Two-Line TDI Linear Image Sensor with Shared Charge Storage Node
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing linear image sensors face challenges in achieving sufficient image signal amplitude and signal-to-noise ratio when the relative movement between the object and sensor is fast, particularly with MOS technology, which is complicated by the need for multiple lines of pixels and synchronization issues.
Innovation Solution
A linear image sensor using only two lines of pixels operating in TDI mode, where each pixel includes a photodiode and a shared charge storage node with a transfer gate, allowing charge transfer between the photodiodes and storage node, enabling improved sensitivity and signal-to-noise ratio without complex pixel technology modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the integration time is extended to gather more photons, then the sensitivity is improved, but the image resolution in the movement direction deteriorates
Solution Approach 1:
The sensor is divided into two distinct lines of pixels that operate in sequence. Each line captures the same image line at different time points, allowing the signal to be integrated over time while maintaining spatial resolution. The segmentation of the pixel array into multiple operational lines enables TDI mode without requiring complex multi-line structures.
Solution Approach 2:
The first line of pixels performs preliminary charge accumulation during the exposure period. The charge is then transferred to a storage node before the second line captures the same scene. This preliminary action allows sequential integration of signals from multiple lines, improving sensitivity while maintaining the ability to resolve fast-moving objects through synchronized charge transfer.
2Illumination intensity
If multiple lines of pixels are used to improve sensitivity and signal-to-noise ratio, then the sensitivity is improved, but the device complexity increases
Solution Approach 1:
The patent merges the functionality of multiple pixel lines by sharing a common storage node between the first and second lines. This consolidation reduces the overall complexity compared to fully independent multi-line structures, as the storage node serves dual purposes for both lines while still enabling sequential charge accumulation and signal integration.
Solution Approach 2:
The storage node is designed to serve multiple functions: it stores charge from the first line, receives charge from the second line, and enables readout for both lines. This multi-functional design reduces the total component count and simplifies the pixel structure while maintaining the sensitivity benefits of multi-line TDI operation.
3Ease of manufacture
If MOS technology is used for active pixels, then the compatibility with peripheral circuits is improved, but the charge transfer reliability deteriorates
Solution Approach 1:
The storage node acts as an intermediary between the photodiode and the readout circuitry. It provides a stable holding point for accumulated charge, allowing reliable transfer through MOS transistors. This intermediary structure compensates for the inherently lower charge transfer reliability of MOS technology compared to CCD, as the storage node enables controlled, sequential charge transfer that maintains signal integrity.
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 approach enhances sensitivity and signal-to-noise ratio while maintaining conventional MOS technology, allowing for efficient image capture even at high object speeds without the need for complex pixel production techniques.
Implementation Method 1
Each pixel comprises a photodiode and a node for charge storage
Implementation Method 2
with a transfer gate adjacent to the photodiode and to the charge storage node so as to transfer the charge accumulated in the photodiode to the charge storage node
Data Source
AI summary
The invention relates to image sensors of scanner type observing one image line at a time. According to the invention, only two lines of pixels are used, operating in TDI mode (summation of the charge of two pixels seeing the same image point successively) but using active pixels with a charge-voltage conversion within the pixel. The pixels of like rank of the two lines each use a photodiode and a charge storage node with a transfer gate adjacent to the photodiode and to the storage node for transferring the charge accumulated in the photodiode to the charge storage node. The storage node is shared between the two pixels of like rank, and the charge of the two photodiodes is transferred successively into this node before the reading of the potential taken by the node. The time interval which separates the two charge transfers corresponds substantially to the time which separates the transit of an image line past the first line of pixels and then past the second.