Imaging Pixel Charge Storage Regions for Global Shutter Noise Reduction
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Solution Overview
Problem
Conventional CMOS image sensors with global shutter functionality suffer from increased noise and decreased image quality due to incident light affecting charge levels in the charge storage region, which is not converted by the photodiode.
Innovation Solution
Incorporating a second charge storage region that is not coupled to the photodiode, allowing for the isolation and measurement of noise from incident light, and using a correlated double sampling technique to subtract noise from the total charge, thereby improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a charge storage region is incorporated into each pixel to store charge from the photodiode until read out, then global shutter functionality is achieved, but incident light affecting charge levels in the charge storage region increases noise and decreases image quality
Solution Approach 1:
The pixel is segmented into multiple charge storage regions: a first charge storage region coupled to the photodiode for storing signal charge, and a second charge storage region not coupled to the photodiode for storing only noise charge from incident light. This segmentation allows independent measurement and subtraction of noise, resolving the contradiction between maintaining global shutter functionality and reducing noise.
Solution Approach 2:
The noise component is extracted by isolating a second charge storage region that receives only incident light without signal charge from the photodiode. By taking out the noise measurement separately, the patent enables noise subtraction from the total charge, thereby improving image quality while preserving global shutter operation.
2Device complexity
If a single charge storage region is used, then device complexity is reduced, but the ability to isolate and measure noise from incident light is lost
Solution Approach 1:
The charge storage function is segmented into two separate regions with distinct coupling configurations: one region receives charge from the photodiode (signal + noise), while the other receives only incident light (noise only). This segmentation enables precise noise measurement despite increased structural complexity, as each region serves a specific measurement purpose.
Solution Approach 2:
The noise measurement capability is extracted by creating a dedicated second charge storage region that is decoupled from the photodiode. This extraction allows independent noise characterization without interfering with the primary signal charge storage function, achieving precise noise measurement at the cost of additional structural elements.
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 reduces noise in the image sensor by accurately isolating and accounting for charge from incident light, resulting in enhanced image quality and reduced noise levels.
Implementation Method 1
Each pixel typically includes a photosensor such as a photodiode that receives incident photons (light) and converts the photons into electrical signals
Data Source
AI summary
An imaging pixel may be provided with a photodiode and a floating diffusion region. The pixel may include multiple charge storage regions interposed between the photodiode and the floating diffusion region. A first charge storage region may be used to store charge from the photodiode for global shutter functionality. A second charge storage region may not be coupled to the photodiode. The second charge storage region may be used to determine how much charge is generated in the charge storage region from incident light on the charge storage region. The second charge storage region may help account for incident light noise in the first charge storage region. The second charge storage region may be the same size as the first charge storage region, or may be smaller than the first charge storage region.