Pixel Array Image Sensor Noise Reduction via Vertical Electrode
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Solution Overview
Problem
Current image sensors face challenges in enhancing reliability, particularly in capturing light beyond the visible spectrum, and in effectively removing noise from image signals.
Innovation Solution
The development of a pixel array and image sensor design that includes a photoelectric element generating charge from light, a pixel circuit with a floating diffusion, a vertical pixel electrode, an analog-to-digital converter, and a memory element, which enables the generation and storage of digital signal values, and incorporates a reset transistor and driver transistor for noise reduction through correlated double sampling and true correlated double sampling operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel structure is used, then the device complexity is low, but the reliability and noise reduction capability are insufficient
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: photoelectric element for charge generation, floating diffusion for charge storage, ADC for analog-to-digital conversion, and memory element for data storage. This segmentation allows each component to be optimized independently for reliability while maintaining manageable complexity through modular design.
Solution Approach 2:
A vertical pixel electrode is introduced as an intermediary component connecting the photoelectric element to the floating diffusion. This intermediary structure improves charge transfer efficiency and reliability while isolating the photoelectric element from direct lateral connections, reducing noise interference.
2Measurement precision
If noise reduction through correlated double sampling is implemented, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The memory element stores the digital reset value before the actual image signal is processed. This preliminary storage enables subsequent subtraction of the reset value from the signal value to remove noise, achieving correlated double sampling without requiring complex additional circuitry during the measurement phase.
Solution Approach 2:
The reset operation and signal reading operation are merged into a unified pixel circuit structure. Both operations use the same floating diffusion, ADC, and memory element, achieving noise reduction through differential measurement while avoiding the need for separate dedicated circuits for each function.
3Object-generated harmful factors
If multiple transistors and circuit elements are added for noise reduction, then the object-generated harmful factors decrease, but the manufacturing precision requirements increase
Solution Approach 1:
The floating diffusion serves multiple functions: it acts as a charge storage node from the photoelectric element, a reset target for noise reduction, and an input to the ADC for signal conversion. This multi-functionality reduces the need for separate dedicated structures, lowering manufacturing precision requirements while achieving noise reduction.
Solution Approach 2:
The circuit operates by changing the electric potential parameter of the floating diffusion between reset state and signal state. This parameter-based operation allows noise reduction through voltage-level differentiation rather than requiring physically distinct structures, reducing manufacturing complexity and precision requirements.
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 design enhances the reliability and noise reduction capabilities of image sensors, improving their ability to capture light across various wavelength bands and providing improved image quality by effectively removing noise from signal potentials.
Implementation Method 1
a photoelectric element formed on a substrate and that generates charge from light
Data Source
AI summary
A pixel array includes a plurality of pixels. Each of the pixels includes a photoelectric element formed on a substrate and that generates charge from light, and a pixel circuit formed between the photoelectric element and the substrate and that outputs a digital signal value based on an amount of the generated charge. The pixel circuit includes a floating diffusion formed in the substrate and that stores the charge therein, a vertical pixel electrode that connects the floating diffusion to the photoelectric element and extends in a direction perpendicular to the substrate, an analog-to-digital converter that converts an electric potential of the floating diffusion into the digital signal value, and a memory element that stores the digital signal value.