OLED Pixel Circuit Double Gate Transistor Leakage Reduction
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Solution Overview
Problem
Organic light emitting diode display devices experience leakage currents and decreased luminance at high temperatures due to shifted threshold voltages, degrading display quality.
Innovation Solution
A pixel circuit with a double gate structure for transistors and application of a negative bias voltage to the second gate electrode of certain transistors to reduce leakage currents, including specific configurations for transistors and capacitors to manage power and initialization voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the organic light emitting diode display device is driven at high luminance and high temperatures, then the luminance output is improved, but the threshold voltage of the transistor shifts causing increased leakage current and decreased reliability
Solution Approach 1:
The patent applies preliminary action by initializing the transistor threshold voltage before the pixel circuit operates at high temperatures. The initialization circuit pre-compensates for the expected threshold voltage shift that occurs during high-temperature operation, ensuring the transistor maintains proper electrical characteristics throughout the display device's operation lifecycle.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the threshold voltage of the transistor based on operating conditions. The initialization circuit modifies the threshold voltage parameter in response to temperature and luminance conditions, compensating for drift and maintaining stable transistor operation during high-temperature, high-luminance driving scenarios.
2Reliability
If the threshold voltage of the transistor shifts at high temperatures, then the leakage current increases, but the luminance decreases
Solution Approach 1:
The patent implements feedback through the initialization circuit that continuously monitors and adjusts the transistor threshold voltage. The circuit uses feedback from the pixel circuit's operational state to detect threshold voltage shifts and applies compensating voltages to maintain stable transistor characteristics, preventing leakage current increase and luminance degradation during high-temperature operation.
3Device complexity
If a conventional pixel circuit structure is used, then the device complexity is low, but the leakage current and afterimage performance deteriorate at high temperatures
Solution Approach 1:
The patent applies segmentation by dividing the pixel circuit into distinct functional blocks: the main pixel circuit for driving the OLED and a separate initialization circuit for threshold voltage compensation. This segmentation allows the initialization circuit to specifically address high-temperature reliability issues without interfering with the normal operation of the pixel circuit, improving afterimage performance while maintaining manageable device complexity.
Data Source
AI summary
A pixel circuit includes an OLED, a first transistor including a gate electrode connected to a first node and an electrode connected to a third node, a capacitor including a first electrode for receiving a power supply voltage and a second electrode connected to the first node, a third transistor including a gate electrode for receiving a first gate signal, a first electrode connected to the first node, and a second electrode connected to the third node, a fourth transistor including a gate electrode for receiving a second gate signal, a first electrode connected to the first node, and a second electrode and a second gate electrode for receiving a first initialization voltage, and a seventh transistor including a gate electrode for receiving a third gate signal, a first electrode for receiving a second initialization voltage, and a second electrode connected to an anode electrode of the OLED.