Dual-Gate Pixel Driving Circuit for Fast Display Grayscale Control
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Solution Overview
Problem
Display devices face a trade-off between high-speed driving and expression of various grayscales due to the limitations of driving transistor channels being either short or long, which affect on-current and driving range, respectively.
Innovation Solution
The display device incorporates a dual-gate driving transistor structure comprising a first and second driving transistor, allowing independent compensation of the threshold voltage of the first driving transistor, thereby maintaining high on-current for high-speed driving while widening the driving range for enhanced grayscale expression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-mobility electron transistor is used as the emission control transistor, then the transistor can be fully turned on during the emission period, but the channel off-state current increases due to hot carrier injection
Solution Approach 1:
The emission control transistor is divided into two separate transistors: a first emission control transistor with high-mobility semiconductor layer that handles the on-state current during emission, and a second emission control transistor with low-mobility semiconductor layer that controls the off-state current. This segmentation allows each transistor to be optimized for its specific function, resolving the contradiction between on-state performance and off-state leakage.
Solution Approach 2:
Different regions of the emission control circuit use transistors with different semiconductor layer properties. The first emission control transistor uses a high-mobility semiconductor layer (e.g., IGZO) for superior on-state characteristics, while the second emission control transistor uses a low-mobility semiconductor layer for better off-state control. This local differentiation of material properties solves the contradiction by assigning optimal characteristics to each functional requirement.
2Object-generated harmful factors
If a high-mobility electron transistor is used as the emission control transistor, then the channel off-state current is reduced, but the transistor cannot be fully turned on during the emission period
Solution Approach 1:
The emission control function is segmented between two transistors with complementary characteristics. The first transistor (high-mobility) ensures full turn-on capability during emission, while the second transistor (low-mobility) ensures low off-state current. This segmentation resolves the contradiction by distributing the conflicting requirements to different components.
Solution Approach 2:
The dual-transistor emission control circuit achieves universal emission control functionality by combining two transistors with different semiconductor layer properties. The circuit as a whole can both fully turn on during emission (via the high-mobility transistor) and maintain low off-state current (via the low-mobility transistor), making the system capable of satisfying both contradictory requirements simultaneously.
3Reliability
If the threshold voltage of the emission control transistor is lowered to fully turn on the transistor, then the on-state performance improves, but the off-state current increases
Solution Approach 1:
The emission control is segmented into two transistors where the first transistor (with lowered threshold voltage and high-mobility layer) provides full turn-on capability, while the second transistor (with higher threshold voltage and low-mobility layer) suppresses off-state current. This segmentation allows threshold voltage optimization for each function without compromise.
Solution Approach 2:
Different threshold voltage characteristics are applied locally to different transistors in the emission control circuit. The first transistor has a lowered threshold voltage for optimal on-state performance, while the second transistor has a higher threshold voltage for optimal off-state control. This local differentiation resolves the contradiction by matching threshold voltage properties to specific functional requirements.
Data Source
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AI summary
A display device includes a plurality of pixels each including: a first driving transistor including a first electrode connected to a first node; a second electrode connected to a second node, and a gate electrode connected to a third node, a second driving transistor including a first electrode connected to a fourth node, a second electrode connected to the first node, a gate electrode connected to the third node, and a lower gate electrode configured to receive an emission control signal; a second transistor including a first electrode configured to receive a data voltage, a second electrode connected to the first node, and a gate electrode configured to receive a write gate signal; and a third transistor including a first electrode connected to the second node, a second electrode connected to the third node, and a gate electrode configured to receive the write gate signal or a compensation gate signal.