Display Device Initialization Voltage Offset for Luminance Uniformity
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Solution Overview
Problem
Display devices, such as OLEDs, often experience unsatisfactory image/video quality due to pixels emitting light of insufficient luminance, caused by shifted threshold voltages and hysteresis in driving transistors, leading to non-uniform luminance and afterimages.
Innovation Solution
A method and display device that involves providing an initialization voltage with different voltage levels for each frame period to offset and maintain the initialization voltage levels for driving transistors, ensuring consistent luminance and minimizing hysteresis effects by alternating offset directions between frame periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed initialization voltage is provided to the gate electrode of the driving transistor, then the device complexity is reduced, but the luminance uniformity deteriorates due to threshold voltage shifts and hysteresis effects
Solution Approach 1:
The patent applies dynamics by making the initialization voltage variable rather than fixed. The voltage level is dynamically adjusted based on the frame period number, transitioning between different voltage levels (e.g., first voltage level for even frame periods, second voltage level for odd frame periods) to compensate for threshold voltage shifts and hysteresis effects, thereby maintaining luminance uniformity without significantly increasing control complexity
Solution Approach 2:
The patent changes the parameter of initialization voltage level based on operational conditions (frame period). By alternating between multiple discrete voltage levels depending on whether the frame period is even or odd, the system adapts to cumulative threshold voltage shifts and minimizes hysteresis effects, improving luminance uniformity while keeping the voltage control mechanism relatively simple
2Device complexity
If the initialization voltage is offset in the same direction for consecutive frame periods, then the control mechanism is simple, but afterimages and luminance non-uniformity increase
Solution Approach 1:
The patent applies inversion by alternating the direction of voltage offsets between consecutive frame periods. Instead of consistently offsetting in the same direction, the system offsets in opposite directions (e.g., positive offset for even frame periods, negative offset for odd frame periods), which counteracts cumulative hysteresis effects and minimizes afterimage phenomena, thereby improving image quality without requiring complex control logic
Data Source
AI summary
A method of operating a display device may include the following steps: in a first frame period, before turning off a gate initialization transistor, changing an initialization voltage from a first level to a second level and subsequently returning the initialization voltage to the first level; in a second frame period, before turning off the gate initialization transistor, changing the initialization voltage from the first level to the second level and/or a third level and subsequently returning the initialization voltage to the first level. The display device may include the gate initialization transistor and a driving transistor. A first electrode the gate initialization transistor may receive the initialization voltage. A second electrode of the gate initialization transistor may be electrically connected to a gate electrode of the driving transistor. The first level, the second level, and the third level may be unequal to each other.