OLED Pixel Driving Circuit with Threshold Voltage and IR-Drop Compensation
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Solution Overview
Problem
Organic light emitting diode (OLED) display devices face uneven display due to threshold voltage drift of driving transistors and IR-drop in power supply lines, leading to variations in pixel brightness and image quality.
Innovation Solution
An OLED pixel driving circuit is designed with a pixel capacitor, driving transistor, and multiple transistors to compensate for threshold voltage drift and IR-drop, using a reference voltage and data voltage to generate a constant driving current for the OLED, independent of power supply voltage and transistor threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pixel driving circuits are used, then the circuit structure is simple, but threshold voltage drift and IR-drop cause uneven display luminance
Solution Approach 1:
The pixel circuit is segmented into multiple functional modules: a pixel capacitor divided into first and second capacitors, multiple transistors (first, second, third, fourth transistors) with distinct functions. Each segment handles specific tasks such as voltage storage, threshold compensation, and light emission control, allowing the circuit to address threshold voltage drift and IR-drop independently while maintaining overall simplicity
Solution Approach 2:
The circuit performs preliminary compensation actions by storing reference voltages and threshold voltage differences in the pixel capacitor before the actual light emission process. The first transistor stores reference voltage, and the third transistor stores the difference between data voltage and threshold voltage, preparing the circuit to compensate for drift and IR-drop effects during operation
2Reliability
If threshold voltage compensation is implemented, then display uniformity improves, but circuit complexity increases
Solution Approach 1:
The circuit merges threshold voltage compensation and IR-drop compensation functions into a single integrated pixel circuit structure. The pixel capacitor stores both reference voltage and threshold voltage difference, and the transistors perform multiple functions including compensation, switching, and light emission control, reducing overall circuit complexity while achieving dual compensation
3Illumination intensity
If IR-drop compensation is added, then brightness uniformity across the panel improves, but the circuit becomes more complex
Solution Approach 1:
The circuit implements feedback compensation by storing the difference between data voltage and threshold voltage in the pixel capacitor through the third transistor. This feedback mechanism automatically adjusts for threshold voltage drift and IR-drop effects, ensuring consistent driving current and brightness uniformity across the display panel without requiring external compensation circuits
Data Source
AI summary
An organic light emitting diode pixel driving circuit includes a pixel capacitor for storing a received voltage and coupling a change valve of the voltage at a first electrode thereof to a second electrode thereof; a first transistor for providing a reference voltage to the first electrode of the pixel capacitor under the control of a first light emitting signal; a third transistor for transmitting a data voltage to second electrode of the pixel capacitor under the control of the first scanning signal; and a fourth transistor; thereby overcoming the uneven display of the entire image, which is caused by the drift of the threshold voltage of the driving transistor and the different driving current driving the different OLEDs to emit light when the different OLEDs receive the same image data signal, the different driving current is caused by the difference the high-level power supply voltages.