OLED Pixel Circuit Gate Voltage Stabilization
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Solution Overview
Problem
In organic light emitting display devices, the threshold voltage variation of driving transistors leads to non-uniform current flow, causing display non-uniformity and luminance changes across pixels due to diode-connected current paths affecting gate electrode voltage.
Innovation Solution
A pixel design with additional transistors and capacitors is implemented to maintain uniform voltage at the gate electrode of the driving transistor, including a series connection of second transistors between the gate electrode and initialization power, and a capacitor between the common node and a constant voltage source, ensuring stable current flow and luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the driving transistor is diode-connected to compensate threshold voltage variation, then display uniformity is improved, but current paths form between the gate electrode and power sources causing gate voltage changes and luminance non-uniformity
Solution Approach 1:
The pixel circuit is divided into multiple independent transistor components (first transistor for current control, second transistor for voltage stabilization, third transistor for initialization). This segmentation allows each transistor to perform a specific function without interfering with others, resolving the conflict between achieving display uniformity and maintaining gate voltage stability.
Solution Approach 2:
A capacitor is introduced as an intermediary element connected between the gate electrode of the first transistor and a reference potential. This capacitor acts as a voltage stabilizer that decouples the gate electrode from direct connection to power sources, preventing current leakage paths while maintaining the compensating effect for threshold voltage variation.
2Reliability
If additional transistors and capacitors are added to maintain uniform gate electrode voltage, then luminance uniformity is improved, but device complexity increases
Solution Approach 1:
The second transistor is designed to serve multiple functions: it stabilizes the gate electrode voltage, prevents current leakage to power sources, and works cooperatively with the capacitor to maintain voltage uniformity throughout the frame period. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity.
Solution Approach 2:
The capacitor is integrated into the existing pixel circuit structure by connecting it to the gate electrode node, merging the voltage stabilization function with the existing current control pathway. This integration approach allows the additional functionality to be added without creating completely separate circuit blocks, thus managing overall circuit complexity.
Data Source
AI summary
A pixel includes: an organic light emitting diode including a cathode electrode connected to a second power source; a first transistor including a first electrode connected to a first power source, and to control an amount of current flowing from the first power source to the second power source via the organic light emitting diode in response to a data signal; a plurality of second transistors connected in series between a gate electrode of the first transistor and an initialization power source, and to be turned on when a scan signal is supplied to an i−1-th (i is a natural number) scan line; and a first capacitor connected between a voltage source and a first node, the first node being between the plurality of second transistors.