Pixel Control Circuit for OLED Luminance Uniformity
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Solution Overview
Problem
Existing pixel control circuits face issues with luminance nonuniformity due to varying transistor characteristics and system voltage differences across pixels, leading to inconsistent brightness and image quality degradation over time, as well as residual charges affecting black image display.
Innovation Solution
A pixel control circuit comprising an organic light emitting diode, a switch, a driving transistor, a driving circuit, a compensation circuit, and a discharge circuit, which uses control signals to manage the electrical connections and provide a discharge path, thereby isolating the current flow from transistor threshold voltage variations and ensuring uniform brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the pixel control circuit uses a simple driving transistor configuration, then the device complexity is low, but luminance nonuniformity occurs due to transistor characteristic variations
Solution Approach 1:
The pixel control circuit is segmented into multiple functional modules: driving transistor T1B for current control, compensation transistor T1C for threshold voltage compensation, switching transistors T1A/T1D for signal routing, and capacitor C1 for voltage storage. Each module performs a specific function, allowing the circuit to address luminance uniformity without requiring complete redesign of the entire circuit.
Solution Approach 2:
The compensation transistor T1C acts as an intermediary element that senses and compensates for threshold voltage variations of the driving transistor T1B. By introducing this intermediate compensation mechanism, the circuit isolates the driving transistor from the effects of manufacturing variations, thereby maintaining luminance uniformity across different pixels.
2Area of stationary object
If the system voltage OVDD is transmitted through long transmission lines to different pixels, then the display area can be large, but voltage drops occur due to resistance causing luminance nonuniformity
Solution Approach 1:
The circuit design ensures that each pixel receives a stable reference voltage level despite variations in transmission line resistance. The compensation mechanism actively adjusts voltages to maintain equipotential conditions at each pixel location, effectively canceling out the effects of voltage drops in long transmission lines and ensuring uniform luminance across large display areas.
3Duration of action of moving object
If the organic light emitting diode retains charges after previous image display, then the energy storage can maintain brightness, but residual charges cause black images to appear not dark enough
Solution Approach 1:
The discharge transistor T1E is periodically activated during specific timing phases to discharge residual charges from the organic light emitting diode. This periodic discharge action occurs in synchronization with the image refresh cycle, allowing the diode to retain charges during normal operation for brightness maintenance while periodically clearing residual charges to ensure accurate black image display.
Data Source
AI summary
A pixel control circuit includes an organic light emitting diode, a driving transistor, a driving circuit, a discharge circuit and a compensation circuit. The driving transistor is used to turn on or turn off the organic light emitting diode. The discharge circuit is used to control the electrical connection between the organic light emitting diode and an initial voltage to timely provide a discharge path for the organic light emitting diode. The compensation circuit is used to compensate a conducting current for the organic light emitting diode when the organic light emitting diode emits light so that the conducting current is independent of a threshold voltage of the driving transistor. The driving circuit is used to control the electrical connection between a predetermined voltage and the driving transistor to make the organic light emitting diode emit light.