OLED Driving Method Alternating Constant-Voltage and Current
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Solution Overview
Problem
Organic light emitting displays (OLEDs) suffer from non-uniform luminance due to varying deterioration rates of organic light emitting diodes across pixels, leading to inconsistent image display as they age.
Innovation Solution
Implementing a driving method that alternates between a constant-voltage system and a constant-current system within a frame period, with the second time period being wider, to control the operation of driving transistors and power sources, ensuring uniform deterioration of OLEDs across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant-current system is used for driving pixels, then luminance uniformity is maintained, but OLED deterioration varies across pixels leading to non-uniform luminance over time
Solution Approach 1:
The patent applies dynamics by transitioning the pixel driving system between two operational states: constant-current mode and constant-voltage mode. The driving transistor is dynamically switched between saturation region and linear region operation based on the time period within the frame, allowing the system to adapt its characteristics to achieve both luminance uniformity and uniform deterioration across pixels.
Solution Approach 2:
The patent implements periodic action by dividing each frame into two distinct time periods: a first time period where pixels are driven in constant-current system, and a second time period where pixels are driven in constant-voltage system. This periodic switching between driving modes ensures that OLEDs experience both constant-current stress and constant-voltage stress over time, leading to uniform deterioration characteristics while maintaining luminance uniformity during the constant-current period.
2Stability of the object's composition
If a constant-voltage system is used for driving pixels, then OLED deterioration is uniform across pixels, but luminance uniformity deteriorates over time
Solution Approach 1:
The patent uses dynamics by allowing the pixel driving system to switch between constant-voltage mode (linear region operation) and constant-current mode (saturation region operation). During the second time period, the constant-voltage driving provides uniform stress to all OLEDs ensuring uniform deterioration, while during the first time period, the constant-current driving maintains luminance uniformity, thus dynamically balancing both requirements.
Solution Approach 2:
The patent applies periodic action by alternating between constant-voltage driving (second time period) and constant-current driving (first time period) within each frame. This periodic alternation ensures that OLEDs receive uniform voltage stress during the constant-voltage period for consistent deterioration, while maintaining luminance uniformity during the constant-current period, thereby resolving the contradiction over time.
3Measurement precision
If driving transistors operate in saturation region, then current control is precise, but power consumption increases
Solution Approach 1:
The patent implements periodic action by switching the driving transistor between saturation region operation (first time period) and linear region operation (second time period). During the first time period, saturation region operation provides precise current control for accurate luminance display. During the second time period, linear region operation reduces power consumption while still maintaining uniform OLED deterioration through constant-voltage driving.
Solution Approach 2:
The patent applies dynamics by dynamically changing the operating region of the driving transistor based on the time period within the frame. The transistor transitions between saturation region (high current control precision) and linear region (lower power consumption) operation, allowing the system to optimize the trade-off between current control precision and power consumption at different times during the display refresh cycle.
Data Source
AI summary
The present invention relates to a driving method of an organic light emitting display which is capable of displaying images at uniform luminance. A driving method of an organic light emitting display of an embodiment according to the present invention includes supplying a data signal to a pixel and, after the data signal is supplied, driving the pixel in a constant-voltage system during a first time period and in a constant-current system during a second time period.