OLED Pixel Circuit Compensation for Display Uniformity
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Solution Overview
Problem
The brightness of organic light emitting diode (OLED) pixels in existing display technologies is affected by the threshold voltage of the driving transistor and the power supply voltage, leading to uneven display due to manufacturing process drifts and IR Drop issues.
Innovation Solution
A pixel circuit with a compensation unit and a driving method that isolates the operating current of the OLED from the threshold voltage of the driving transistor and the power supply voltage by using a 9T1C or 10T1C structure, including transistors and a storage capacitor, where the operating current is dependent only on the data signal voltage and a reference voltage, independent of the threshold voltage and power supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional pixel circuit with a driving transistor and storage capacitor is used, then the circuit structure is simple, but the brightness is affected by threshold voltage drift and power supply voltage variations leading to uneven display
Solution Approach 1:
The pixel circuit is divided into multiple functional modules: a compensation unit with sampling transistors to measure threshold voltage, a compensation capacitor to store the measured voltage, and a driving transistor. This segmentation allows independent compensation of threshold voltage drift and power supply variations, resolving the display uniformity issue while maintaining reasonable circuit complexity
Solution Approach 2:
The compensation unit samples the threshold voltage of the driving transistor and feeds back a compensated voltage to the compensation capacitor. This feedback mechanism continuously corrects for threshold voltage drift and power supply variations, ensuring stable brightness and uniform display across the panel
2Ease of operation
If the operating current depends on threshold voltage and power supply voltage, then the circuit operation is straightforward, but manufacturing process drifts cause brightness variations
Solution Approach 1:
Before the driving transistor operates to produce light, the compensation unit performs preliminary sampling of the threshold voltage and stores the compensated voltage in the compensation capacitor. This preliminary action ensures that subsequent driving operations are based on corrected parameters, improving brightness stability without complicating the actual driving operation
Solution Approach 2:
The compensation mechanism continuously samples and feeds back threshold voltage information to adjust the operating current. This feedback loop compensates for manufacturing drifts and power supply variations, ensuring reliable and stable brightness throughout the display's operational life
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 solution ensures that the operating current of the OLED is independent of the threshold voltage and power supply voltage, thereby stabilizing the brightness and preventing uneven display issues caused by manufacturing process drifts and IR Drop.
Implementation Method 1
an organic light emitting diode, connected between a first power supply and a second power supply
Data Source
AI summary
The present disclosure provides a pixel circuit and a driving method thereof, and an organic light emitting display apparatus. The pixel circuit includes: first to ninth transistors, a storage capacitor and a light emitting diode. T2 is used as a driving transistor, T3 is used as a switching transistor, T1, T2 and T3 form a threshold voltage sampling unit of T2, and T4, T8 and T9 form a compensation unit, and the compensation unit is used for compensating the IR Drop generated by a power supply voltage on a line.