OLED Pixel Circuit Decoupling Current from Threshold Voltage
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Solution Overview
Problem
In OLED displays, non-uniform threshold voltage of driving transistors leads to varying currents through different pixels, causing luminance inconsistencies and temporary afterimages due to hysteretic effects, resulting in non-uniform display effects.
Innovation Solution
A pixel circuit design incorporating a drive controlling sub-circuit, data writing sub-circuit, light-emission controlling sub-circuit, resetting sub-circuits, charging sub-circuit, and capacitor sub-circuit, where the driving current is made dependent on the data signal voltage rather than the threshold voltage of the drive controlling sub-circuit, ensuring uniform luminance across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional pixel circuit design is used, then the structure is simple, but the luminance uniformity deteriorates due to threshold voltage variations
Solution Approach 1:
The pixel circuit is divided into multiple functional sub-circuits: drive controlling sub-circuit, data writing sub-circuit, light-emission controlling sub-circuit, resetting sub-circuits, charging sub-circuit, and capacitor sub-circuit. Each sub-circuit performs a specific function to collectively solve the luminance uniformity problem while maintaining manageable complexity through modular design.
Solution Approach 2:
The capacitor sub-circuit acts as an intermediary to store and stabilize the voltage difference between the first node and the first voltage signal terminal. This intermediary component decouples the driving current from threshold voltage variations, ensuring that luminance depends on the data signal rather than transistor parameter variations.
2Reliability
If driving current depends on threshold voltage, then the circuit operation is simple, but temporary afterimages occur due to hysteric effects
Solution Approach 1:
The capacitor sub-circuit serves as an intermediary that stores the voltage difference, making the driving current dependent on the stored voltage rather than the real-time threshold voltage of the driving transistor. This eliminates the hysteric effects that cause temporary afterimages while maintaining straightforward circuit control through the established voltage relationship.
Solution Approach 2:
The capacitor is charged in advance during the charging period to establish a stable voltage difference before the light-emission period begins. This preliminary action ensures that the driving current is determined by the pre-established voltage rather than varying threshold voltages, preventing temporary afterimages without complicating the operational control.
3Ease of manufacture
If threshold voltage variations are present, then transistor manufacturing is easier, but luminance inconsistencies occur across different pixels
Solution Approach 1:
The capacitor sub-circuit acts as an intermediary that decouples the luminance output from the threshold voltage of the driving transistor. By storing the voltage difference, it ensures that luminance depends on the data signal and capacitor voltage rather than transistor manufacturing variations, allowing easier transistor fabrication without sacrificing luminance consistency.
Solution Approach 2:
The invention changes the controlling parameter for driving current from threshold voltage to capacitor-stored voltage. This parameter change allows standard transistor manufacturing processes to be used while achieving consistent luminance, as the capacitor voltage can be precisely controlled and is independent of transistor threshold voltage variations.
Data Source
AI summary
A pixel circuit, a method for driving the same, a display panel, and a display device are provided. The pixel circuit includes: a drive controlling sub-circuit, a data writing sub-circuit, a light-emission controlling sub-circuit, a first resetting sub-circuit, a second resetting sub-circuit, a charging sub-circuit, a capacitor sub-circuit, and a light-emitting element; and the respective sub-circuits cooperate in operation so that charges in the drive controlling sub-circuit in the pixel circuit can be reset, and driving current of the drive controlling sub-circuit to drive the light-emitting element to emit light can be made dependent upon the voltage of a data signal, and independent of threshold voltage of the drive controlling sub-circuit.