Pixel Initialization Timing for Uniform OLED Display Luminance
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Solution Overview
Problem
In display devices using current drive type electro-optical elements, image quality defects such as horizontal bands and shading occur due to luminance differences caused by gate-anode coupling in pixel circuits with common power supplies during surface collective drive with timing shifts.
Innovation Solution
A display device design that includes a plurality of signal and control lines, each pixel with a light emitting element, capacitor, write transistor, drive transistor, light emission control transistor, and initialization transistor, where all initialization transistors are turned off before light emission control transistors turn on simultaneously, ensuring uniform luminance across stages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If surface collective drive with timing shifts is used, then power drop is reduced, but luminance difference occurs due to gate-anode coupling
Solution Approach 1:
The anode potential initialization is performed in advance before the light emission drive. By initializing the anode potential to a reference potential before applying the drive signal, the patent eliminates the luminance difference caused by gate-anode coupling while maintaining the timing shift configuration for power drop reduction.
2Ease of operation
If initialization transistor is kept on during light emission, then easy control is achieved, but holding potential difference occurs in each stage
Solution Approach 1:
The initialization transistor is controlled to turn off before the light emission drive starts. By performing the anode potential initialization in advance and then turning off the initialization transistor, the patent maintains potential uniformity across all stages while keeping the control mechanism simple.
3Device complexity
If common power supply is used, then device complexity is reduced, but luminance difference occurs due to stage timing shifts
Solution Approach 1:
The patent introduces an anode potential initialization step before the light emission drive in the common power supply configuration. This preliminary action equalizes the anode potential across all stages, eliminating luminance differences while maintaining the simple common power supply architecture.
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 configuration eliminates luminance differences and power drops, resulting in improved image quality and uniform luminance across the display panel.
Implementation Method 1
a capacitor, a write transistor that causes a voltage corresponding to a pixel signal supplied from a corresponding signal line among the plurality of signal lines to be accumulated in the capacitor
Implementation Method 2
an organic EL element using a phenomenon of emitting light when an electric field is applied to an organic thin film using electro luminescence (EL) of an organic material
Data Source
AI summary
A display device according to an aspect of the present disclosure includes a plurality of pixels and a drive unit, in which each of the plurality of pixels includes a light emitting element, a capacitor, a write transistor that causes a voltage corresponding to a pixel signal to be accumulated in the capacitor, a drive transistor that supplies a current corresponding to the voltage accumulated in the capacitor to the light emitting element, a light emission control transistor that controls whether or not to supply the current from the drive transistor to the light emitting element, and an initialization transistor in which one of a source node and a drain node is provided to be connectable to an anode of the light emitting element and the other is provided to be connectable to a cathode of the light emitting element, and the drive unit turns off the initialization transistors provided in all of the plurality of pixels at or before a timing at which the light emission control transistors provided in pixels that simultaneously emit light among the plurality of pixels are turned on.