approach 2:
Different local regions have different optical structures adapted to their function. First pixels have light-blocking layers that create scattering paths for extended dynamic range, while second pixels have open structures for maximum light collection. This local optimization of optical quality preserves dynamic range capability in miniaturized pixels.
3Ease of manufacture
If BSI technology is used with thin substrate, then manufacturing is simplified, but absorption of long-wavelength light deteriorates
Solution Approach 1:
Light-blocking layers act as intermediary structures that scatter long-wavelength light within the thin substrate, increasing the effective optical path length. This intermediary scattering mechanism compensates for the insufficient substrate thickness in BSI technology, enabling adequate absorption of red and other long-wavelength light while maintaining manufacturing simplicity.
4Device complexity
If rolling shutter mode is used, then readout is simplified, but spatial distortion increases
Solution Approach 1:
The pixel array itself generates reference signals through the scattered light collection in first pixels, eliminating the need for external reference measurements. The scattered light signals from first pixels serve as self-referenced data that can be used to correct spatial distortion artifacts inherent in rolling shutter readout, maintaining simple readout while reducing distortion.
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 effectively increases the dynamic range of the image sensor, allowing for better capture of both highlights and shadows without saturation, and provides light flicker mitigation, while maintaining a simple manufacturing process and reducing costs.
Implementation Method 1
The first type of pixel includes an opaque or light-blocking layer in the illumination path
Implementation Method 2
illumination is blocked and light scattered from an adjacent pixel is collected
Implementation Method 3
One way light may be scattered into the first type pixel into the second type of pixel is by diffraction
Data Source
AI summary
A CMOS image sensor with an imaging array of pixels containing selected pixels wherein illumination is blocked and light scattered from an adjacent pixel is collected. The signal from the selected pixels is resilient against saturation and thereby contributes to increased dynamic range of the imaging signal. The image sensor may be incorporated within a digital camera.