Display Pixel Circuit With Capacitive Coupling for Luminance Stability
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Solution Overview
Problem
Display devices experience luminance reduction when switching from a low to high gradient, and there is a need to enhance response speed and accuracy in luminance representation.
Innovation Solution
The display device incorporates a pixel circuit with specific transistors and capacitors to manage voltage differences and apply reference voltages during different periods, including an initialization, sampling, coupling, and light emission periods, to mitigate luminance decay and enhance response speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional pixel circuit is used, then the device structure is simple, but luminance reduction occurs when switching from low to high gradient
Solution Approach 1:
The pixel circuit applies reference voltage to the gate electrode before the light emission period (in the first and third periods) to preliminarily set the transistor in a ready state. This preliminary action compensates for voltage changes that would otherwise cause luminance reduction during high-gradient transitions, ensuring stable luminance output when needed.
Solution Approach 2:
The driving period is segmented into five distinct periods (first through fifth periods) with different voltage application strategies. Each period serves a specific function: initialization, threshold setting, reference voltage application, high-potential voltage application, and light emission. This segmentation allows precise control of luminance throughout the cycle, particularly during critical transition phases.
2Speed
If the screen switches from low to high gradient quickly, then the response speed is fast, but luminance reduction occurs
Solution Approach 1:
The circuit preliminarily applies reference voltage to the gate electrode during the first and third periods before the actual light emission. This prepares the transistor in advance, so when a rapid gradient transition occurs, the transistor is already in an optimal state to deliver full luminance without reduction, thus maintaining both fast response and stable luminance.
Solution Approach 2:
The reference voltage is applied continuously across multiple periods (first, third, and implicitly maintaining through fifth period) to ensure the transistor remains in a stable, ready state throughout the entire cycle. This continuous preparation eliminates gaps where luminance reduction could occur during rapid transitions, maintaining uninterrupted useful action.
3Measurement precision
If the gate-to-source voltage is not compensated, then the circuit operation is simple, but accurate luminance representation is degraded
Solution Approach 1:
The capacitor connected between gate and source electrodes provides automatic feedback to maintain constant gate-to-source voltage. When voltage changes occur during switching, the capacitor compensates by releasing or storing charge, ensuring the gate-to-source voltage remains stable. This feedback mechanism enables accurate luminance representation without complex external control circuits.
Solution Approach 2:
The pixel circuit uses its own internal components (capacitor connected to gate and source) to self-compensate for voltage changes. The capacitor automatically adjusts the gate-to-source voltage based on circuit conditions during each period, eliminating the need for external voltage management circuits while maintaining precise luminance control.
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 effectively mitigates luminance decay and accelerates response speed by compensating for gate-to-source voltage changes and applying data voltages to maintain consistent luminance during gradient transitions.
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.