Dual Transfer Gate Pixel Structure for High Dynamic Range
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Solution Overview
Problem
Current pixel structures in image sensors have limitations in dynamic range, leading to distortion artifacts and increased noise, particularly due to the finite capacity of single charge conversion elements and uneven exposure periods across bright and dark areas.
Innovation Solution
A pixel structure with two transfer gates and two charge conversion elements, where the second element provides an overflow region and higher capacitance, allowing for increased dynamic range and lower noise readout, and enabling both rolling-shutter and global shutter operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single charge conversion element is used, then the pixel structure is simple, but the dynamic range is limited
Solution Approach 1:
The single charge conversion element is segmented into multiple charge conversion elements (first charge conversion element and second charge conversion element). Each element handles a portion of the dynamic range, with the first element capturing lower intensity values and the second element capturing higher intensity values, thereby extending the overall dynamic range of the pixel structure.
Solution Approach 2:
The patent introduces an additional dimension to the charge conversion system by adding multiple charge conversion elements with different capacitance values. This dimensional expansion allows the system to handle a broader range of light intensities by distributing charge storage across multiple elements with varying capacities.
2Measurement precision
If the first charge conversion element has small capacitance for low noise, then read noise is reduced, but the element saturates quickly limiting dynamic range
Solution Approach 1:
The charge conversion functionality is segmented across multiple elements with different capacitance values. The first charge conversion element uses small capacitance to achieve low read noise for dark areas, while the second charge conversion element uses large capacitance to handle bright areas, collectively providing both low noise performance and extended dynamic range.
Solution Approach 2:
Different charge conversion elements are assigned different local qualities (capacitance values) optimized for specific intensity ranges. The first element has small capacitance optimized for low-light conditions, while the second element has large capacitance optimized for bright-light conditions, allowing each element to excel in its designated operational range.
3Adaptability or versatility
If multiple charge conversion elements with different capacitances are used, then dynamic range is extended, but the device complexity increases
Solution Approach 1:
The pixel structure is segmented into distinct functional components (multiple transfer gates, multiple charge conversion elements) that can be independently controlled. This segmentation allows for manageable complexity while achieving extended dynamic range, as each segment can be optimized and controlled separately through the controller.
Solution Approach 2:
The multiple charge conversion elements serve universal functions of charge storage and conversion, but with different capacitance characteristics. This multi-functionality allows the system to handle various light intensity conditions using a standardized architectural pattern that can be extended to N elements if needed.
4Adaptability or versatility
If partial charge transfer through multiple transfers is used, then dynamic range is increased, but reading time increases
Solution Approach 1:
Charge is preliminarily distributed to multiple charge conversion elements during the exposure period through controlled transfer gate operations. This preliminary distribution allows the full dynamic range to be captured simultaneously during exposure, eliminating the need for sequential multiple readings and reducing total readout time.
Solution Approach 2:
The charge transfer to multiple charge conversion elements occurs continuously during the exposure period rather than requiring separate transfer steps after exposure. This continuous action ensures that the full dynamic range is captured in a single exposure cycle, maintaining high productivity without sacrificing dynamic range.
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 configuration enhances dynamic range, reduces noise, and allows for more complete charge transfer, improving image reconstruction and reducing image lag, while maintaining low read noise levels.
Implementation Method 1
a photo-sensitive element for generating charge in response to incident light
Data Source
AI summary
A pixel structure comprises a photo-sensitive element for generating charge in response to incident light. A first transfer gate is connected between the photo-sensitive element and a first charge conversion element. A second transfer gate is connected between the photo-sensitive element and a second charge conversion element. An output stage outputs a first value related to charge at the first charge conversion element and outputs a second value related to charge at the second charge conversion element. A controller controls operation of the pixel structures and causes a pixel structure. The controller causes the pixel structure to: acquire charges on the photo-sensitive element during an exposure period; transfer a first portion of the charges acquired during the exposure period from the photo-sensitive element to the first charge conversion element via the first transfer gate; and transfer a second portion of the charges acquired during the exposure period from the photo-sensitive element to the second charge conversion element via the second transfer gate.