Pixel OBS Voltage Timing for Low-Refresh Flicker Control
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Solution Overview
Problem
Display devices with variable refresh rate technology experience luminance deviations and increased flicker characteristics due to long data refresh cycles, particularly in low-speed driving, which affect image quality and grayscale expression.
Innovation Solution
A display device with a pixel circuit that includes an OBS control circuit to apply different levels of on-bias stress (OBS) voltages during refresh and skip frames, adjusting the OBS voltage levels to mitigate hysteresis effects and maintain optimal grayscale expression and reduce flicker.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the data refresh cycle is increased to reduce power consumption in low-speed driving, then power consumption decreases, but luminance deviation between frames increases and flicker characteristics worsen
Solution Approach 1:
The patent applies periodic on-bias stress (OBS) voltages to the driving transistor at specific intervals (before and after data voltage supply) to counteract hysteresis effects. This periodic intervention stabilizes the transistor's electrical characteristics across refresh frames, reducing luminance deviation while maintaining extended refresh cycles for power savings
Solution Approach 2:
The patent changes the electrical parameters (OBS voltage levels and timing) applied to the driving transistor to compensate for hysteresis-induced variations. By adjusting these parameters periodically, the system maintains stable luminance output even when operating at extended refresh cycles for lower power consumption
2Productivity
If the data refresh cycle is increased to implement low-speed driving, then productivity increases, but flicker characteristics deteriorate due to luminance deviation
Solution Approach 1:
The patent applies a first on-bias stress (OBS) voltage to the driving transistor before supplying the data voltage during refresh frames. This preliminary action prepares the transistor by reducing hysteresis effects in advance, ensuring stable luminance output during subsequent emission periods even when operating at extended refresh cycles
Solution Approach 2:
The patent implements a feedback mechanism where the timing and magnitude of OBS voltages are adjusted based on the refresh frame timing. This feedback control ensures that hysteresis compensation is applied at optimal moments, maintaining stable luminance characteristics during low-speed driving operations
Data Source
AI summary
A display device includes a display panel including a one pixel, a source driver configured to supply a data voltage to the pixel during a refresh frame, a scan driver configured to supply the pixel with a scan signal that defines a timing of a first on-bias stress (OBS) period that precedes a timing at which the data voltage is supplied to the pixel and a timing of a second OBS period that succeeds the timing at which the data voltage is supplied to the pixel and precedes an emission timing of the pixel, and an OBS control circuit configured to supply a first OBS voltage having a first level to the pixel during the first OBS period and supply a second OBS voltage having a second level that is different from the first level to the pixel during the second OBS period.