3T-4S Image Sensor Unit Cell Layout and Signal Routing
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Solution Overview
Problem
There is no existing solution for combining four image sensor unit cells each including three transistors into a single unit cell, limiting the layout and signal processing capabilities of image sensors.
Innovation Solution
A 3T-4S step & repeat unit cell is created by combining four image sensor unit cells, each with four transistors, where signals from two photodiodes are output through common detection lines, allowing for efficient two-dimensional arrangement and signal processing by distinguishing between green and red filter signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If four image sensor unit cells are combined into a single unit cell, then the layout efficiency and signal processing capability are improved, but the device complexity increases
Solution Approach 1:
The unit cell is segmented into four distinct photodiode regions (first, second, third, and fourth photodiodes) with dedicated transistor pairs for each, allowing independent signal capture while maintaining a unified compact structure. This segmentation enables efficient packing of four sensing elements within a single unit cell footprint.
Solution Approach 2:
Four separate image sensor unit cells are merged into a single integrated unit cell structure where multiple photodiodes and transistor pairs share common circuit elements and output pathways. The merging reduces overall device area while maintaining the functional capabilities of four independent sensing elements.
2Area of stationary object
If common detection lines are used for multiple photodiodes, then the peripheral circuit area is reduced, but the signal processing complexity increases
Solution Approach 1:
The common detection lines serve multiple functions by carrying signals from different photodiode pairs. The first common detection line OUT1 handles signals from the first and second photodiodes, while the second common detection line OUT2 handles signals from the third and fourth photodiodes, enabling multi-functional signal routing with reduced circuitry.
Solution Approach 2:
Conversion transistors act as intermediaries between the photodiode pairs and the common detection lines. These transistors condition and transfer signals from multiple photodiodes to shared output lines, managing the complexity of signal routing while minimizing the required peripheral circuit area.
3Quantity of substance
If reset and conversion transistors are shared between photodiode pairs, then the number of transistors per unit cell is reduced, but the control signal management becomes more complex
Solution Approach 1:
Reset transistors and conversion transistors are merged into shared components that serve multiple photodiode pairs. The first and second photodiodes share a common reset transistor and conversion transistor pair, while the third and fourth photodiodes share another common reset transistor and conversion transistor pair, reducing the total transistor count per unit cell.
Solution Approach 2:
The shared reset and conversion transistors are controlled by periodically activated control signals that enable them to serve different photodiode pairs at different time intervals. This periodic control allows the same hardware components to handle multiple sensing elements sequentially, reducing component count while managing signal complexity through time-multiplexed operation.
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 efficient signal processing and layout of image sensors by separating common detection lines for green and red filter signals, reducing the need for additional units and minimizing peripheral circuit area, thus enhancing system performance and reducing power consumption.
Implementation Method 1
a first photodiode PD0; a second photodiode PD1 disposed in a diagonal direction of the first photodiode PD0; a third photodiode PD2 disposed at a side of the second photodiode PD1; and a fourth photodiode PD3 disposed over the second photodiode PD1
Data Source
AI summary
A 3T-4S step & repeat unit cell obtained by combining four image sensor unit cells each including three transistors and a 3T-4S image sensor including the 3T-4S step & repeat unit cell are provided. The 3T-4S step & repeat unit cell includes first to fourth photodiodes. A first shared image sensor unit cell is obtained by combining the first and second photodiodes with four transistors. A second shared image sensor unit cell is obtained by combining the third and fourth photodiodes with four transistors. Signals corresponding to images incident onto the first and second photodiodes are output through a first common detection line. Signals corresponding to images incident onto the third and fourth photodiodes are output through a second common detection line. A terminal of each of the four photodiodes is connected to a first voltage source. Conversion voltages corresponding to image signals incident onto two photodiodes via green filters are output through a common detection line. Conversion voltages corresponding to image signals incident onto the other two photodiodes via red and blue filters are output through another common detection line.