Scan Driver Overlap for OLED Threshold Voltage Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In organic light emitting display devices, the variation in threshold voltage of driving transistors leads to uneven luminance across pixels, and high-frequency driving further complicates sufficient threshold voltage compensation.
Innovation Solution
The implementation of a scan driver that supplies overlapping scan signals and emission control signals, along with a pixel circuit including multiple transistors and capacitors, allows for extended threshold voltage compensation periods, ensuring consistent luminance even under high-frequency operation and accounting for OLED degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the driving transistor is driven at a high frequency of over 120 Hz to remove motion blur, then the response speed is improved, but the period for storing the threshold voltage is shortened, making sufficient compensation impossible
Solution Approach 1:
The scan signal is extended to overlap with the previous scan line's signal, creating a preliminary action period where the compensation capacitor can store the threshold voltage before the normal data writing period. This preliminary action ensures that the compensation is completed in advance, allowing high-frequency driving without sacrificing compensation accuracy.
Solution Approach 2:
The patent introduces an additional time dimension by extending the scan signal duration into the next horizontal period. Instead of completing compensation within the traditional single horizontal period, the solution utilizes the overlapping time period between consecutive scan lines to achieve the required compensation storage time.
2Duration of action of moving object
If the scan signal width is extended to at least 2H to ensure sufficient compensation period, then the threshold voltage compensation is improved, but the horizontal period is extended, potentially reducing the driving frequency
Solution Approach 1:
The patent merges the compensation period with the existing horizontal scanning period by making the scan signal overlap with the previous scan line. This combining approach allows the compensation to occur during the natural transition between scan lines, so that extending the scan signal to 2H does not actually extend the total horizontal period beyond what is already required for normal display operation.
Solution Approach 2:
The solution utilizes the periodic nature of scan line activation, where each scan line is activated in sequence. By making the scan signal periodic and overlapping with the previous period, the system creates a rhythm where compensation can be stored during the overlap without disrupting the overall periodic driving frequency.
Data Source
AI summary
An organic light emitting display device includes a scan driver, a data driver, and pixels. The scan driver is for sequentially supplying, during each horizontal period of a width 1H, a scan signal with a width of at least 2H to scan lines. The scan driver is further for sequentially supplying an emission control signal to emission control lines that are substantially parallel to the scan lines. The data driver supplies data signals to data lines. Each pixel includes an organic light emitting diode (OLED), a pixel circuit having a first transistor for controlling the amount of current supplied to the OLED, and a compensator for controlling the voltage of a gate electrode of the first transistor for compensating a degradation of the OLED. The compensator includes two transistors and a capacitor. One transistor is coupled to a scan line, and the other is coupled to an emission control line.