Scan Driver Signal Overlap for High-Frequency Display Stability
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Solution Overview
Problem
High-resolution organic light emitting displays face issues with abnormal scan signals due to shortened scan times, leading to irregular images when driven at frequencies of 120 Hz or higher, as the increased load on scan lines results in RC delay and insufficient compensation time.
Innovation Solution
A scan driver design that includes multiple stages receiving phase-delayed clock signals, outputting scan signals with a pulse width of two or more horizontal cycles, and overlapping these signals by one or more cycles to ensure stable image production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the scan frequency is increased to 120 Hz or higher for high-resolution displays, then the productivity and response speed of the display is improved, but the scan time is shortened causing abnormal scan signals and irregular images
Solution Approach 1:
The patent applies preliminary action by extending the pulse width of scan signals before they are transmitted to compensate for the shortened scan time at high frequencies. By pre-adjusting the signal duration to be two horizontal cycles or more, the invention ensures that pixels receive sufficient activation time even during fast scanning, preventing abnormal signals and maintaining image regularity at 120 Hz or higher scan frequencies
Solution Approach 2:
The patent implements beforehand cushioning by overlapping adjacent scan signals by one horizontal cycle or more. This overlap creates a time buffer that compensates for RC delays and ensures continuous pixel activation, providing a cushion against signal abnormalities that would otherwise occur at high scan frequencies, thus maintaining reliable image display
2Reliability
If the pulse width of scan signals is increased to prevent abnormal signals, then the reliability of image display is improved, but the scan time is extended reducing the maximum scan frequency
Solution Approach 1:
The patent applies partial or excessive action by setting the scan signal pulse width to at least two horizontal cycles, which is longer than the minimum single-cycle width traditionally used. This excessive duration ensures reliable pixel activation and prevents abnormal signals at high frequencies, while the signal overlap optimization ensures that this extended width does not significantly reduce the maximum achievable scan frequency
3Manufacturing precision
If the number of horizontal lines is increased for high resolution, then the manufacturing precision and quality of the display is improved, but the RC delay on scan lines increases causing signal abnormalities
Solution Approach 1:
The patent applies preliminary action by pre-extending the pulse width of scan signals to two horizontal cycles or more before transmission. This pre-compensation accounts for the increased RC delay caused by higher resolution displays with more horizontal lines, ensuring that pixels receive sufficient activation time despite the longer signal transmission duration required by extended scan lines
Solution Approach 2:
The patent implements beforehand cushioning by overlapping adjacent scan signals by one horizontal cycle or more. This overlap creates a time buffer that compensates for RC delays in high-resolution displays, ensuring continuous pixel activation and preventing signal abnormalities even as the number of horizontal lines increases
Data Source
AI summary
A scan driver is coupled to a plurality of scan lines and includes a plurality of stages. Each of the stages is configured to sequentially receives clock signals that are phase delayed by two horizontal cycles or more from three of a plurality of clock lines, and output a scan signal having a pulse width of two horizontal cycles or more to a corresponding scan line. The scan signals are overlapped with each other by one horizontal cycle or more.