HDR Imaging Pixel Overflow Capacitors for Dynamic Range Control
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Solution Overview
Problem
Conventional image sensors face limitations in high dynamic range operation, resulting in lower than desired resolution, sensitivity, and higher noise levels, especially when attempting to capture images with varying light conditions.
Innovation Solution
The implementation of imaging pixels with an overflow capacitor and a charge directing structure that intermittently directs excess charge to a secondary overflow capacitor, allowing for extended dynamic range by controlling the overflow paths and integration times, thereby enhancing the sensor's ability to handle high incident light levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional image sensors use alternate rows with different integration times for HDR operation, then dynamic range is improved, but resolution and sensitivity deteriorate while noise levels increase
Solution Approach 1:
The pixel is segmented into multiple independent charge storage regions (first overflow capacitor and second overflow capacitor) that can be independently controlled. This segmentation allows different integration times to be applied to different storage regions within the same pixel, rather than requiring separate pixels or rows for different integration times, thereby maintaining spatial resolution while achieving HDR capability.
Solution Approach 2:
The patent adds a temporal dimension to charge storage by implementing multiple overflow capacitors that can be activated at different times during the integration period. This allows the system to capture multiple exposure levels within a single pixel over time, achieving HDR without sacrificing spatial resolution by utilizing the time dimension rather than requiring spatial separation of pixels.
2Adaptability or versatility
If conventional image sensors use alternate rows with different integration times for HDR operation, then dynamic range is improved, but sensitivity deteriorates
Solution Approach 1:
By segmenting the charge storage into multiple capacitors within each pixel, the system can allocate different storage regions to different sensitivity requirements. The first overflow capacitor can be optimized for shorter integration times (higher sensitivity to rapid changes), while the second overflow capacitor handles longer integration times (lower sensitivity, higher dynamic range), thereby maintaining overall sensitivity while achieving extended dynamic range.
Solution Approach 2:
The pixel circuit is pre-configured with multiple overflow capacitors and the necessary switching infrastructure before image capture. This preliminary setup allows the system to rapidly switch between different integration modes without losing sensitivity, as the charge paths are already established and can be activated immediately when needed, rather than requiring physical movement or reconfiguration during operation.
3Adaptability or versatility
If conventional image sensors use alternate rows with different integration times for HDR operation, then dynamic range is improved, but noise levels increase
Solution Approach 1:
Segmenting charge storage into multiple capacitors allows the system to isolate and manage noise sources more effectively. Each capacitor can be independently reset and managed, preventing noise accumulation that would occur in a single large storage region. The segmented architecture enables selective readout of only the necessary charge portions, reducing the impact of thermal noise and other harmful factors.
Solution Approach 2:
The multiple overflow capacitors act as intermediaries between the photodiode and the readout circuitry. These intermediate storage regions allow for controlled charge transfer and can be independently managed to minimize noise propagation. The system can choose to read from the capacitor with the optimal signal-to-noise ratio for the given lighting conditions, thereby reducing overall noise levels while maintaining dynamic range capability.
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 solution improves the dynamic range of image sensors, reducing noise and increasing sensitivity while maintaining or improving signal-to-noise ratio, effectively addressing the limitations of conventional HDR image sensors.
Implementation Method 1
Typical image pixels contain a photodiode for generating charge in response to incident light
Data Source
AI summary
A high dynamic range imaging pixel may include a photodiode that generates charge in response to incident light. When the generated charge exceeds a first charge level, the charge may overflow through a first transistor to a first storage capacitor. When the generated charge exceeds a second charge level that is higher than the first charge level, the charge may overflow through a second transistor. The charge that overflows through the second transistor may alternately be coupled to a voltage supply and drained or transferred to a second storage capacitor for subsequent readout. Diverting more overflow charge to the voltage supply may increase the dynamic range of the pixel. The amount of charge diverted to the voltage supply may therefore be updated to control the dynamic range of the imaging pixel.