OLED Pixel Circuit Driving Method for Brightness Uniformity
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Solution Overview
Problem
Organic light-emitting diode (OLED) display devices suffer from residual image and motion image blurring phenomena due to the hysteresis characteristics of thin film transistors (TFTs) and voltage drops in driving voltage lines, leading to display deterioration and brightness inconsistencies.
Innovation Solution
The implementation of a driving method that includes a storage capacitor and multiple switch elements to manage the voltage across OLED elements, using scanning signals to control the flow of data and reset voltages, thereby minimizing hysteresis effects and maintaining consistent brightness across the display panel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a storage capacitor is added to maintain voltage, then brightness uniformity is improved, but device complexity increases
Solution Approach 1:
The pixel circuit is divided into multiple functional components: a driving TFT for current control, a storage capacitor for voltage maintenance, and multiple switch elements (first and second switch TFTs) for selective voltage application. This segmentation allows each component to perform its specific function optimally while working together to achieve brightness uniformity.
Solution Approach 2:
The storage capacitor is charged in advance during the programming period before the light emitting period. By performing this preliminary action, the voltage is ready to be maintained during the subsequent light emitting period, ensuring stable brightness without requiring continuous active control.
2Reliability
If multiple switch elements are used to control voltage, then residual image phenomenon is reduced, but device complexity increases
Solution Approach 1:
The circuit configuration dynamically changes based on the operational period. During the programming period, the first switch TFT is on and the second switch TFT is off, allowing data voltage to be applied. During the light emitting period, the first switch TFT is off and the second switch TFT is on, allowing reference voltage to be applied. This dynamic switching eliminates residual image effects by properly resetting the pixel circuit state.
Solution Approach 2:
The circuit uses feedback mechanisms where the storage capacitor maintains the gate voltage of the driving TFT, and the switch elements provide feedback control by selectively connecting either data voltage or reference voltage to the pixel circuit based on the operational phase, ensuring consistent performance.
3Reliability
If data voltage is applied continuously, then motion image blurring is reduced, but voltage drop compensation becomes difficult
Solution Approach 1:
The voltage application is performed periodically in distinct phases: during the programming period, data voltage is applied to update the pixel state; during the light emitting period, reference voltage is applied to maintain stable operation. This periodic action pattern allows the circuit to adapt to voltage drops by switching between different voltage levels at appropriate times.
Solution Approach 2:
The circuit changes the voltage parameter dynamically by switching between data voltage and reference voltage based on the operational period. This parameter change allows the system to compensate for voltage drops in the data line by using the reference voltage during the light emitting period when stable operation is critical.
Data Source
AI summary
An organic light-emitting diode display device includes a first switch element turned-on in response to a first scanning signal during a first period to supply a data to a first node, and then maintaining an off-state during a second period, a driving device adjusting a current through an organic light-emitting diode element in accordance with a voltage of the first node; a reference voltage source providing a reference voltage that is capable of turning-off the driving device, a second switch element maintaining an off-state during the first period, and turned-on during the second period to supply the reference voltage to the first node, and a storage capacitor maintaining the voltage at the first node.