Front-end Pixel Fixed Pattern Noise Correction in Wide Dynamic Range Imaging Arrays
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Solution Overview
Problem
Conventional CMOS imaging devices suffer from pixel fixed-pattern noise (FPN) due to mismatches in pixel characteristics, which are not effectively addressed by existing feedback-based systems, especially in four transistor (4T) and five transistor (5T) pixels, limiting image quality and dynamic range.
Innovation Solution
A discrete time and feed-forward correction system that includes a reset component, an analyzer component to sample the reset level, and an adjustment component to adjust the reset bus, facilitating the correction of fixed pattern noise, while also enabling external readout and using a switched capacitor block for power supply adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If feedback-based systems are used to correct fixed pattern noise, then some noise correction can be achieved, but the correction is not effective enough and device complexity increases
Solution Approach 1:
The patent applies preliminary action by performing reset level sampling and correction calculation before the actual image capture process. The analyzer component samples the reset level of each pixel, and the adjustment component calculates correction values in advance, so that when the pixel is read out, the FPN correction is already prepared and applied, improving correction effectiveness without adding complex real-time feedback loops
Solution Approach 2:
The patent extracts the FPN correction function from the pixel circuit itself and places it in the column circuitry. By using a shared correction resource in the column circuit, each pixel's FPN is corrected using correction values stored in memory, rather than requiring complex feedback mechanisms at the pixel level, thus reducing overall device complexity while maintaining correction effectiveness
2Ease of manufacture
If four transistor (4T) and five transistor (5T) pixels are used, then device complexity is reduced and manufacturing is easier, but fixed pattern noise is not effectively addressed
Solution Approach 1:
The patent introduces an intermediary correction mechanism in the column circuitry that works with the simple 4T/5T pixel structures. The analyzer component and adjustment component act as intermediaries that sample reset levels and apply correction values to the readout signal, enabling FPN correction without requiring complex pixel-level circuitry or additional transistors in the pixel itself
Solution Approach 2:
The patent implements feedback by sampling the reset level of each pixel and using that information to calculate correction values. The adjustment component uses the sampled reset level to determine how much correction is needed, creating a feedback loop that adapts to each pixel's specific FPN characteristics while working with the simple 4T/5T pixel architecture
3Reliability
If global shutter is implemented, then motion artifacts are avoided, but overhead in device design and operation increases
Solution Approach 1:
The patent segments the correction process into separate functional components: a reset component that resets the pixel, an analyzer component that samples the reset level, and an adjustment component that applies correction. This segmentation allows the FPN correction to be handled independently from the imaging process, enabling global shutter operation without adding significant overhead to the pixel circuit or readout mechanism
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 system effectively corrects FPN, enhances image quality, and maintains Correlated Double Sampling (CDS) functionality, providing a wide dynamic range and efficient global shutter operation with reduced temporal noise.
Implementation Method 1
a reset component configured to reset a pixel of the pixel array
Implementation Method 2
an analyzer component configured to sample a reset level of the pixel
Implementation Method 3
an adjustment component configured to adjust a reset bus in response to the sampled reset level, wherein the adjustment to the reset bus facilitates correction of the fixed pattern noise
Implementation Method 4
a detection component configured to sample a signal level of the pixel for external readout from the pixel array
Data Source
AI summary
Aspects describe front-end pixel fixed pattern noise correction in imaging arrays having wide dynamic range. A photosensor of a first pixel in a first row of an array is reset and a first reset level of the first pixel is measured. The array comprises a plurality of pixels arranged in rows and columns. In response to a result of the first reset level, a reset bus is altered. A feed-forward adjustment of the photosensor of the first pixel is performed to substantially remove fixed-pattern noise. An external readout from the photosensor can occur with substantially all the fixed-pattern noise removed. In some aspects, the adjustment is performed by a switched capacitor block.