Timing Controller Adjusts Gate Periods for OLED Luminance Uniformity
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Solution Overview
Problem
Organic light emitting diode (OLED) displays face issues with emission delay and color drag due to differences in driving current and parasitic capacitance between green, red, and blue LEDs, leading to inadequate luminance and visible defects like purple color in white display and afterimages, especially at low luminance.
Innovation Solution
The display device incorporates a timing controller that adjusts the gate-on and gate-off periods of scan and emission control signals based on dimming levels, controlling the bias holding time of driving transistors and parasitic capacitor discharge to synchronize current flow and improve luminance uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the organic light emitting diode outputting green light uses a smaller driving current to achieve higher luminous efficiency, then energy consumption is reduced, but the parasitic capacitance increases causing larger charge amount requirement and emission delay
Solution Approach 1:
The patent applies preliminary action by initializing the green sub-pixel with a higher voltage (e.g., 5V) before normal operation to pre-charge the parasitic capacitance. This preliminary charging action compensates for the delayed emission that would otherwise occur due to the larger capacitance, allowing the green pixel to emit light simultaneously with red and blue pixels when displaying white.
2Stability of the object's composition
If the driving transistor operates with hysteresis characteristic to maintain stability, then threshold voltage remains stable, but the current flowing through the pixel deviates from the set current causing luminance inaccuracy
Solution Approach 1:
The patent implements feedback by measuring the actual luminance output of each pixel and adjusting the driving current accordingly. The luminance sensing unit detects the actual luminance, and this information is fed back to the current control unit, which compensates for deviations caused by transistor hysteresis. This closed-loop control ensures that the pixel achieves the target luminance despite hysteresis effects.
3Illumination intensity
If the display device operates at low luminance to reduce eye strain, then user comfort improves, but emission delay and color drag become more visible causing display defects
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the initialization voltage and duration based on the displayed color and luminance level. For green pixels at low luminance, the system increases the initialization voltage and extends the initialization period to ensure proper charge accumulation. This adaptive parameter adjustment maintains display quality and reduces visible defects even at low overall luminance levels.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces emission delay and color drag, ensuring accurate color representation and minimizing afterimages by optimizing transistor bias states and current control across different luminance levels.
Implementation Method 1
an organic light emitting diode outputting green light has a higher luminous efficiency than an organic light emitting diode outputting red light or blue light
Implementation Method 2
a parasitic capacitance of the organic light emitting diode outputting green light and connected in parallel structurally may be larger than that of the organic light emitting diode outputting red light or blue light
Implementation Method 3
a driving transistor included in a pixel has a hysteresis characteristic in which a threshold voltage and a current of the driving transistor change based on a change of a gate voltage
Data Source
Figure 1
Figure 2A
Figure 2B~3
AI summary
A display device includes: a display panel including a plurality of pixels; a scan driver configured to supply a scan signal to the plurality of pixels through a plurality of scan lines based on a scan start signal; an emission driver configured to supply an emission control signal to the plurality of pixels through a plurality of emission control lines based on an emission control start signal; and a timing controller configure to control an interval between a plurality of gate-on periods of the scan start signal within a gate-off period of the emission control start signal based on a dimming level.