4T Pixel Dynamic Range Extension via Charge Leakage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current high dynamic range image sensors, particularly 4T pixels, face limitations in dynamic range extension due to high fixed pattern noise, image lag, and complex pixel circuitry, which are not suitable for high-resolution applications like automotive driving assistance systems.
Innovation Solution
A method that involves a 4T pixel with a pinned photodiode and floating diffusion node, where charge leakage from the photodiode potential well to the floating diffusion node allows for non-linear signal processing, combining linear and non-linear signals to reduce noise and extend dynamic range while maintaining low fixed pattern noise across the entire range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple frame recombination approaches are used to extend dynamic range, then dynamic range is improved, but image lag increases and processing complexity increases
Solution Approach 1:
The pixel circuit is segmented into multiple functional blocks: photodiode for linear signal capture, floating diffusion for non-linear signal capture, and separate readout paths for each signal type. This segmentation allows simultaneous acquisition of both linear and non-linear signals without requiring temporal separation or frame recombination, eliminating image lag while maintaining extended dynamic range.
2Adaptability or versatility
If multiple frame recombination approaches are used to extend dynamic range, then dynamic range is improved, but device complexity increases
Solution Approach 1:
The patent merges the linear and non-linear signal capture functions into a single pixel circuit that operates simultaneously. The photodiode and floating diffusion share the same pixel structure and readout timing, eliminating the need for separate frame buffers and processing units required by multiple frame recombination approaches. This integration reduces processing complexity while achieving extended dynamic range.
3Adaptability or versatility
If autoreset and multiple integration potential well pixels are used to extend dynamic range, then dynamic range is improved, but pixel circuitry complexity increases
Solution Approach 1:
The pixel circuit is designed as a universal structure where the photodiode and floating diffusion serve multiple functions: the photodiode captures linear signals while the floating diffusion captures non-linear signals, and both signals are read out through the same transistor network. This multi-functionality eliminates the need for separate circuitry for each signal type, reducing pixel circuitry complexity while maintaining extended dynamic range capability.
4Adaptability or versatility
If logarithmic response pixel with n+−p substrate diode is used to extend dynamic range, then dynamic range is improved, but dark signal performance deteriorates and fixed pattern noise increases
Solution Approach 1:
The patent applies local quality by using different semiconductor structures in different regions: a pinned photodiode with n+−p substrate for linear signal capture and a floating diffusion with p+−n substrate for non-linear signal capture. Each region is optimized for its specific function, with the pinned photodiode providing low dark noise for linear signals and the floating diffusion providing non-linear response for high dynamic range extension, thereby maintaining dark signal performance while achieving extended 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 approach effectively reduces noise and extends the dynamic range of image sensors, preserving low light performance and reducing fixed pattern noise, making it suitable for high dynamic range scenes without the need for complex pixel circuitry or high computational power.
Implementation Method 1
a pinned photodiode and a floating diffusion node, where charge leakage from the photodiode potential well to the floating diffusion node allows for non-linear signal processing
Implementation Method 2
said photodiode potential well and said potential well of said floating diffusion node being separated by a transfer gate potential barrier
Data Source
AI summary
A method for noise reduction in an imaging device comprises a 4T pixel in operation, whereby the 4T pixel comprises a pinned photodiode and a floating diffusion node. The method includes the steps of: detecting a signal impinging on the 4T pixel of the imaging device and integrating the charge of the detected signal simultaneously in the photodiode potential well and the potential well of the floating diffusion node; deriving a linear signal proportional to the detected signal from the charge in the photodiode potential well; deriving a compressed signal from the charge in the potential well of the floating diffusion node, while keeping the compressed signal separate from the linear signal, and the compressed signal being a non-linear function of the detected signal; and summing the linear signal and a linearized version of the compressed signal and performing a non-linear conversion on the summation signal to fit the imaging device's output range.