OLED Pixel Circuit Leakage Current Suppression
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Solution Overview
Problem
Organic light emitting display devices face reduced contrast ratio and display quality due to increased leakage current, particularly with crystalline silicon thin film transistors, which is more severe than in LCDs, affecting the display of black images.
Innovation Solution
The implementation of a display pixel structure that includes a capacitor, switching transistor, emission control transistor, driving transistor, and light-emitting device, where specific scanning signals control the transistors to minimize current through the light-emitting device during black image display, thereby bypassing leakage current and improving contrast ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a crystalline silicon thin film transistor is used as the driving transistor, then the device can achieve better electrical characteristics and stability, but the leakage current increases and the contrast ratio decreases
Solution Approach 1:
An emission control transistor is introduced as an intermediary component between the driving transistor and the light-emitting device. This additional transistor acts as a mediator that can independently control the current path to the light-emitting device, allowing the system to suppress leakage current while maintaining the stability benefits of crystalline silicon TFTs.
Solution Approach 2:
The current control function is segmented into two independent parts: the driving transistor controls the main drive current, while the emission control transistor separately manages the current to the light-emitting device. This segmentation allows independent optimization of each component's function, enabling leakage current suppression without sacrificing driving transistor stability.
2Illumination intensity
If the driving transistor outputs current to the light-emitting device, then the display can show image luminance, but leakage current during black image display reduces contrast ratio
Solution Approach 1:
The emission control transistor dynamically adjusts the current path to the light-emitting device based on display requirements. During black image display, the emission control transistor closes the current path to suppress leakage, while during luminance display, it opens the path to allow proper current flow, thus dynamically adapting to different display states.
Solution Approach 2:
The emission control transistor converts the potentially harmful leakage current into a beneficial controlled current path. By providing an alternative controlled path through the emission control transistor, the system can redirect what would be harmful leakage current into a useful path that maintains display quality.
3Device complexity
If a simple pixel structure is used, then the device complexity is reduced, but the ability to bypass leakage current is limited
Solution Approach 1:
The emission control transistor serves multiple functions: it controls current to the light-emitting device during normal operation, suppresses leakage current during black display, and works cooperatively with the driving transistor to maintain display quality. This multi-functionality justifies the additional component by providing multiple benefits from a single addition.
Data Source
AI summary
The present invention relates to a display device and a driving method thereof. A display device in the present invention comprises: a capacitor connected between a first node and a second node; a switching transistor controlled by a first scanning signal and transmitting a data voltage to the first node; an emission control transistor controlled by a second scanning signal and transmitting a reference voltage to the second node; a driving transistor comprising a control terminal connected to the first node, an output terminal connected to the second node, and an input terminal; a driving control transistor controlled by a third scanning signal and transmitting a driving voltage to the input terminal of the driving transistor; and a light-emitting device connected to the second node. Accordingly, display contrast of a display device may be improved.