Dual-Photodiode Pixel Circuit for Wide Dynamic Range Imaging
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Solution Overview
Problem
Current image sensors face challenges in achieving improved image quality due to limitations in pixel design and signal processing, particularly in handling varying illuminance levels, which affects the dynamic range and signal-to-noise ratio.
Innovation Solution
The design incorporates a unit pixel with a dual photoelectric converter system, including a large and small photodiode, along with transfer transistors and capacitors, allowing for multiple signal operations and dynamic range adjustments through switch control, enhancing full well capacity and signal processing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional single photodiode design is used, then the device complexity is low, but the dynamic range and image quality are limited
Solution Approach 1:
The pixel is divided into multiple photodiodes (first photodiode, second photodiode, third photodiode) with different areas, each optimized for specific illuminance conditions. This segmentation allows simultaneous capture of signals across a wide dynamic range while maintaining manageable complexity through modular architecture
Solution Approach 2:
The patent implements dynamic capacitance adjustment by controlling switches (first switch, second switch, third switch) to connect different capacitors (first capacitor, second capacitor, third capacitor) based on illuminance levels. This dynamic reconfiguration optimizes the full well capacity for different lighting conditions, improving image quality without permanent structural complexity
2Adaptability or versatility
If the full well capacity is increased to handle high illuminance, then the dynamic range improves, but the signal-to-noise ratio in low illuminance conditions deteriorates
Solution Approach 1:
Different photodiodes are designed with different areas optimized for specific functions: larger photodiodes for high illuminance capture, smaller photodiodes for low illuminance sensitivity. Each photodiode-capacitor combination provides locally optimized quality for its intended illuminance range, achieving both high dynamic range and maintained signal-to-noise ratio
Solution Approach 2:
The system changes the effective capacitance value dynamically by switching between different capacitor configurations based on illuminance detection. This parameter adjustment allows the full well capacity to be optimized for each lighting condition, preventing signal saturation in bright light while maintaining adequate capacity for low-light signals
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 improves image quality by increasing the dynamic range and signal-to-noise ratio, enabling effective image sensing in both low and high illuminance environments, and reduces noise through correlated double sampling.
Implementation Method 1
Each of the pixels may include, for example, a photodiode (PD). The photodiode may serve to convert incident light thereto into an electrical signal.
Data Source
AI summary
An image sensor with improved image quality is provided. An image sensor includes a pixel array including a plurality of unit pixels. Each of the unit pixels includes a first photoelectric converter configured to convert received light into charges, a first transfer transistor electrically connected between the first photoelectric converter and a first node, a connection transistor disposed connected to a second node and the first node, a dual conversion transistor electrically connected between a third node and the second node, a second transfer transistor electrically connected between a fourth node and the third node, a second photoelectric converter electrically connected to the fourth node and configured to convert the received light into charges, a first switch electrically connected to the second photoelectric converter and the fourth node, a first capacitor electrically connected to the fourth node, and a electrically second capacitor connected to the third node.