OLED Scan Driving Circuit for Threshold Voltage Drift Compensation
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Solution Overview
Problem
Active matrix OLEDs experience threshold voltage drift due to stress and high temperatures, leading to varying brightness across the display panel, which affects image display quality.
Innovation Solution
A scan driving circuit with cascaded scan driving units that generate three types of shift scanning signals by adjusting the duty cycles of clock signals, specifically a 40% duty cycle for the first clock signal and 50% for the second, to compensate for threshold voltage drift and stabilize brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TFT is stressed and high temperature for a long period during using, then threshold voltage drift occurs, but display brightness uniformity deteriorates
Solution Approach 1:
The patent applies preliminary action by generating compensation signals in advance that anticipate and counteract the threshold voltage drift caused by stress and high temperature. The scan driving circuit pre-calculates and applies compensation values before the drift fully manifests, thereby maintaining display brightness uniformity despite the environmental stress conditions.
2Reliability
If compensation signal is added to original signal, then threshold voltage drift is compensated, but circuit complexity increases
Solution Approach 1:
The patent merges the compensation function into the existing scan driving circuit by integrating compensation signal generation within the scan driving units. Instead of adding separate compensation circuits, the invention combines threshold voltage compensation with the scanning signal generation process, thereby achieving compensation without proportionally increasing overall circuit complexity.
Solution Approach 2:
The scan driving units are designed to perform multiple functions: generating scan signals and simultaneously generating compensation signals. This multi-functionality allows the same circuit structure to serve dual purposes, reducing the need for additional dedicated compensation circuits and thereby limiting the increase in device complexity.
3Adaptability or versatility
If duty cycle of clock signals is adjusted, then three types of shift scanning signals are generated, but signal timing complexity increases
Solution Approach 1:
The patent changes the duty cycle parameter of the clock signals to generate different types of scan signals. By varying the duty cycle (e.g., 50% for first scan signal, 25% for second scan signal, 75% for third scan signal), the circuit can produce multiple signal types from a single clock source, achieving adaptability without requiring multiple separate signal generation circuits.
Data Source
AI summary
A scan driving circuit for OLED and a display panel are provided. The scan driving circuit for OLED comprising a plurality of scan driving units connected in cascade. The scan driving units at each stages for receiving the stage transmission signal at previous-stage, the first scan signal at previous-stage, the first scan signal at next-stage, the first clock signal and the second clock signal, and outputting a stage transmission signal at current-stage, the first scan signal at current-stage, the second scan signal at current-stage and the third scan signal at current-stage, wherein duty cycle of the first clock signal and the second clock signal are difference. The invention could generating three types shift scanning signal required for pixel compensation circuit and solved the problem of threshold voltage drift, then reducing difference brightness of display and enhancing display effect.