OLED Pixel Circuit Compensation for Threshold Voltage Drift
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Solution Overview
Problem
In organic light emitting diode (OLED) display devices, the variation in threshold voltages of thin-film transistor switches over time leads to differences in color intensity between adjacent pixels, causing aberrant color display as the devices age.
Innovation Solution
A pixel circuit design incorporating an organic light emitting diode (OLED), a driving switch, an enabling switch, a compensation circuit, and a data switch, where the compensation circuit sets the voltage at the driving switch's control terminal to equal the data voltage minus the absolute value of the threshold voltage, thereby decoupling the driving current from the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If thin-film transistor (TFT) fabrication is used to make transistor switches, then the display device can be manufactured with OLED technology, but the threshold voltage difference between transistor switches increases and changes with usage time
Solution Approach 1:
The compensation circuit performs preliminary action by measuring and storing the threshold voltage of the driving transistor before it causes display errors. The circuit proactively compensates for threshold voltage variations by adjusting the gate voltage of the driving transistor based on the stored threshold voltage value, preventing color display aberrations before they occur during normal operation
Solution Approach 2:
The compensation circuit implements feedback by continuously monitoring the threshold voltage of the driving transistor and using this information to adjust the driving voltage. The measured threshold voltage is fed back to the driving switch control, creating a closed-loop system that automatically compensates for threshold voltage drift over time and across different pixels
2Productivity
If the same data voltage is supplied to adjacent pixels, then the data transmission is simple and efficient, but the color intensity displayed by adjacent pixels becomes different due to threshold voltage variations
Solution Approach 1:
The compensation circuit applies local quality by providing individualized compensation to each pixel's driving transistor based on its specific threshold voltage characteristics. Each pixel has its own compensation circuit that measures and compensates for its local transistor's threshold voltage, allowing adjacent pixels with different threshold voltages to display uniform color intensity while maintaining simple data transmission
3Power
If the driving switch controls current based on gate voltage, then the OLED can be driven effectively, but threshold voltage changes cause the driving current to vary and produce color aberrations
Solution Approach 1:
The compensation circuit acts as an intermediary between the data voltage source and the driving switch. It introduces a compensating voltage that mediates the relationship between the fixed data voltage and the variable threshold voltage, ensuring that the driving current remains consistent despite threshold voltage changes. This intermediary compensation voltage adjusts the effective gate voltage to counteract threshold voltage drift
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design ensures consistent driving current for the OLED, independent of threshold voltage variations, maintaining uniform color intensity across pixels and reducing age-related aberrations in display devices.
Implementation Method 1
Organic light emitting diodes (OLED) have a smaller size and a high luminous efficiency and can be applied to flexible panels
Data Source
AI summary
A pixel circuit with an organic light emitting diode (OLED) includes an OLED, a driving switch, an enabling switch, a compensation circuit, and a data switch. Through the compensation circuit, the data switch, and the control of a compensation voltage, a voltage at the control terminal of the driving switch of the pixel circuit is set according to a data voltage and the absolute value of a threshold voltage of the driving switch. Hence, the driving current determined by the driving switch relates to the data voltage.