Pixel Circuit Using Global Signal Lines for High-PPI Threshold Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional pixel circuits with source follower structures face limitations in achieving high PPI and high resolution due to insufficient threshold voltage compensation and parasitic capacitor variations, leading to inaccurate luminance and inefficient operation.
Innovation Solution
A pixel circuit design incorporating fewer transistors and capacitors, utilizing a first global signal line for compensation and a second global signal line for initialization, allowing simultaneous gate signal application across multiple pixel circuits, reducing the need for additional scan drivers and minimizing dead space and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a source follower structure is used for threshold voltage compensation, then the pixel circuit can compensate for threshold voltage shifts, but the compensation time is insufficient and the compensation accuracy deteriorates due to parasitic capacitor variations
Solution Approach 1:
The patent performs threshold voltage compensation in advance during a dedicated compensation period before the emission period. The compensation transistor copies the threshold voltage of the driving transistor to the storage node during this preliminary phase, ensuring accurate compensation is established before data writing and emission occur, eliminating the need for continuous compensation during emission.
2Area of moving object
If the pixel circuit area is reduced to achieve high PPI and high resolution, then the integration density improves, but the threshold voltage compensation becomes insufficient
Solution Approach 1:
The patent extracts the compensation function from the traditional source follower structure and implements it through a dedicated compensation transistor that operates independently during a specific compensation period. This separation allows the pixel circuit to use fewer transistors and capacitors, reducing the overall area while maintaining effective threshold voltage compensation through the specialized compensation mechanism.
3Reliability
If additional scan drivers are added to improve threshold voltage compensation, then the compensation accuracy improves, but the device complexity and power consumption increase
Solution Approach 1:
The patent makes the compensation transistor and storage node serve multiple functions: they perform both threshold voltage compensation and data storage. The same storage node that holds the threshold voltage compensation value also stores the data voltage, eliminating the need for separate compensation and data storage paths, thereby reducing device complexity while maintaining compensation accuracy.
4Reliability
If the pixel circuit uses traditional source follower structure, then threshold voltage compensation is attempted, but the luminance accuracy deteriorates due to parasitic capacitor variations
Solution Approach 1:
The patent implements a feedback mechanism where the compensation transistor copies the threshold voltage of the driving transistor to the storage node during the compensation period. This feedback loop ensures that the storage node receives an accurate representation of the driving transistor's threshold voltage, compensating for variations and ensuring accurate luminance output during emission.
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A pixel circuit may include a first transistor including a control electrode connected to a first node, a first electrode receiving a first power supply voltage, and a second electrode connected to a second node, a second transistor including a control electrode receiving a writing gate signal, a first electrode receiving a data voltage, and a second electrode connected to a third node, a third transistor including a control electrode receiving a compensation gate signal, a first electrode connected to the first node, and a second electrode connected to the second node, a fourth transistor including a control electrode receiving an initialization gate signal, a first electrode connected to the second node, and a second electrode receiving an initialization voltage, a holding capacitor including a first electrode connected to the third node and a second electrode connected to the first node, and a light emitting element.