Boosted Floating Diffusion Pixel Circuit for Wider Dynamic Range
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Solution Overview
Problem
Current image sensors face challenges in achieving improved image quality due to limitations in signal transmission efficiency and dynamic range, particularly in varying illuminance conditions.
Innovation Solution
The proposed image sensor design incorporates a photodiode, transmission transistors, switching transistors, capacitors, and a boosting signal mechanism to enhance signal transmission efficiency and dynamic range by using a boosting signal to increase the potential of the floating diffusion region, allowing for more efficient charge transfer and improved image sensing across different illuminance levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional image sensor design is used, then device complexity is low, but image quality and dynamic range are limited
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks including photodiode, transmission transistor, switching transistor, and multiple capacitors (first capacitor, second capacitor, third capacitor) with distinct functions. This segmentation allows each component to be optimized independently for its specific role in signal processing, thereby improving overall image quality while managing complexity through modular design
Solution Approach 2:
The patent implements a nested capacitor structure where the second capacitor is formed between the first capacitor and the third capacitor. The second capacitor includes a first electrode overlapping the first capacitor and a second electrode overlapping the third capacitor, creating a nested arrangement that maximizes capacitance within limited pixel area, thus improving dynamic range without proportionally increasing device footprint
2Measurement precision
If signal processing is enhanced to improve image quality, then signal-to-noise ratio increases, but device complexity increases
Solution Approach 1:
The patent implements preliminary charge transfer from the photodiode to the first capacitor through the transmission transistor before any switching or signal processing operations. This preliminary action ensures that signal charges are immediately captured and isolated, preventing noise accumulation and enabling subsequent processing steps to operate on already-separated signal components, thereby improving signal-to-noise ratio
Solution Approach 2:
The patent introduces multiple intermediary capacitors (first, second, and third capacitors) that serve as intermediate storage and transfer elements between the photodiode and final signal output. These intermediary capacitors enable staged charge transfer and signal processing, allowing noise filtering and signal enhancement to occur progressively through each stage rather than requiring a single complex processing step
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 image sensing quality by increasing transmission efficiency and dynamic range, enabling better performance in both low and high illuminance environments, thereby improving the overall image quality and full-well capacity of the image sensor.
Implementation Method 1
Each of the pixels may include a photodiode. The photodiode may serve to convert incident light into an electrical signal.
Data Source
AI summary
An image sensor is provided. The image sensor comprises a photodiode, a transmission transistor having a first end connected to the photodiode and a second end connected to a first node, a first switching transistor having a first end connected to the first node, a first capacitor having a first electrode connected to a second end of the first switching transistor, a second capacitor having a first electrode connected to the first node. A second electrode of the first capacitor is configured to receive a power voltage, and a second electrode of the second capacitor is configured to receive a boosting signal.