Pixel Compensation Circuit for OLED Brightness Uniformity
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Solution Overview
Problem
OLED display devices face issues with non-uniform brightness due to threshold voltage drifting in driving transistors, leading to premature light emission and incomplete compensation, especially with longer power lines causing voltage drops.
Innovation Solution
A pixel compensation circuit with a light emitting device, driving module, reset module, reference voltage writing module, data voltage writing module, power voltage writing module, and light emitting control module, which includes transistors and capacitors to manage nodes and control signals, preventing early light emission by compensating for threshold voltage and power voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional pixel compensation circuit with four transistors is used, then the circuit structure is simple, but the OLED emits light too early during the reset stage causing incomplete compensation and poor image quality
Solution Approach 1:
The pixel compensation circuit is divided into multiple independent writing modules (reference voltage writing module, data voltage writing module, power voltage writing module) and separate control modules. Each module performs a specific function at a specific time, allowing the compensation process to be completed before light emission, thus preventing premature light emission while maintaining reasonable circuit complexity.
Solution Approach 2:
The circuit performs reference voltage writing, data voltage writing, and power voltage writing in advance during the reset and compensation stages before the light emitting stage. This preliminary action ensures that all compensation operations are completed before the OLED emits light, solving the problem of incomplete compensation.
2Area of stationary object
If the power line connected to pixels is made longer to cover larger display areas, then the display area is increased, but the voltage drop (IR Drop) increases causing non-uniform brightness
Solution Approach 1:
The power voltage writing module writes the actual power voltage value (which varies due to IR Drop) to the second node individually for each pixel or pixel group. This allows each region to compensate for its specific voltage drop, maintaining uniform brightness across the entire display area even with longer power lines.
Solution Approach 2:
The circuit measures and writes the actual power voltage value experienced by each pixel region back to the storage capacitor. This feedback mechanism allows the system to compensate for voltage drops dynamically, ensuring brightness uniformity across the display.
3Adaptability or versatility
If the threshold voltage of the driving transistor drifts, then the electrical performance changes, but the brightness uniformity deteriorates
Solution Approach 1:
The data voltage writing module writes the difference value between the data voltage and the threshold voltage to the first node during the compensation stage before light emission. This preliminary compensation for threshold voltage drift ensures that the OLED achieves uniform brightness despite transistor threshold variations.
Data Source
AI summary
A pixel compensation circuit and a display device are provided. The pixel compensation circuit includes a light emitting device, a driving module, a reset module, a reference voltage writing module, a data voltage writing module, a power voltage writing module, and a light emitting control module.