Pixel Circuit Threshold Compensation for Display Devices
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Solution Overview
Problem
Display devices face challenges in accurately compensating for data voltage due to varying threshold voltages of driving transistors, especially at higher resolutions and driving frequencies, leading to potential image quality issues and increased manufacturing costs with multiple data lines.
Innovation Solution
The display device incorporates a specific configuration of transistors and capacitors, including dual gate transistors, and a method of operating these components to accurately sample and compensate for threshold voltages, separating compensation and data write periods, and initializing voltages to minimize afterimages and improve image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the resolution and driving frequency of the display device are increased, then the image quality and responsiveness are improved, but the data write period becomes narrower and data voltage compensation becomes insufficient
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: a driving transistor for current control, a first storage capacitor for threshold voltage compensation, and a second storage capacitor for data voltage storage. This segmentation allows simultaneous data writing and threshold compensation within the same time period, resolving the contradiction between high driving frequency and sufficient compensation time.
Solution Approach 2:
The circuit performs threshold voltage compensation in advance during the data write period by storing the threshold voltage on the first storage capacitor before the emission period begins. This preliminary action ensures that when data is written, the compensation is already in place, enabling high-speed operation without sacrificing compensation accuracy.
2Manufacturing precision
If multiple data lines are added to improve data voltage compensation, then the compensation accuracy is improved, but the manufacturing cost increases
Solution Approach 1:
The existing data line is made multi-functional by designing the pixel circuit to simultaneously perform data writing and threshold voltage compensation through it. The first storage capacitor captures the threshold voltage while the second storage capacitor stores the data voltage, both through the same data line interface. This eliminates the need for separate compensation lines, reducing device complexity while maintaining compensation accuracy.
Solution Approach 2:
The pixel circuit performs self-compensation by using its own transistors and capacitors to automatically capture and store the threshold voltage of the driving transistor during the data write period. This self-service mechanism eliminates the need for external compensation circuits or additional control lines, simplifying the overall device structure while ensuring accurate compensation.
3Manufacturing precision
If the data write period is extended to improve compensation, then the compensation accuracy is improved, but the image refresh rate decreases
Solution Approach 1:
The circuit enables continuous operation by performing both threshold voltage compensation and data writing simultaneously during the data write period. The first storage capacitor continuously holds the threshold voltage while the second storage capacitor continuously stores the data voltage, allowing the emission period to begin immediately without extending the write period, thus maintaining high refresh rates.
Solution Approach 2:
The pixel circuit dynamically switches between different operational modes within the data write period: initially capturing the threshold voltage on the first storage capacitor, then storing the data voltage on the second storage capacitor. This dynamic operation allows both compensation and data writing to occur in sequence within the same time period, preventing any extension of the overall write period and maintaining high image refresh rates.
Data Source
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AI summary
A display device includes a first transistor including a first electrode connected to a first power line, a second electrode connected to a third node, and a gate electrode connected to a first node, a first capacitor formed between the first power line and a second node, a second capacitor formed between the first node and the second node, an emission transistor including a first electrode connected to the third node, a second electrode, and a gate electrode connected to an emission control line, and a light emitting element connected to the second electrode of the emission transistor and a second power line.