Pixel Circuit Voltage Coupling for Stable OLED Luminance
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Solution Overview
Problem
Display devices experience luminance reduction when switching from a low to high gradient, due to degradation of the driving transistor and hysteresis effects, leading to decreased response speed and inaccurate luminance representation.
Innovation Solution
A display device with a pixel circuit that includes a driving transistor, capacitors, and transistors configured to manage voltage differences and reference voltages through specific operational periods, mitigating luminance decay and enhancing response speed by initializing, sampling, coupling, and applying high-potential voltages during light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional pixel circuits are used, then device simplicity is maintained, but luminance reduction occurs when switching from low to high gradient
Solution Approach 1:
The pixel circuit applies a high-potential voltage to the source electrode before the light emitting element emits light (in the fourth period before the fifth period). This preliminary voltage application prepares the driving transistor to operate in saturation mode, ensuring stable luminance output when switching from low to high gradient displays, thereby preventing luminance reduction without adding complex external components
Solution Approach 2:
The pixel circuit dynamically switches between different operational periods (first through fifth periods) with different voltage configurations. The circuit transitions from initialization and sampling modes to a high-potential voltage application mode, allowing the driving transistor to adapt its operating state dynamically. This dynamic operation ensures the transistor maintains saturation during light emission, resolving the luminance stability issue while keeping the device structure relatively simple
2Speed
If conventional pixel circuits are used, then device complexity is low, but response speed decreases during gradient switching
Solution Approach 1:
The pixel circuit operates through five distinct periodic phases: initialization period, sampling period, first coupling period, second coupling period, and light emission period. Each period performs a specific function to prepare the driving transistor for optimal performance. This periodic operation structure enables fast response speed during gradient switching by systematically resetting and preparing voltage levels in each cycle, while the complexity is contained within the time-domain sequencing rather than spatial complexity
Solution Approach 2:
The pixel circuit functionality is segmented into multiple independent operational periods, each handling a specific task (initialization, sampling, coupling, voltage application, light emission). This temporal segmentation allows each phase to be optimized independently for speed while the overall structure remains manageable. The segmentation of functions into distinct time periods achieves fast response without requiring a complex simultaneous multi-component structure
3Measurement precision
If conventional pixel circuits are used, then manufacturing simplicity is maintained, but luminance representation accuracy deteriorates
Solution Approach 1:
The pixel circuit uses the capacitor to store and maintain the gate-source voltage difference of the driving transistor throughout the operational periods. This voltage storage mechanism provides feedback control, ensuring that the driving transistor operates at the correct voltage level during light emission. The feedback mechanism improves luminance representation accuracy by compensating for voltage variations and transistor degradation, while implementing this feedback within the existing pixel circuit framework maintains manufacturing simplicity
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
The solution effectively mitigates luminance decay and accelerates response speed by compensating for gate-to-source voltage decreases and preventing hysteresis effects, ensuring accurate luminance representation and improved performance during gradient changes.
Implementation Method 1
a capacitor connected with the gate electrode of the driving transistor and the drain electrode of the first transistor
Implementation Method 2
a voltage of the gate electrode of the driving transistor varies due to a coupling phenomenon of the capacitor
Data Source
AI summary
A display device includes a pixel circuit connected to a light emitting element. The pixel circuit includes a driving transistor having a gate electrode, a source electrode, and a drain electrode, and a capacitor connected with the gate electrode. The pixel circuit is driven according to a first period when a reference voltage is applied to the gate electrode, a second period when a gate-source voltage difference of the driving transistor is a threshold voltage of the driving transistor, a third period when the reference voltage is applied to the capacitor, and a voltage of the gate electrode varies due to a coupling phenomenon of the capacitor, a fourth period when a high-potential voltage higher than the reference voltage is applied to the source electrode, and a fifth period when the driving transistor is turned on to cause the light emitting element to emit light.