OLED Display Driving Circuit Vertical Blank Period Luminance Control
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Solution Overview
Problem
Organic light emitting diode (OLED) display devices experience image distortion due to luminance changes caused by frequency changes in the clock signal, particularly during the transition between frame periods, which affects the accuracy of gray level representation and overall image quality.
Innovation Solution
The implementation of a digital driving method that includes a vertical blank period within the frame period, allowing the timing controller to adjust the activation and vertical blank periods based on clock signal frequency, thereby minimizing luminance changes and reducing image distortion. This is achieved through a configuration of a display panel with row pixel blocks, a timing controller, a data driver, and a scan driver that manage data and scan signals in a way that maintains image stability during frequency changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a dual scan method is used to provide data signals to pixels in parallel by activating two scan signals concurrently, then the data writing time per pixel is enlarged enabling digital driving on larger OLED display devices, but image distortion occurs between divided regions
Solution Approach 1:
The display panel is divided into multiple regions (first region and second region) with different scan signal activation patterns. The first region uses scan signals activated during the front porch period while the second region uses scan signals activated during the sync active period, allowing parallel data writing while maintaining image quality in each segmented region.
Solution Approach 2:
Different scan control strategies are applied to different regions of the display panel. The first region receives scan signals with different timing characteristics compared to the second region, optimizing each region's performance for its specific location and reducing image distortion at region boundaries.
2Device complexity
If the analog driving technique is used to implement gray levels using voltage stored in storage capacitor of each pixel, then the display device can operate with simpler circuitry, but the gray level implementation is not accurate due to voltage variations
Solution Approach 1:
The patent employs a digital driving technique that divides each frame into multiple sub-frames with different light emitting times. By controlling the duration of light emission in each sub-frame and summing the emission times, accurate gray levels are achieved through time-based modulation rather than voltage storage, eliminating the gray level accuracy problems of analog driving.
3Adaptability or versatility
If frame period frequency is changed to adapt to different display requirements, then the display device can operate at different refresh rates, but luminance changes occur causing image distortion
Solution Approach 1:
The timing controller calculates the luminance level of the next frame during the vertical blank period based on the current frame's activation period characteristics. This feedback mechanism allows the system to predict and compensate for luminance changes when clock signal frequency varies, maintaining image stability across different refresh rates.
Solution Approach 2:
The luminance level of the next frame is calculated in advance during the vertical blank period before the next activation period begins. This preliminary calculation allows the system to prepare compensation parameters that will be applied during the next frame's display, preventing luminance distortion before it occurs.
Data Source
AI summary
An organic light emitting diode (OLED) display device includes: a display panel including a first through (2M)-th row pixel blocks; a data driver including a first data driving unit to provide N odd row data signals to (2K−1)-th row pixel blocks and a second data driving unit to provide N even row data signals to (2K)-th row pixel blocks; a scan driver including a first scan driving unit configured to provide (2K−1)-th scan signals to (2K−1)-th row pixel blocks and a second scan driving unit configured to provide (2K)-th scan signals to (2K)-th row pixel blocks. The first frame period includes an activation period and a vertical blank period. The first scan driving unit is configured to activate the (2K−1)-th scan signals sequentially in pulse form in an activation period.