RGBZ Pixel Cell Unit for Image Sensor Wavelength Discrimination
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Solution Overview
Problem
Current image sensor technologies face challenges in optimizing the layout of RGBZ pixel unit cells to enhance optical sensitivity while accommodating the different capacitance requirements for visible light and infrared detection, leading to trade-offs in semiconductor surface area usage and noise levels.
Innovation Solution
The implementation of a shared storage capacitor for visible light pixels and a separate larger storage capacitor for the Z pixel, allowing for sequential readouts and optimized transistor placement to balance optical sensitivity and noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional RGB pixel cell structure is used, then the device complexity is low, but the measurement precision and signal-to-noise ratio are insufficient due to inability to distinguish same-color photons from different wavelengths
Solution Approach 1:
The pixel cell is divided into multiple functional regions: a first photoelectric conversion region with first color filter for capturing first-wavelength light, and a second photoelectric conversion region with second color filter for capturing second-wavelength light. This segmentation allows the system to distinguish between different wavelengths of light while maintaining a relatively simple overall structure.
Solution Approach 2:
Different regions of the pixel cell are assigned different functional properties: the first photoelectric conversion region is optimized for detecting first-wavelength light with corresponding color filter, while the second region is optimized for second-wavelength light. This local differentiation enables wavelength-specific detection without requiring complete structural redesign of the entire pixel cell.
2Measurement precision
If multiple photoelectric conversion regions with different color filters are implemented, then the wavelength discrimination capability is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The pixel cell is divided into multiple functional regions: a first photoelectric conversion region with first color filter for capturing first-wavelength light, and a second photoelectric conversion region with second color filter for capturing second-wavelength light. This segmentation allows the system to distinguish between different wavelengths of light while maintaining a relatively simple overall structure.
Solution Approach 2:
The pixel cell structure is designed to perform multiple functions within a unified framework: both photoelectric conversion regions share common structural elements and processing steps, allowing the system to detect multiple wavelengths simultaneously while using standardized manufacturing processes that reduce precision requirements.
3Loss of information
If conventional color filter arrays are used, then the device complexity is low, but the loss of information occurs due to inability to differentiate photons of same color but different wavelengths
Solution Approach 1:
The pixel cell is divided into multiple functional regions: a first photoelectric conversion region with first color filter for capturing first-wavelength light, and a second photoelectric conversion region with second color filter for capturing second-wavelength light. This segmentation allows the system to distinguish between different wavelengths of light while maintaining a relatively simple overall structure.
Solution Approach 2:
The invention adds a spatial dimension to wavelength discrimination by creating vertically stacked or laterally arranged photoelectric conversion regions at different positions within the pixel cell. This dimensional arrangement allows simultaneous capture of multiple wavelength bands without requiring complex spectral analysis, preserving wavelength information through spatial separation.
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 configuration enhances optical sensitivity for visible light pixels while increasing infrared detection capacity, allowing for simultaneous or sequential generation of RGB and Z pixel values with reduced noise and extended exposure times.
Implementation Method 1
a first photoelectric conversion unit configured to convert first-wavelength light into a first electrical signal
Implementation Method 2
a second photoelectric conversion unit configured to convert second-wavelength light into a second electrical signal
Data Source
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AI summary
An image sensor is described. The image sensor includes a pixel array having a unit cell that includes visible light photodiodes and an infra-red photodiode. The visible light photodiodes and the infra-red photodiode are coupled to a particular column of the pixel array. The unit cell has a first capacitor coupled to the visible light photodiodes to store charge from each of the visible light photodiodes. The unit cell having a readout circuit to provide the first capacitor's voltage on the particular column. The unit cell having a second capacitor that is coupled to the infra-red photodiode through a transfer gate transistor to receive charge from the infra-red photodiode during a time-of-flight exposure. The unit cell has a back-drain transistor coupled to the infra-red photodiode.