OLED Brightness Uniformity via Dynamic Grayscale Control
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Solution Overview
Problem
Organic light emitting display devices face challenges in maintaining uniform brightness due to the rapid degradation of organic light emitting diodes when operated in a digital driving mode, leading to difficulties in displaying images with consistent brightness.
Innovation Solution
The method involves representing gray levels using subframes before degradation occurs and compensating for degradation by adjusting the light emitting time of pixels, utilizing a degradation compensator and timing controller to maintain constant brightness, and employing a dummy pixel to adjust bit values and light emitting periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If digital driving mode is used to drive organic light emitting diodes, then the display can operate with simple circuit control, but the organic light emitting diodes degrade rapidly causing non-uniform brightness
Solution Approach 1:
The patent applies dynamics by transitioning from static digital driving (fixed on/off states) to dynamic grayscale control through pulse width modulation. The organic light emitting diodes are driven with variable duty cycles representing different gray levels, allowing brightness control without rapid degradation. This dynamic approach maintains brightness uniformity while preserving circuit control simplicity.
Solution Approach 2:
The patent changes the driving parameter from binary digital states to analog-like grayscale values through duty cycle variation. By modifying the temporal parameter (duty cycle ratio of high to low periods) rather than using multiple voltage levels, the system achieves gradual brightness control that reduces diode stress and extends lifespan, thereby maintaining brightness uniformity.
2Device complexity
If constant voltage is applied to organic light emitting diodes, then the display can be driven simply, but the diodes degrade rapidly making it difficult to display images with uniform brightness
Solution Approach 1:
The patent employs periodic action through pulse width modulation, where constant voltage is applied intermittently rather than continuously. By varying the duty cycle (ratio of on-time to total period) for different pixels or time intervals, the system achieves grayscale control while reducing the cumulative stress on organic light emitting diodes, thereby preventing rapid degradation and maintaining brightness uniformity.
Solution Approach 2:
The patent maintains continuous useful action by using pulse width modulation to continuously adjust brightness levels across all pixels simultaneously. Rather than switching between discrete voltage levels, the system continuously varies the duty cycle parameters, enabling smooth grayscale transitions while keeping all diodes operating within safe stress limits, thus preserving brightness uniformity over time.
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 approach allows for the display of images with substantially uniform brightness by controlling the light emitting time of each pixel to compensate for organic light emitting diode degradation, effectively addressing the issue of non-uniform brightness.
Implementation Method 1
the organic light emitting display device displays an image by using organic light emitting diodes (OLEDs) that generate light by means of recombination of electrons and holes
Data Source
AI summary
A method of driving an organic light emitting display device including a plurality of pixels during a frame including subframes includes: representing gray levels by utilizing some of the subframes of the frame prior to degradation of an organic light emitting diode of each of the plurality of pixels; and compensating for the degradation of the organic light emitting diodes by changing the utilized subframes to increase a portion of the frame utilized by the plurality of pixels to represent the gray levels.