OLED Pixel Power Supply Segmentation for Leakage Control
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Solution Overview
Problem
In organic light-emitting displays, reducing the voltage of a second power supply to achieve low current emission can lead to black luminance issues and increased leakage current, affecting image quality due to the reduction in initialization power supply voltage.
Innovation Solution
The implementation of a separated third and fourth power supply system, where the third power supply initializes the gate electrode of the drive transistor and the fourth power supply initializes the anode electrode of the organic light-emitting diode, allowing for independent voltage control and minimizing leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the voltage of the second power supply is reduced to achieve high luminance, then luminance is improved, but leakage current increases and image quality deteriorates
Solution Approach 1:
The power supply system is segmented into multiple independent power supplies (first power supply ELVDD, second power supply ELVSS, third power supply Vint1, fourth power supply Vint2) with different functions. The third power supply initializes the gate electrode while the fourth power supply initializes the anode electrode, allowing independent voltage control to reduce leakage current while maintaining high luminance
Solution Approach 2:
Different power supplies are applied to different parts of the pixel circuit with specific voltage characteristics. The third power supply Vint1 is set to a higher voltage than the second power supply ELVSS to prevent leakage current in the gate electrode, while the fourth power supply Vint2 is set to a lower voltage than Vint1 but higher than ELVSS to prevent leakage in the anode electrode, creating localized voltage optimization
2Use of energy by moving object
If the voltage of the second power supply is reduced to achieve low current emission, then current consumption is reduced, but black luminance performance deteriorates
Solution Approach 1:
The power supply system is divided into multiple independent units with different voltage levels and functions. The first power supply ELVDD provides high voltage for high luminance emission, while the second power supply ELVSS operates at lower voltage for low current consumption during non-emission periods, with the third and fourth power supplies providing intermediate voltage levels for proper initialization of different circuit components
Solution Approach 2:
The pixel circuit dynamically switches between different power supply configurations based on operation mode. During emission, the first power supply ELVDD is activated for high luminance. During non-emission, the second power supply ELVSS operates at lower voltage to minimize current consumption while the third and fourth power supplies maintain proper voltage levels to prevent leakage and maintain black luminance performance
3Device complexity
If a single power supply is used for initialization, then device complexity is reduced, but leakage current increases due to voltage constraints
Solution Approach 1:
The initialization function is segmented into two separate power supplies: the third power supply Vint1 for initializing the gate electrode and the fourth power supply Vint2 for initializing the anode electrode. This segmentation allows each power supply to be optimized for its specific function, with Vint1 set to a higher voltage than ELVSS to prevent gate leakage and Vint2 set to a lower voltage than Vint1 but higher than ELVSS to prevent anode leakage, thereby reducing overall leakage current despite increased complexity
Data Source
AI summary
A display device includes a scan driver supplying a scan signal to scan lines, an emission control driver supplying an emission control signal to emission control lines, and a data driver supplying data signals to data lines coupled to pixels. Each pixel includes a drive transistor controlling an amount of current from a first power supply to a second power supply via an organic light-emitting diode, and three other transistors. The third transistor is turned on by a scan signal on a prior scan line and receives a voltage of a third power supply. The first and second transistors are turned on by a scan signal on a present scan line. The fourth power supply is different from the second and third power supplies, and the first and third transistors receive voltages of their respective power supplies through different power lines on different layers.