Image Sensor Pixel Homogeneous Photodiodes High Dynamic Range
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Solution Overview
Problem
High dynamic range image sensors face challenges in efficiently processing image signals from different photodiodes due to physical and electrical differences, leading to complex and less efficient readout electronics.
Innovation Solution
A high dynamic range imaging system with a pixel array comprising two photodiodes, one for low light and one for bright light, sharing a floating diffusion and transfer transistors, allowing separate image charge transfer and amplification, and using microlenses and aperture sizers to optimize light exposure and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If separate photodiodes are used for bright and low light conditions, then dynamic range is improved, but device complexity increases due to different physical and electrical characteristics
Solution Approach 1:
The patent applies homogeneity by designing both photodiodes with identical physical and electrical characteristics, including matching doping concentrations, geometric dimensions, and full well capacities. This uniformity allows the same readout electronics to process signals from both photodiodes, resolving the complexity issue while maintaining the extended dynamic range capability through dual photodiode operation.
2Measurement precision
If different photodiodes are used for different lighting conditions, then sensitivity to specific light levels is improved, but manufacturing precision requirements increase
Solution Approach 1:
By making both photodiodes identical in structure, doping, and dimensions, the patent reduces manufacturing precision requirements. The same fabrication process can be used for both photodiodes, ensuring consistent characteristics without requiring complex matching procedures, while still achieving differentiated sensitivity through optical design elements like microlenses and aperture sizers.
3Device complexity
If shared readout electronics are used for both photodiodes, then device complexity is reduced, but signal processing accuracy may be compromised
Solution Approach 1:
The patent ensures that shared readout electronics can accurately process signals from both photodiodes by making the photodiodes themselves homogeneous in electrical characteristics. This includes matching output impedance, signal amplitude ranges, and noise characteristics, allowing a single readout circuit to handle both bright and low light signals with equal accuracy.
Solution Approach 2:
The patent uses parameter changes in the optical path (microlens focus, aperture size) rather than electrical parameters to differentiate the photodiode responses. This allows the electrical characteristics to remain identical, enabling shared readout electronics to process both signals accurately without requiring complex signal conditioning circuits.
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 simplifies signal processing by maintaining similar full well capacities for both photodiodes, reducing complexity and enhancing sensitivity, enabling efficient capture and combination of low and bright light image data into a single HDR image.
Implementation Method 1
a first photodiode to capture low light data and a second photodiode to capture bright light data
Data Source
AI summary
An image sensor pixel includes a first photodiode and a second photodiode disposed in a semiconductor material. The first photodiode has a first doped region, a first lightly doped region, and a first highly doped region. The second photodiode has a second full well capacity substantially equal to a first full well capacity of the first photodiode, and includes a second doped region, a second lightly doped region, and a second highly doped region. The image sensor pixel also includes a first microlens optically coupled to direct a first amount of image light to the first photodiode, and a second microlens optically coupled to direct a second amount of image light to the second photodiode. The first amount of image light is larger than the second amount of image light.