Imaging Pixel Circuit Reset Noise Suppression Feedback
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Solution Overview
Problem
Current imaging devices face challenges in effectively reducing reset noise, particularly in CMOS solid-state imaging devices, where the correlation between reset noise in signal and reset voltages makes it difficult to eliminate random noise, especially with decreasing pixel sizes and increased unit pixel counts.
Innovation Solution
The proposed imaging device incorporates a pixel structure with a photoelectric converter, a signal detection circuit featuring a first transistor for amplification and a second transistor for output transmission, along with a feedback circuit that forms a feedback loop not passing through the first transistor, and includes a voltage supply circuit providing multiple voltages to the second transistor, allowing for effective suppression of reset noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is decreased to increase unit pixel count, then productivity and resolution are improved, but reset noise increases and becomes difficult to suppress
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: photoelectric converter, first transistor for signal amplification, second transistor for output, and feedback circuit. This segmentation allows each component to be optimized independently for noise suppression while maintaining overall pixel functionality.
Solution Approach 2:
A feedback circuit is implemented that feeds back the output signal to the input node (photoelectric converter or floating diffusion). This negative feedback mechanism suppresses reset noise by canceling out noise components through the feedback path, enabling effective noise reduction even in smaller pixels.
2Ease of manufacture
If conventional CDS method is used, then manufacturing simplicity is maintained, but reset noise cannot be effectively reduced
Solution Approach 1:
The patent implements a feedback circuit within the pixel that actively suppresses reset noise through negative feedback. This approach achieves superior noise reduction compared to conventional CDS while remaining compatible with standard CMOS manufacturing processes, as the feedback circuit uses conventional transistors and capacitors.
Solution Approach 2:
The feedback circuit is designed to counteract reset noise before it propagates through the signal path. By applying preliminary anti-action through the feedback mechanism, the noise is suppressed at its source rather than attempting to remove it later in the signal processing chain.
3Productivity
If pixel area is reduced, then productivity increases, but thermal noise management becomes more difficult
Solution Approach 1:
The circuit is segmented into distinct functional blocks with dedicated noise suppression mechanisms. The feedback circuit specifically targets thermal noise generated in the photoelectric converter and transistors, allowing effective thermal noise management even in reduced-area pixels.
Solution Approach 2:
The feedback mechanism suppresses thermal noise by detecting noise components at the output and counteracting them at the input. This continuous noise cancellation enables maintainment of signal quality despite the reduced pixel area that would otherwise increase thermal noise density.
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 enables significant reduction of reset noise while maintaining high-speed noise suppression and stable operation, even with smaller pixel areas, by utilizing a feedback loop and multiple voltage supplies to manage and minimize thermal noise.
Implementation Method 1
a photoelectric converter that generates an electric signal through photoelectric conversion of incident light
Data Source
AI summary
An imaging device having a pixel including: a photoelectric converter that generates an electric signal through photoelectric conversion of incident light; a first transistor that has a gate coupled to the photoelectric converter and that amplifies the electric signal; and a second transistor that has a gate coupled to the photoelectric converter, one of a source and a drain of the second transistor being coupled to the photoelectric converter. The imaging device further includes a voltage supply circuit configured to supply two or more different voltages to the other of the source and the drain of the second transistor.