Variable Mobility Correction for OLED Screen Uniformity
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Solution Overview
Problem
Existing active matrix organic electroluminescence (EL) display devices face challenges in achieving uniform screen brightness due to variations in threshold voltage and mobility of thin film transistors, leading to non-uniformity in light emission across pixels, especially when optimal mobility correction time is not aligned with video signal levels.
Innovation Solution
The display device incorporates a pixel array section with sampling and drive transistors, holding capacitance, and a driving section that includes a write scanner and signal selector, which adjusts the input signal levels and control signal waveforms to vary the mobility correction period based on video signal levels, ensuring uniformity by canceling out variations in transistor mobility and threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed mobility correction period is used for all video signal levels, then the device complexity is reduced, but screen uniformity deteriorates due to variations in transistor mobility and threshold voltage
Solution Approach 1:
The patent applies dynamics by making the mobility correction period variable rather than fixed. The correction period is dynamically adjusted based on the video signal level (gray level) being displayed. For different gray levels, the correction period is optimized to compensate for mobility variations in the drive transistor, thereby improving screen uniformity without requiring complex external correction circuits.
Solution Approach 2:
The patent changes the parameter of correction period duration based on the video signal level. By adjusting the correction period parameter according to the gray level (0-255), the system optimizes mobility correction for each signal level. This parameter change approach allows the simple pixel circuit to achieve uniform screen display across different brightness levels.
2Manufacturing precision
If the mobility correction period is extended to cover the entire light emission period, then screen uniformity is improved, but power consumption increases
Solution Approach 1:
The patent implements periodic action by conducting mobility correction only during specific correction periods rather than continuously throughout the light emission period. The sampling transistor performs negative feedback correction during designated time intervals, which are optimized based on the video signal level. This periodic correction approach reduces power consumption compared to continuous correction while maintaining screen uniformity.
Solution Approach 2:
The patent applies partial action by performing mobility correction only for the duration necessary to achieve uniformity, rather than throughout the entire light emission period. The correction period is carefully controlled to be just long enough to compensate for mobility variations, avoiding excessive correction time that would increase power consumption unnecessarily.
3Device complexity
If the trailing edge waveform of the control signal is simplified to a fixed pattern, then device complexity is reduced, but the ability to optimize correction time for different signal levels is lost
Solution Approach 1:
The patent achieves multi-functionality by designing the output buffer to generate different trailing edge waveforms (first, second, and third patterns) using a unified circuit structure. The same buffer circuit can produce various waveform patterns by adjusting transistor switching timing, allowing the system to optimize correction time for different gray levels without requiring separate control signal generation circuits for each waveform type.
Data Source
AI summary
A display device includes a pixel array section and a driving section. The pixel array section includes scanning lines arranged in rows, signal lines arranged in columns, and pixels arranged in a matrix. Each of the pixels includes at least a sampling transistor, a drive transistor, a holding capacitance, and a light-emitting device. The sampling transistor has its control terminal connected to the scanning line and its pair of current terminals connected between the signal line and the control terminal of the drive transistor. The drive transistor has one of its pair of current terminals connected to the light-emitting device and the other of its pair of current terminals connected to a power source. The holding capacitance is connected between the control and current terminals of the drive transistor.