In-Pixel High Dynamic Range Imaging via MOS Capacitance Coupling
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Solution Overview
Problem
Existing image capture devices face challenges in achieving high dynamic range imaging (HDR) due to the limitations of pixel cell size, which results in reduced signal strength and signal-to-noise ratio (SNR), especially under varying lighting conditions.
Innovation Solution
The solution involves coupling a floating diffusion node of the imaging pixel to a plurality of metal-oxide semiconductor (MOS) capacitance regions, each with different threshold voltages, allowing the capacitance to vary with illumination conditions, thereby increasing the dynamic range and SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the pixel cell size is decreased, then the resolution is improved, but the signal strength and dynamic range are reduced
Solution Approach 1:
The pixel cell is segmented into multiple photodiodes (first photodiode and second photodiode) that can independently capture light signals. This segmentation allows each photodiode to be optimized for specific functions while maintaining overall signal strength despite smaller pixel dimensions.
Solution Approach 2:
The patent introduces a temporal dimension by implementing dual gain modes that switch between different signal processing paths. The first photodiode connects to first readout circuitry for one gain mode, while the second photodiode connects to second readout circuitry for another gain mode, adding a time-based dimension to signal capture that expands dynamic range without increasing physical pixel area.
2Measurement precision
If the floating diffusion node size is decreased to achieve high conversion gain, then the signal-to-noise ratio is improved, but the dynamic range is reduced due to saturation
Solution Approach 1:
The patent implements dynamic switching between dual gain modes where the pixel can adapt its operating characteristics based on illumination conditions. The floating diffusion node dynamically connects to different readout circuitry paths (first or second readout circuitry) depending on the light intensity, allowing the system to maintain high signal-to-noise ratio in low light while avoiding saturation in bright light conditions.
Solution Approach 2:
The patent changes the electrical parameters of the pixel by switching between different gain modes. The first readout circuitry operates with one gain setting optimized for low-light conditions, while the second readout circuitry operates with a different gain setting optimized for bright-light conditions. This parameter switching allows the same physical pixel structure to achieve both high signal-to-noise ratio and wide dynamic range.
3Measurement precision
If the pixel cell is designed for high conversion gain, then the signal-to-noise ratio is improved, but the capacity to handle high illumination conditions is reduced
Solution Approach 1:
The pixel is segmented into two photodiodes with different functional optimizations. The first photodiode is optimized for high conversion gain and connects to first readout circuitry for low-light conditions, while the second photodiode handles bright-light conditions by connecting to second readout circuitry. This segmentation allows each component to be specialized for its optimal operating range.
Solution Approach 2:
The pixel implements dynamic routing where the photodiodes can switch connections between different readout circuitry paths based on illumination intensity. Under bright light conditions, the system dynamically routes signals through the second readout circuitry which has higher capacity, while under low light conditions, it uses the first readout circuitry optimized for high gain, thus adapting to varying illumination levels.
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 signal-to-noise ratio of the imaging system, enabling effective HDR performance across a wide range of lighting conditions.
Implementation Method 1
photodiode 101 and floating diffusion node 106 are reset by temporarily asserting the reset signal RST and transfer signal TX. The accumulating window (i.e., exposure period) is commenced by de-asserting the transfer signal TX and permitting incident light to charge photodiode 101. As photo-generated electrons accumulate on photodiode 101, its voltage decreases
Implementation Method 2
coupling a floating diffusion node of the imaging pixel to a plurality of metal-oxide semiconductor (MOS) capacitance regions. Each of the plurality of MOS capacitance regions may have different threshold voltage values
Data Source
AI summary
Embodiments of the invention describe providing high dynamic range imaging (HDRI or simply HDR) to an imaging pixel by coupling a floating diffusion node of the imaging pixel to a plurality of metal-oxide semiconductor (MOS) capacitance regions. It is understood that a MOS capacitance region only turns “on” (i.e., changes the overall capacitance of the floating diffusion node) when the voltage at the floating diffusion node (or a voltage difference between a gate node and the floating diffusion node) is greater than its threshold voltage; before the MOS capacitance region is “on” it does not contribute to the overall capacitance or conversion gain of the floating diffusion node.Each of the MOS capacitance regions will have different threshold voltages, thereby turning “on” at different illumination conditions. This increases the dynamic range of the imaging pixel, thereby providing HDR for the host imaging system.