Imaging Pixel Floating Diffusion Segmentation for Sensitivity
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Solution Overview
Problem
In image sensors, there is a trade-off between charge-voltage conversion sensitivity and saturated charge number, where reducing the floating diffusion capacity to improve sensitivity results in increased voltage changes, making it difficult to handle charges beyond allowable voltage values, and existing methods require high reset voltages that are challenging to realize, especially in mounting and pixel sharing scenarios.
Innovation Solution
The imaging device incorporates a pixel configuration with a photoelectric conversion element, transfer elements, a reset element, a floating diffusion, and an amplification element, where the transfer elements and reset element are transistors, and the floating diffusion is coupled between the second transfer element and the amplification element, allowing for improved charge transfer and voltage amplification, enabling better sensitivity without the need for high reset voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the floating diffusion capacity is reduced to improve charge-voltage conversion sensitivity, then the sensitivity is improved, but the voltage change of the battery is increased and charges exceeding allowable voltage values cannot be read
Solution Approach 1:
The pixel is divided into multiple regions with different floating diffusion capacities. A first region has a first floating diffusion capacity optimized for high sensitivity, while a second region has a second floating diffusion capacity optimized for handling larger charge values. This segmentation allows the sensor to simultaneously achieve high sensitivity for low-light conditions and proper handling of bright conditions without requiring a single floating diffusion to compromise between both requirements.
2Measurement precision
If the charge reset switch is removed to increase sensitivity, then the sensitivity is increased, but a very high reset voltage is required which is difficult to realize in mounting
Solution Approach 1:
The invention removes the charge reset switch from the pixel circuit to eliminate the need for high reset voltages. Instead of using a reset switch that requires high voltage to clear charges, the design relies on the natural discharge characteristics of the floating diffusion regions and the transfer mechanism to reset charges, thereby achieving high sensitivity without the manufacturing complexity and high voltage requirements of traditional reset switches.
Solution Approach 2:
The invention introduces a transfer element as an intermediary between the photoelectric conversion element and the floating diffusion. This transfer element mediates the charge transfer process, allowing charges to be moved to the floating diffusion region without requiring a high-voltage reset switch. The transfer element enables controlled charge transfer at lower voltages while maintaining the ability to clear charges when needed.
3Device complexity
If a single floating diffusion is used per pixel, then the pixel structure is simple, but the dynamic range is limited and cannot handle both low-light and high-light conditions optimally
Solution Approach 1:
The pixel is divided into multiple regions with different floating diffusion capacities. A first region has a first floating diffusion capacity optimized for high sensitivity, while a second region has a second floating diffusion capacity optimized for handling larger charge values. This segmentation allows the sensor to simultaneously achieve high sensitivity for low-light conditions and proper handling of bright conditions without requiring a single floating diffusion to compromise between both requirements.
Solution Approach 2:
Each pixel is equipped with multiple floating diffusion regions that can handle different ranges of charge values. This multi-functionality allows the same pixel structure to optimally process both low-light signals (using the high-sensitivity floating diffusion) and high-light signals (using the high-capacity floating diffusion), thereby expanding the dynamic range without requiring different pixel types for different lighting conditions.
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 charge-voltage conversion sensitivity while allowing for the handling of a wider range of charge values, improving image quality and dynamic range without the limitations of high reset voltage requirements.
Implementation Method 1
a photoelectric conversion element to convert incident light into electric charge
Data Source
AI summary
An imaging device comprises a first pixel. The first pixel includes a photoelectric conversion element to convert incident light into electric charge, and a first transfer element and a second transfer element to transfer the electric charge. The first transfer element is coupled between the photoelectric conversion element and the second transfer element. The first pixel includes a reset element coupled to the second transfer element, a floating diffusion, and an amplification element coupled to the floating diffusion to amplify a voltage of the floating diffusion. The floating diffusion is coupled between the second transfer element the amplification element.