OLED Pixel Circuit with Transfer Capacitor for Voltage Compensation
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Solution Overview
Problem
Existing emissive display devices with organic light emitting diode (OLED) technology face challenges in achieving efficient pixel compensation and operation due to limitations in the structure and functionality of driving transistors, particularly in flexible substrates where uniformity and reliability of display are compromised.
Innovation Solution
The implementation of a novel pixel structure that incorporates an n-type transistor as a driving transistor, utilizing multiple transistors and capacitors to manage voltage and current efficiently, including a transfer capacitor and storage capacitor, along with specific connections to compensation and scan lines, to ensure consistent emission and compensation periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional driving transistor structure is used in OLED displays, then the device complexity is reduced, but the pixel compensation and display uniformity deteriorate
Solution Approach 1:
The pixel circuit is segmented into multiple functional blocks: a driving transistor unit comprising the driving transistor and transfer capacitor, a compensation transistor unit comprising compensation transistors and compensation capacitor, and a control transistor unit comprising control transistors and storage capacitor. This segmentation allows each unit to be optimized independently for its specific function, improving overall display uniformity while managing complexity through modular design.
Solution Approach 2:
The driving transistor is configured as an n-type transistor that serves multiple functions: driving the light emitting diode, storing voltage through the transfer capacitor, and participating in compensation circuits. This multi-functionality reduces the need for separate dedicated components, maintaining device complexity at acceptable levels while improving display uniformity through enhanced compensation capabilities.
2Reliability
If an n-type transistor is used as the driving transistor, then the pixel compensation and display uniformity are improved, but the device complexity increases
Solution Approach 1:
The transfer capacitor is pre-charged during the programming period before the emission period begins. The compensation transistors and capacitor are pre-configured to compensate for threshold voltage variations and other parameters before they affect display uniformity. This preliminary action ensures optimal compensation efficiency without requiring complex real-time adjustment circuits.
Solution Approach 2:
The transfer capacitor acts as an intermediary element between the data line and the driving transistor gate, storing the programmed voltage and isolating the driving transistor from direct data line variations. The compensation capacitor and transistors serve as intermediaries that mediate threshold voltage compensation, simplifying the overall control logic while improving compensation efficiency.
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 improved pixel compensation and operation, ensuring uniformity and reliability in emissive display devices, particularly in flexible substrates, by maintaining constant voltage and adjusting emission current effectively, thereby enhancing display performance.
Implementation Method 1
a transfer capacitor including a first transfer electrode electrically connected to a second electrode of the second transistor and a second transfer electrode electrically connected to the driving gate electrode
Implementation Method 2
a light emitting diode including an anode and a cathode receiving an output current outputted to the second electrode of the driving transistor
Data Source
AI summary
Embodiments provide an emissive display device including a driving transistor including a first electrode, a second electrode, and a driving gate electrode, a second transistor including a first electrode electrically connected to a data line, a transfer capacitor including a first transfer electrode electrically connected to a second electrode of the second transistor and a second transfer electrode electrically connected to the driving gate electrode; a fifth transistor electrically connecting the first electrode of the driving transistor and the driving gate electrode; a ninth transistor including a second electrode electrically connected to the second electrode of the driving transistor; and a light emitting diode including an anode and a cathode receiving an output current outputted to the second electrode of the driving transistor.