Inverted Emission Signal Circuit for Variable Refresh Rate Display
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In display devices operating in variable refresh rate mode, the difference in refresh rates leads to brightness variations between pixels, causing image quality degradation such as warpage or flicker.
Innovation Solution
A display device configuration that includes a transistor with a gate electrode receiving an inverted emission signal, forming a capacitor between an inverted emission line and a node of a pixel, thereby reducing on-bias stress of a driving transistor and improving charging/discharging delay of a light emitting element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If variable refresh rate mode is applied to drive pixels at various refresh rates, then power consumption is reduced and lifetime is extended, but brightness difference occurs between pixels causing image quality degradation
Solution Approach 1:
The patent applies preliminary action by initializing the light emitting element before the emission period begins. The initialization transistor applies an initialization voltage to the anode of the light emitting element in advance, ensuring it starts from a known state. This preliminary initialization prevents brightness variations that would otherwise occur during variable refresh rate transitions, thereby maintaining image quality while allowing power consumption reduction benefits.
Solution Approach 2:
The patent implements periodic action through the cyclic initialization and emission process. The initialization signal is applied periodically before each emission period, creating a regular pattern of voltage application to the light emitting element. This periodic initialization ensures consistent brightness characteristics across different refresh rates, resolving the image quality degradation issue while maintaining the power consumption advantages of variable refresh rate mode.
2Duration of action of stationary object
If variable refresh rate mode is applied to drive pixels at various refresh rates, then lifetime of display device is extended, but brightness difference occurs between pixels causing flicker
Solution Approach 1:
The initialization transistor performs preliminary action by setting the anode voltage of the light emitting element to a known state before emission begins. This preliminary voltage application prevents unpredictable brightness behavior during refresh rate transitions, eliminating flicker while preserving the extended lifetime benefits of variable refresh rate operation.
Solution Approach 2:
The patent employs feedback through the gate driver circuitry that receives emission signals and generates corresponding initialization signals. The timing and voltage levels of initialization signals are determined based on the emission signal characteristics, creating a feedback mechanism that ensures consistent light output across different refresh rates, thereby preventing flicker while maintaining device lifetime extension.
3Device complexity
If conventional emission signal configuration is used, then device structure is simple, but charging delay of light emitting element occurs upon low-frequency driving
Solution Approach 1:
The initialization transistor performs preliminary charging of the light emitting element before the emission period begins. By applying the initialization voltage in advance, the light emitting element is pre-charged to the required voltage level, eliminating charging delays that would otherwise occur during low-frequency driving. This preliminary action maintains simple device structure while significantly improving charging speed.
4Device complexity
If conventional emission signal configuration is used, then device structure is simple, but on-bias stress of driving transistor increases
Solution Approach 1:
The initialization transistor applies preliminary voltage to the light emitting element before the driving transistor needs to drive current through it. This preliminary voltage application reduces the voltage swing and current stress that the driving transistor must handle during emission, thereby reducing on-bias stress while maintaining simple device structure with only one additional transistor per pixel.
Data Source
AI summary
A display device includes a gate driver for applying a scan signal, an emission signal, and an inverted emission signal to the pixel circuits, in which the gate driver includes at least one scan driver for outputting the scan signal. The device includes a light emitting driver for outputting the emission signal, and inverting drivers of which at least some output an inverted emission signal of which phase is inverted from that of the emission signal using the scan signal output from the at least one scan driver and the emission signal output from the light emitting driver. Accordingly, the charging delay of the light emitting element upon the low-frequency driving in the variable refresh rate mode can be prevented and the characteristics and on-bias stress of the driving transistor can be adjusted.