OLED Pixel Driving Circuit Stabilizing Node Potential to Prevent Flicker
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Solution Overview
Problem
Conventional pixel driving circuits for OLEDs face issues with non-uniform brightness, voltage jumps, and flicker due to threshold voltage variations and electric leakage in switching transistors, leading to inefficiencies and afterimages in organic light-emitting diodes.
Innovation Solution
A pixel driving circuit comprising a data writing unit, threshold compensation unit, driving unit, and voltage stabilizing unit, which includes transistors and capacitors to control and stabilize the potential at a connection node, preventing voltage changes and flicker by compensating for threshold voltage and stabilizing the node potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a switching transistor is used to transfer data voltage to the driving transistor, then the pixel driving circuit can be simplified and manufacturing can be easier, but electric leakage in the switching transistor causes gate voltage to vary and results in brightness flicker
Solution Approach 1:
A new switching transistor is introduced as an intermediary component between the data signal line and the gate of the driving transistor. This intermediary transistor controls the timing of data voltage application, ensuring that the gate voltage is only updated during the data writing phase and remains stable during the light emission phase, thereby preventing flicker caused by leakage in the original switching transistor.
Solution Approach 2:
The function of the single switching transistor is segmented into two distinct transistors: one dedicated to data writing and another dedicated to maintaining stable gate voltage during light emission. This segmentation allows each transistor to perform its specific function optimally, with the second transistor acting as a buffer to prevent leakage-induced voltage variations from affecting the driving transistor.
2Reliability
If threshold voltage compensation is implemented, then brightness non-uniformity can be reduced, but the circuit complexity increases with additional components
Solution Approach 1:
The threshold compensation function is merged with the existing switching transistor structure. The same switching transistor that controls data writing also participates in the threshold compensation process by controlling the charging of the storage capacitor during the compensation phase, thereby achieving threshold compensation without adding excessive circuit complexity.
Solution Approach 2:
The switching transistor is designed to perform multiple functions: data writing, threshold compensation, and maintaining gate voltage stability. By making the transistor universal and multi-functional, the need for separate dedicated components is reduced, balancing the trade-off between brightness uniformity and circuit complexity.
3Ease of operation
If the driving transistor converts data voltage to current for OLED, then the light emission can be controlled, but threshold voltage variations cause current instability and afterimages
Solution Approach 1:
The gate voltage is prepared and stabilized in advance during the data writing phase before the light emission phase begins. The switching transistor ensures that the gate voltage is fully established and stable before the OLED starts emitting light, preventing current instability and afterimages during the actual light emission process.
Solution Approach 2:
The circuit incorporates a feedback mechanism where the storage capacitor retains the gate voltage information and the switching transistor regulates its application to the driving transistor. This feedback loop ensures that the driving transistor receives a stable, compensated gate voltage that accounts for threshold voltage variations, thereby maintaining current stability.
Data Source
AI summary
The present invention provides a pixel driving circuit, a driving method thereof, and a display device. The pixel driving circuit of the present invention comprises a data writing unit, a threshold compensation unit, a driving unit, a light-emitting unit, and a voltage stabilizing unit; the data writing unit is connected with a first node, a scan signal line and a data signal line; the first node is a connection node between the data writing unit and the driving unit; the threshold compensation unit is connected with the first node, a first control signal line, a first voltage terminal and the driving unit; the driving unit is connected with the light-emitting unit; and the voltage stabilizing unit is connected with the data writing unit, a second control signal line and the first voltage terminal.