In-Frame Multi-Bit Exposure Control for High Dynamic Range Image Sensors
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Solution Overview
Problem
Conventional image sensors, particularly CMOS sensors, face challenges in achieving high dynamic range imaging due to limited well-capacity and fixed exposure times, making it difficult to perform effectively across a wide range of lighting conditions.
Innovation Solution
The implementation of a high dynamic range image sensor with a programmable exposure control and read-out architecture using pixel-level hybrid bonding, where each pixel circuit has multi-bit exposure control and memory for optimal operation, allowing for individual in-frame exposure control and improved charge integration across the pixel array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple successive exposures are used to achieve HDR, then dynamic range is improved, but frame rate and temporal resolution deteriorate
Solution Approach 1:
The patent pre-charges specific pixel rows before they are read out, allowing these pixels to integrate charge for multiple exposure periods simultaneously. This preliminary charge integration action enables multi-exposure HDR data to be captured in parallel rather than through sequential multi-frame exposures, thereby maintaining high frame rates while achieving extended dynamic range.
Solution Approach 2:
The patent introduces a temporal dimension to the charge integration process by allowing pixels to accumulate charge over multiple exposure periods before readout. This transforms the traditional single-exposure spatial sampling into a multi-exposure temporal integration process, enabling HDR capture without sacrificing frame rate through the use of in-frame multi-bit exposure control.
2Measurement precision
If pixel circuits are made smaller to increase resolution, then spatial resolution is improved, but well-capacity and dynamic range deteriorate
Solution Approach 1:
The patent pre-charges selected pixel rows before readout, enabling these small pixel circuits to integrate charge over extended periods. This preliminary charge accumulation allows pixels with limited well-capacity to effectively capture a wider dynamic range by accumulating charge from multiple exposure periods before being read out, thus compensating for their smaller size.
Solution Approach 2:
The patent implements dynamic exposure control where different pixel rows can have different exposure durations and timing. This dynamic approach allows the system to optimize charge integration time for each row based on lighting conditions, enabling small pixel circuits to achieve effective HDR performance through variable exposure timing rather than being constrained by their fixed, small well-capacity.
3Device complexity
If fixed exposure times are used in conventional CMOS sensors, then circuit simplicity is maintained, but adaptability to varying lighting conditions deteriorates
Solution Approach 1:
The patent segments the pixel array into multiple rows with independent exposure control. Each row can be pre-charged and read out at different times, allowing different exposure durations for different rows. This segmentation enables the system to adapt to varying lighting conditions across the scene without requiring complex per-pixel control circuits, maintaining relative circuit simplicity while achieving high adaptability.
Solution Approach 2:
The patent implements dynamic exposure timing where the exposure duration and readout timing for different pixel rows can be varied independently. This dynamic control allows the system to adapt to different lighting conditions by adjusting which rows are pre-charged and when they are read out, providing versatility in handling varying illumination levels while maintaining a relatively simple circuit architecture based on standard CMOS technology.
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 enables high frame rate and high spatial resolution imaging without the need for multi-frame combinations or down-sampling, effectively addressing the limitations of traditional HDR imaging solutions.
Implementation Method 1
a photodiode coupled to accumulate image charge in response to incident light during an integration period
Data Source
AI summary
A pixel circuit includes a photodiode to accumulate image charge in response to incident light. A transfer transistor is disposed between the photodiode and a floating diffusion disposed in the first semiconductor layer to selectively transfer the image charge accumulated in the photodiode to the floating diffusion. A select circuit is disposed in second semiconductor layer coupled to a control terminal of the transfer transistor through a hybrid bond between the first and second semiconductor layers to select between first and second transfer control signals to control the transfer transistor. The select circuit is coupled to output the first transfer control signal in response to a precharge enable signal during a read out operation of a different row, and output the second transfer control signal in response to a sample enable signal during a read out operation of the row.