Adaptive Pixel Sensor Exposure for High Dynamic Range Imaging
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Solution Overview
Problem
Current image sensors face challenges in achieving high dynamic range and efficient global shutter operations due to limitations in quantization operations and power consumption, particularly when dealing with high-intensity light, which affects the accuracy of 2D and 3D imaging and introduces non-linearity in light intensity measurements.
Innovation Solution
The implementation of a pixel cell design that includes multiple photodiodes sharing an ADC, with a controller managing exposure periods and quantization operations to perform time-to-saturation, floating diffusion ADC, and pinned photodiode ADC operations, allowing for dynamic adjustment of exposure periods and sharing of quantization resources to improve linearity and dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a single ADC is used for quantization operations in each pixel cell, then power consumption is reduced, but measurement precision deteriorates due to quantization errors and non-linearity
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the exposure time based on detected light intensity levels. When high-intensity light is detected, the exposure time is reduced to prevent saturation and maintain measurement linearity. This allows the use of a single ADC while preserving measurement precision across varying light conditions by adapting the exposure parameter rather than using multiple ADCs with different characteristics.
2Measurement precision
If multiple ADCs are used for quantization operations in each pixel cell, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent segments the quantization process into multiple stages: a first quantization operation for high-intensity light detection and a second quantization operation for low-intensity light detection. This segmentation allows a single ADC to perform different quantization tasks at different exposure times, achieving the precision benefits of multiple ADCs while consuming the power of only one ADC.
Solution Approach 2:
The patent implements periodic action through dual quantization operations where the ADC alternates between different quantization modes. The first quantization operation is performed during a first exposure period for high-intensity light, and the second quantization operation is performed during a second exposure period for low-intensity light. This periodic switching allows precise measurement across different light levels while maintaining low power consumption.
3Measurement precision
If exposure time is extended to capture low-intensity light, then measurement precision for low light is improved, but dynamic range deteriorates due to saturation in high-intensity regions
Solution Approach 1:
The patent applies dynamics by making the exposure time adaptive rather than fixed. The system dynamically adjusts the exposure time based on the detected light intensity: using a longer exposure time for low-intensity light to improve precision, and a shorter exposure time for high-intensity light to prevent saturation. This dynamic adjustment enables the system to maintain both high precision in low light and broad dynamic range across all lighting conditions.
4Adaptability or versatility
If exposure time is reduced to prevent saturation, then dynamic range is improved, but measurement precision for low-intensity light deteriorates
Solution Approach 1:
The patent uses periodic action by implementing two distinct quantization operations with different exposure times. The first quantization operation uses a shorter exposure period to capture high-intensity light without saturation, while the second quantization operation uses a longer exposure period to capture low-intensity light with high precision. The system periodically switches between these operations based on light intensity, thereby achieving both broad dynamic range and high precision across all conditions.
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 enhances the dynamic range and linearity of light intensity measurements, improves shutter efficiency, and reduces power consumption, enabling high-speed imaging and reduced motion blurring while maintaining high frame rates.
Implementation Method 1
A typical pixel in an image sensor includes a photodiode to sense incident light by converting photons into charge (e.g., electrons or holes)
Data Source
AI summary
In one example, a method comprises: exposing a first photodiode to incident light to generate first charge; exposing a second photodiode to the incident light to generate second charge; converting, by a first charge sensing unit, the first charge to a first voltage; converting, by a second charge sensing unit, the second charge to a second voltage; controlling an ADC to detect, based on the first voltage, that a quantity of the first charge reaches a saturation threshold, and to measure a saturation time when the quantity of the first charge reaches the saturation threshold; stopping the exposure of the first photodiode and the second photodiode to the incident light based on detecting that the quantity of the first charge reaches the saturation threshold; and controlling the ADC to measure, based on the second voltage, a quantity of the second charge generated by the second photodiode before the exposure ends.