Pixel Circuit Voltage Compensation for OLED Brightness Uniformity
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Solution Overview
Problem
Existing organic light-emitting display devices experience uneven display brightness due to differences in current flowing through light-emitting diodes caused by power voltage drops during voltage transmission between pixel circuits.
Innovation Solution
A pixel circuit comprising seven thin film transistors, a storage capacitance, and a light-emitting diode, where the current flowing through the LED is independent of the power voltage, compensated by data and reference voltages, ensuring consistent current flow and mitigating the effects of power voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the same power source supplies power voltage to multiple pixel circuits, then the power distribution is simplified, but IR drop occurs causing uneven display brightness
Solution Approach 1:
The power supply system is segmented into multiple independent power sources, with each pixel circuit having its own dedicated power source. This segmentation eliminates the IR drop problem caused by shared power lines, as each pixel receives stable power voltage directly from its own power source, ensuring uniform display brightness across all pixels.
2Device complexity
If power voltage is transmitted through shared lines to multiple pixel circuits, then the circuit design is simplified, but voltage drop causes current difference in LEDs
Solution Approach 1:
A compensation circuit is introduced as an intermediary between the power source and the LED to compensate for voltage drops. The compensation circuit includes compensation transistors and capacitors that generate compensation signals to counteract the IR drop effects, ensuring consistent current flow through LEDs even when using shared power lines.
3Ease of manufacture
If a simple pixel circuit structure is used, then manufacturing is easier, but threshold voltage variations cause display non-uniformity
Solution Approach 1:
Threshold voltage compensation is performed in advance during the pixel circuit operation. Compensation transistors and capacitors are configured to pre-calculate and compensate for threshold voltage variations before they affect the display output. This preliminary compensation action ensures uniform display brightness despite variations in transistor threshold voltages during manufacturing.
Data Source
AI summary
Exemplary embodiments of the application disclose pixel circuits and driving methods thereof, display devices. A pixel circuit includes a first through seventh thin film transistors, a light-emitting diode, and a storage capacitance. The pixel circuit provided by exemplary embodiments of the application can compensate a power voltage during a light-emitting stage of the light-emitting diode, so that the current flowing through the LED is related to a data voltage and a reference voltage input into the pixel circuit, and is independent of the power voltage, thereby effectively avoiding the problem of the display unevenness of the display device, due to the difference in the current flowing into the LED caused by the power voltage drop.