CMOS Image Sensor Pixel Structure for HDR SN Improvement
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Solution Overview
Problem
Existing solid-state imaging devices face challenges in achieving a good signal-to-noise (SN) characteristic at the connection point, particularly due to limitations in handling charges accumulated in capacitance, which affects dark current and fixed pattern noise removal.
Innovation Solution
The implementation of a solid-state imaging device with a pixel array unit comprising multiple unit pixels, including a small pixel with a first photoelectric conversion unit and a large pixel with a second photoelectric conversion unit divided into multiple regions, where the large pixel has a stronger electric field and improved transfer capability, allowing for increased saturation signal and better noise handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If charges are accumulated directly in floating diffusion (FD) in the small pixel, then the pixel can handle charges using double data sampling (DDS), but correlated double sampling (CDS) method cannot be adopted, resulting in inability to remove dark current and fixed pattern noise (FPN), which deteriorates the SN characteristic at the connection point
Solution Approach 1:
The patent introduces a transfer gate as an intermediary component between the photodiode and the floating diffusion. This transfer gate enables controlled charge transfer, allowing the system to accumulate charges in the photodiode and then transfer them to the floating diffusion in a controlled manner, thereby enabling CDS method to be applied and dark current and FPN to be removed while maintaining charge handling capability
Solution Approach 2:
The patent divides the pixel structure into distinct functional regions: a photodiode for charge accumulation, a transfer gate for controlled charge transfer, and a floating diffusion for signal processing. This segmentation allows each component to perform its specific function optimally, enabling both charge handling and noise removal capabilities
2Adaptability or versatility
If a large pixel and a small pixel having different sensitivities are provided for a unit pixel to perform high dynamic range technology, then the dynamic range is expanded, but it has been difficult to obtain a good signal to noise (SN) characteristic at the connection point where two signals are used to calculate the pixel value
Solution Approach 1:
The patent applies different structural configurations to different pixels within the same unit pixel: the large pixel includes a photodiode with a transfer gate and floating diffusion structure that enables CDS method, while the small pixel has a different configuration. This local differentiation allows each pixel type to be optimized for its specific function while maintaining overall system performance
Solution Approach 2:
The patent changes the structural parameters of the large pixel by introducing a transfer gate and floating diffusion, which fundamentally changes the charge handling capability and enables CDS method. This parameter change allows the large pixel to achieve both high sensitivity and good SN characteristic at the connection point
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 the SN characteristic by increasing the saturation signal amount of the large pixel, thereby improving the SN ratio at the connection point and reducing noise influence at higher illuminance levels.
Implementation Method 1
a small pixel having a first photoelectric conversion unit and a first on-chip lens configured to allow light to enter the first photoelectric conversion unit; and a large pixel having a second photoelectric conversion unit
Data Source
AI summary
The present technology relates to a solid-state imaging device and an electronic device enabling improvement of an SN characteristic. A solid-state imaging device includes a pixel array unit provided with multiple unit pixels. Each of the unit pixels includes: a small pixel having a first photoelectric conversion unit and a first on-chip lens configured to allow light to enter the first photoelectric conversion unit; and a large pixel having a second photoelectric conversion unit divided into multiple regions, and a second on-chip lens that can condense more light than the first on-chip lens and allows light to enter the second photoelectric conversion unit. The present technology may be applied to a CMOS image sensor.