OLED Bypass Transistor for Black Luminance Control
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Solution Overview
Problem
Existing organic light emitting diode (OLED) display devices face challenges in efficiently managing driving current for black image display, leading to poor contrast ratios due to the distribution of minimum driving current as bypass current, which affects image expression.
Innovation Solution
The OLED display device incorporates a bypass transistor that redirects a part of the minimum driving current to a path other than the organic light emitting diode, allowing for precise expression of black luminance by controlling the bypass current, thereby enhancing the contrast ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If minimum driving current is distributed as bypass current, then the OLED can be protected from excessive current, but the contrast ratio deteriorates due to poor black image expression
Solution Approach 1:
The bypass transistor is configured to dynamically control the bypass current based on the grayscale value. During black image display (low grayscale), the bypass transistor is turned off or minimally conductive to prevent current leakage that would degrade black expression. During white image display (high grayscale), the bypass transistor is fully conductive to protect the OLED from excessive current. This dynamic adjustment resolves the contradiction between OLED protection and contrast ratio maintenance.
Solution Approach 2:
The invention changes the conduction parameter of the bypass transistor based on the operating conditions. By controlling the gate voltage of the bypass transistor according to the grayscale signal, the bypass current is adjusted to be minimal during black display and maximal during white display. This parameter change allows the system to achieve both OLED protection and high contrast ratio.
2Reliability
If bypass current is increased to protect OLED, then OLED reliability improves, but black image expression deteriorates
Solution Approach 1:
The bypass transistor's conduction state is dynamically adjusted based on the grayscale value. During black image display, the bypass transistor is kept in an off state or minimal conduction state, allowing the OLED to achieve true black expression without current leakage. During white image display, the bypass transistor is turned on to provide current protection. This dynamic control eliminates the trade-off between reliability and black image expression.
Solution Approach 2:
The invention applies different bypass current levels to different operating conditions. Instead of using a fixed bypass current, the system locally adapts the bypass current magnitude based on the specific display requirement - minimal bypass current for black images and maximal bypass current for white images. This local quality adjustment resolves the contradiction between OLED protection and black image expression.
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 solution enables exact implementation of black images by managing the bypass current effectively, improving the contrast ratio and display quality of the OLED display device.
Implementation Method 1
An electron injected from one electrode and a hole injected from the other electrode are coupled with each other in the organic emission layer to generate an exciton, and the exciton emits energy to emit light.
Data Source
AI summary
An organic light emitting diode display device includes a semiconductor on a substrate with a driving channel, an auxiliary storage electrode on the substrate with a storage electrode formed of a same material as the semiconductor and separated therefrom, a first insulating layer covering the semiconductor and the auxiliary storage electrode, a driving gate electrode overlapping the auxiliary storage electrode to define an auxiliary storage capacitor, a second insulating layer covering the driving gate electrode and the first insulating layer, a main storage electrode overlapping the driving gate electrode to define a main storage capacitor, a passivation layer covering the data wire and the second insulating layer, a pixel electrode on the passivation layer, an organic emission layer on the pixel electrode, and a common electrode on the organic emission layer.