OLED Pixel Circuit Stabilizes Driving Current via Anode Decoupling
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Solution Overview
Problem
In organic electroluminescent display apparatuses using N-type transistors, the luminance of light emitted by the pixels is unstable due to variations in voltage levels, leading to deteriorated image quality, as the voltage of the anode affects the driving current and thus the luminance of the OLEDs.
Innovation Solution
A pixel circuit design incorporating N-type transistors with specific configurations, including a driving transistor, diode-connected transistors, and a capacitor, which initializes the gate electrode and anode to specific voltages, allowing the data signal to be delivered through a series of transistors to stabilize the driving current output to the OLED, independent of the anode voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If N-type transistors are used to form the organic electroluminescent display apparatus, then the device complexity is reduced and manufacturing is simplified, but the luminance stability deteriorates due to voltage level variations affecting the anode voltage and driving current
Solution Approach 1:
The patent introduces a capacitor as an intermediary element between the anode and the driving transistor. This capacitor decouples the anode voltage from the driving current, preventing voltage fluctuations from directly affecting the luminance. The capacitor acts as a buffer that isolates the sensitive driving current from voltage variations in the power supply network.
Solution Approach 2:
The patent changes the electrical parameters by introducing a specific capacitor value (typically 50-200 fF) to compensate for voltage variations. By adjusting the capacitance parameter, the circuit can maintain stable driving current despite changes in anode voltage, thus stabilizing luminance output.
2Adaptability or versatility
If the anode voltage is allowed to vary with power supply fluctuations, then the circuit operates more flexibly, but the driving current and luminance become unstable
Solution Approach 1:
The capacitor serves as a mediator that allows the circuit to adapt to power supply variations while maintaining stable luminance. It absorbs voltage fluctuations from the power supply, enabling flexible operation across different power conditions without compromising image quality.
3Device complexity
If no compensation mechanism is used, then the device simplicity is maintained, but image quality deteriorates due to luminance variations from voltage changes
Solution Approach 1:
The capacitor provides a simple yet effective compensation mechanism that significantly improves image quality by eliminating luminance variations. This single component solution maintains circuit simplicity while achieving the desired image quality, avoiding the need for complex active compensation circuits.
Data Source
AI summary
An organic electroluminescent display apparatus including a pixel circuit and a method of driving the organic electroluminescent display apparatus are provided. Embodiments of the present invention may solve problems where the luminance of light is changed due to a change of a voltage of an anode of an organic electro-light emitting device such that an image quality is deteriorated when N-type transistors are used to form the organic electroluminescent display apparatus.