Optically Black Reference Pixel Integration Control in CMOS iSoC
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Solution Overview
Problem
Conventional CMOS imaging Sensors-on-Chip (iSoC) suffer from undesirable artifacts like rolling shutter skew and partial exposure due to readout architectures, and are prone to fixed pattern noise (FPN) which degrades image quality, especially in low-light conditions.
Innovation Solution
The implementation of a system and method that utilizes vertical pointers to manage the integration time of optically black reference pixels independently, mitigating column FPN and preventing blooming by using all available optically black pixel statistics, and providing a means to shorten the integration time of these pixels relative to active pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the integration time of optically black reference pixels is the same as active pixels, then all pixels are exposed uniformly, but fixed pattern noise accumulates and degrades image quality
Solution Approach 1:
The patent divides the pixel array into two distinct groups: optically black reference pixels and active imaging pixels. Each group is assigned independent integration time control through separate reset mechanisms (first reset component for reference pixels, second reset component for active pixels). This segmentation allows the reference pixels to have their integration time independently managed to minimize FPN while active pixels maintain full integration for imaging, resolving the contradiction between uniform exposure and FPN accuracy.
2Measurement precision
If the integration time of optically black reference pixels is shortened, then FPN is minimized and measurement accuracy improves, but dark current accumulation increases
Solution Approach 1:
The patent implements periodic resetting of optically black reference pixels through a dedicated first reset component that operates independently from the active pixel reset cycle. This periodic action allows reference pixels to be reset at specific intervals during the frame period, minimizing their integration time and thereby reducing dark current accumulation while maintaining accurate FPN measurements. The periodic reset ensures reference pixels do not accumulate excessive dark current even when integration time is shortened.
3Device complexity
If a single readout architecture is used for all pixels, then device complexity is reduced, but rolling shutter skew and partial exposure artifacts occur
Solution Approach 1:
The patent segments the readout architecture into two independent pathways: one for optically black reference pixels and another for active imaging pixels. The read component includes separate control logic that can independently manage the readout timing and sequence for each pixel type. This segmentation eliminates rolling shutter skew and partial exposure artifacts by ensuring reference pixels are read at the appropriate times without interfering with active pixel readout, while maintaining manageable device complexity through systematic organization of the dual pathways.
4Measurement precision
If all optically black pixel statistics are used for FPN correction, then measurement precision improves, but blooming occurs from surrounding active pixels
Solution Approach 1:
The patent applies preliminary action by resetting optically black reference pixels before active imaging pixels during the frame period. This preliminary reset ensures that when reference pixels are exposed, surrounding active pixels have already been reset and cannot bloom into the reference pixels. This timing sequence allows all optically black pixel statistics to be safely used for FPN correction without contamination from blooming, thereby improving measurement precision while preventing the harmful blooming effect.
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 improves the quality of optically black reference pixels by minimizing pixel FPN, reducing dark current accumulation, and enhancing the accuracy of FPN offset determination, leading to better image quality and reduced noise in CMOS iSoC systems.
Implementation Method 1
each pixel cell in the array can include a photodetector (e.g., photogate, photoconductor, photodiode, and so on) that overlays a substrate for yielding a photo-generated charge
Data Source
AI summary
Aspects relate to improved optically black reference pixels in a CMOS iSoc sensor. A system can include a pointer P1 that indicates pixels to be read out during a readout time interval, a pointer P2 that indicates pixels to be reset during the time interval, and a pointer P3 that preserves a validity of a frame. The system also includes a pointer P4 configured to mitigate an integration time of column fixed pattern noise (FPN) rows independently of the integration time of other rows. In some aspects, pointer P4 can mitigate blooming into sampled rows from surrounding rows. Pointer P4 can be continuously rotated, in an aspect. Further, in some aspects, pointer P4 can jump on a second cycle to arrive one line before pointer P1.