OLED PMOS Buffer Driving for Uniform Digital Gradation
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Solution Overview
Problem
Conventional organic light emitting displays face challenges in accurately expressing brightness gradations due to process deviations in transistor threshold voltages and electron mobilities, leading to non-uniform luminance and difficulty in achieving precise gradation control.
Innovation Solution
The implementation of a digital drive method using buffers with PMOS transistors for demultiplexers, which divides a frame into sub-frames and employs a data driver and scan driver to supply data signals and scan signals, respectively, while using buffers to minimize voltage loss and delay, allowing for precise control of pixel emission times to achieve uniform luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If analog driving with storage capacitor voltage is used to control pixel current, then the pixel circuit can be simple, but the brightness gradation expression becomes inaccurate due to transistor threshold voltage variations and electron mobility differences
Solution Approach 1:
The patent changes the control parameter from voltage (analog) to time (digital). By controlling the emission time duration of each pixel rather than using voltage levels, the system achieves accurate brightness gradation expression that is independent of transistor threshold voltage variations and electron mobility differences. This temporal control method transforms the problematic voltage-based analog system into a robust time-based digital system.
2Ease of manufacture
If process deviation in transistors is present, then manufacturing becomes feasible, but uniform luminance across pixels cannot be achieved due to varying threshold voltages and electron mobilities
Solution Approach 1:
The patent eliminates dependence on transistor electrical characteristics by changing from voltage control to time control. The emission duration of each pixel is precisely controlled through digital timing signals, making the luminance uniformity independent of threshold voltage and electron mobility variations caused by process deviations. This allows standard manufacturing processes to be used while achieving uniform display quality.
3Manufacturing precision
If digital drive with buffers and demultiplexers is implemented, then gradation accuracy and luminance uniformity improve, but device complexity increases
Solution Approach 1:
The patent segments the display frame into multiple sub-frames and divides the pixel array into blocks, with demultiplexers distributing data signals to different data lines. This segmentation allows the use of simpler buffer circuits and demultiplexers while achieving precise temporal control. The complexity is distributed and managed through systematic division rather than requiring a single complex control circuit.
Solution Approach 2:
The patent uses buffers to pre-charge data lines with data signals before the actual pixel selection occurs. This preliminary action ensures that when pixels are selected during the scan period, the data is already prepared and available, enabling precise timing control without requiring excessively complex real-time switching circuits. The demultiplexers are configured in advance to route signals appropriately.
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 enables more accurate expression of gradations and uniform luminance across pixels, improving drive performance and reducing manufacturing costs by using PMOS transistors and demultiplexers to control emission times rather than relying on constant voltage division.
Implementation Method 1
Organic light emitting displays make use of organic light emitting diodes (OLEDs) that emit light by re-combining electrons and holes
Data Source
AI summary
An organic light emitting display configured to be driven using a frame divided into a plurality of sub-frames includes a data driver configured to supply a plurality of data signals to output lines during a first period of one horizontal period of the sub-frame, a scan driver configured to sequentially supply a scan signal to scan lines during a second period of the one horizontal period of the sub-frame, a demultiplexer coupled to each output line, the demultiplexer being configured to supply the data signals to a plurality of data lines, buffers configured to supply buffers supplying signals from the demultiplexers to the data lines, the buffers including PMOS transistors, and pixels disposed at intersections of the scan lines and the data lines, the pixels being configured to display images corresponding to the data signals.