Pixel Circuit With Dual Emission Timing for Luminance Stability
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Solution Overview
Problem
Display devices experience luminance inversion phenomena due to variations in light emitting element initialization times when using dimming techniques that adjust light emitting periods based on set luminance levels, particularly when interpolation methods are used for non-representative luminance levels.
Innovation Solution
A pixel circuit design incorporating a first emission signal with a variable off-duty ratio and a second emission signal with a fixed off-duty ratio, along with specific voltage application and initialization times, to stabilize light emitting element operations and prevent luminance inversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the light emitting period is adjusted according to set luminance levels using interpolation methods, then power consumption is reduced, but luminance inversion phenomenon occurs at non-representative luminance levels
Solution Approach 1:
The patent divides the single emission signal into two separate emission signals: a first emission signal for controlling the driving transistor power voltage application time, and a second emission signal for controlling the light emitting element current application time. This segmentation allows independent optimization of each signal's duty ratio, enabling accurate luminance control without interpolation errors that cause luminance inversion.
Solution Approach 2:
The patent changes the parameter of emission signal duty ratio by introducing two distinct signals with different off-duty ratios. The first emission signal has an off-duty ratio optimized for driving transistor control, while the second emission signal has an off-duty ratio optimized for light emitting element control. This parameter differentiation resolves the luminance inversion issue by eliminating the need for interpolation-based luminance level adjustments.
2Loss of energy
If the light emitting period is shortened for dimming, then power consumption decreases, but the light emitting element initialization time becomes insufficient
Solution Approach 1:
The patent segments the emission control into two independent signals with different timing characteristics. The first emission signal maintains a longer off-duty ratio to ensure sufficient initialization time for the driving transistor, while the second emission signal is optimized for the light emitting element current application. This segmentation allows the light emitting period to be shortened for power savings while preserving adequate initialization time through the first emission signal's timing.
Solution Approach 2:
The first emission signal performs preliminary action by controlling the power voltage application to the driving transistor in advance, ensuring proper initialization before the second emission signal activates the light emitting element current. This preliminary voltage application ensures that the driving transistor is fully initialized even when the overall light emitting period is shortened for power consumption reduction.
3Device complexity
If a single emission signal is used for both driving transistor control and light emitting element control, then device complexity is reduced, but luminance control precision deteriorates
Solution Approach 1:
The patent segments the emission control function into two separate signals: the first emission signal specifically for driving transistor power voltage control, and the second emission signal specifically for light emitting element current control. This functional segmentation enables precise luminance control by optimizing each signal's duty ratio for its specific control target, overcoming the limitations of a single emission signal that must serve dual purposes.
Solution Approach 2:
The patent applies local quality by assigning different off-duty ratios to different emission signals based on their specific control requirements. The first emission signal has an off-duty ratio optimized for driving transistor initialization characteristics, while the second emission signal has an off-duty ratio optimized for light emitting element current control. This localized optimization of signal parameters achieves high luminance control precision without excessive device complexity.
Data Source
AI summary
A pixel circuit includes a light emitting element, a driving transistor, a first emission transistor applying a first power voltage to the driving transistor in response to a first emission signal, a second emission transistor applying the driving current to the light emitting element in response to a second emission signal, a first initialization transistor applying a first initialization voltage to an anode electrode of the light emitting element in response to the second emission signal, a data write transistor, a compensation transistor, a second initialization transistor, and a storage capacitor. A first off-duty ratio which is a ratio of a high voltage level period of the first emission signal in one frame is determined according to a set luminance level, and a second off-duty ratio which is a ratio of a high voltage level period of the second emission signal in the one frame is fixed.