Variable Frequency Driving for OLED Luminance Uniformity
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Solution Overview
Problem
In organic light emitting display devices, process variations and voltage drops lead to differences in threshold voltage and mobility of driving thin film transistors, causing luminance differences between pixels, which can result in mura patterns, reduced lifetime, and image sticking, necessitating a compensation circuit to address these issues.
Innovation Solution
A display device employing a variable frequency driving method using a first and second frequency, with a timing controller controlled by separate clock signals from signal generators, and a pixel circuit comprising specific transistors and capacitors to manage scan and data signals, ensuring compensation for transistor differences and voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the driving frequency is increased to improve productivity, then the output per unit time increases, but the compensation time for transistor characteristics becomes insufficient, leading to luminance differences and image quality degradation
Solution Approach 1:
The patent implements dynamic frequency adjustment by providing multiple clock signals with different frequencies to the scan driver. The system can switch between a first clock signal (higher frequency) and a second clock signal (lower frequency) based on operational requirements. This dynamic frequency control allows the display device to optimize between productivity and image quality by selecting appropriate driving frequencies for different operating conditions.
2Reliability
If the driving frequency is decreased to secure compensation time, then the luminance uniformity improves, but the productivity and output per unit time decrease
Solution Approach 1:
The patent employs periodic action by alternately using different clock signal frequencies. The scan driver can switch between the first clock signal and the second clock signal in a periodic manner or based on specific conditions. This allows the system to periodically perform compensation operations at lower frequencies to maintain luminance uniformity while maintaining higher productivity when uniformity requirements are less critical.
3Reliability
If a compensation circuit is added to correct transistor characteristics, then the luminance difference between pixels is reduced, but the device complexity increases
Solution Approach 1:
Instead of adding complex compensation circuits, the patent changes the operational parameters (clock signal frequencies) to achieve compensation. By adjusting the driving frequency and providing different clock signals, the system can allocate sufficient time for compensation operations without requiring additional hardware components. This parameter-based approach maintains luminance uniformity while avoiding increased device complexity.
Data Source
AI summary
A display device includes: a plurality of pixels, where each of the pixels includes a light emitting device and a pixel circuit coupled to the light emitting device; a scan driver which supplies a scan signal to the pixel circuit; a data driver which supplies a data signal to the pixel circuit; a power supply which supplies a voltage to the pixel circuit; a timing controller which controls the scan driver; a first signal generator which provides a first clock signal to the timing controller; and a second signal generator which provides a second clock signal to the timing controller.