OLED Pixel Circuit with Secondary Transistor for Startup Current Control
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Solution Overview
Problem
The sudden application of high voltage to OLED display devices causes electric shock to the organic layer, leading to deterioration of OLED characteristics during the initial stages of display operation.
Innovation Solution
A pixel circuit design that includes a switching transistor, a capacitor for storing data signals, a first driving transistor for generating a primary driving current, and a second driving transistor that is activated during display stoppage to generate a secondary, reduced current, which is supplied to the OLED, thereby mitigating the electric shock and controlling brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high voltage is applied to OLED display device at the beginning of display operation, then display operation can be initiated, but electric shock is caused to the organic layer leading to deterioration of OLED characteristics
Solution Approach 1:
The patent applies preliminary action by introducing a preliminary current (second driving current) that flows through the OLED before the main driving current (first driving current). This preliminary current is generated by a second driving transistor that is turned on before the first driving transistor during the initial display operation period. By pre-conditioning the OLED with this smaller preliminary current, the organic layer is gradually activated without sudden high voltage shock, thus preventing deterioration while enabling fast response operation.
2Illumination intensity
If high voltage is applied to OLED display device, then light emission can be achieved, but electric shock damages the organic layer
Solution Approach 1:
The patent implements beforehand cushioning by using a second driving transistor that generates a preliminary driving current to cushion the shock before the main driving current is applied. This second transistor is activated first and provides a gradual current increase, acting as a protective buffer that prevents the harmful electric shock effect on the organic layer while still achieving the required brightness for light emission.
3Device complexity
If a single driving transistor is used, then device complexity is reduced, but the OLED cannot be protected from electric shock during initial operation
Solution Approach 1:
The patent applies segmentation by dividing the driving function into two separate transistors: a first driving transistor for generating the main driving current during normal operation, and a second driving transistor for generating the preliminary driving current during initial operation. This segmentation allows each transistor to be optimized for its specific function, with the second transistor specifically dedicated to the protection function during startup, thereby preventing electric shock damage while maintaining reliable OLED operation.
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
The secondary current, ranging from 0.01% to 1% of the primary current, effectively reduces the electric shock and prevents OLED deterioration, extending the device's lifetime by maintaining optimal brightness levels even during non-operation periods.
Implementation Method 1
an organic light emitting diode (OLED) for emitting light in response to at least one of the first driving current or the second driving current
Data Source
AI summary
A pixel circuit of an organic light emitting diode (OLED) display device is provided, which supplies a small current to an organic light emitting diode during stoppage of a display operation. The pixel circuit includes a second driving transistor, which is coupled in parallel with a first driving transistor. A gate control line is used to control the second driving transistor so that a small current can flow into the organic light emitting diode during the stoppage of the display operation. The small current is supplied through the second driving transistor to the organic light emitting diode during the stoppage of the display operation. Thus, the pixel circuit of the OLED display device can reduce or prevent an electric shock applied to the organic light emitting diode at the beginning of the display operation, thereby reducing or preventing deterioration of the characteristics of the organic light emitting diode.