Dual Photodiode Image Sensor Pixel for High Dynamic Range
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Solution Overview
Problem
High dynamic range image sensors face challenges in achieving a wide range of lighting conditions due to physical and electrical differences between sub-pixels, leading to complex and inefficient signal processing.
Innovation Solution
Implementing HDR pixels with two photodiodes, where one photodiode captures low light and the other captures bright light, using shared floating diffusion and transfer transistors with separate control signals, and employing identical microlenses and filters to maintain equal full well capacities and simplify signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If physical and electrical differences are introduced between sub-pixels to sense different lighting conditions, then the dynamic range is improved, but the device complexity increases
Solution Approach 1:
The pixel is segmented into two distinct photodiodes: a first photodiode for capturing low-light conditions and a second photodiode for capturing bright light conditions. Each photodiode has optimized characteristics for its specific lighting range, allowing the sensor to handle a wide dynamic range while maintaining simplicity through functional separation rather than complex processing requirements.
2Adaptability or versatility
If physical and electrical differences are introduced between sub-pixels to sense different lighting conditions, then the dynamic range is improved, but the processing complexity increases
Solution Approach 1:
Both photodiodes share identical full well capacities and are read out through a common readout circuit, creating homogeneity in the processing path. This design choice simplifies signal processing by eliminating the need for complex compensation algorithms that would be required if the photodiodes had different electrical characteristics, while still maintaining the ability to capture different lighting conditions.
3Adaptability or versatility
If different photodiodes are used for bright and low light conditions, then the dynamic range is improved, but the readout electronics complexity increases
Solution Approach 1:
The readout circuitry is merged into a shared configuration where both the first and second photodiodes connect to a common readout path. This combining approach allows the sensor to maintain high dynamic range capability through dual photodiodes while simplifying the readout electronics by eliminating the need for separate readout circuits for each photodiode type.
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 allows for simpler and more efficient signal processing, reducing complexity and increasing accuracy, enabling faster and cheaper processing of HDR images across varying lighting conditions.
Implementation Method 1
One sub-pixel can be used to sense bright light conditions while another sub-pixel can be used to sense low light conditions
Data Source
AI summary
An image sensor pixel includes a first photodiode, a second photodiode, a first microlens, a second microlens, and a filter. The first and second photodiode are disposed adjacent to each other in a semiconductor material. The first photodiode has a first full well capacity that is substantially equal to a second full well capacity of the second photodiode. The first microlens is disposed over the first photodiode and the second microlens is disposed over the second photodiode. The second microlens is substantially identical to the first microlens. The filter is disposed between the second microlens and the second photodiode to reduce an intensity of the image light incident upon the second photodiode. The filter does not substantially affect the image light directed toward the first photodiode.