OLED Driving Transistor Inversion Circuit for Threshold Voltage Shift
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional OLED displays using amorphous silicon TFTs suffer from threshold voltage shift due to unidirectional voltage application, leading to non-uniform current flow and reduced image quality and shortened OLED lifetime.
Innovation Solution
A display device with a light emitting element, first and second driving transistors, switching transistors, and inverters that alternately generate and apply inversion voltages to the driving transistors, along with capacitors to store and supply data and inversion voltages, to maintain uniform current flow and reduce threshold voltage shift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous silicon TFTs are used in OLED displays, then manufacturing complexity is reduced and large displays can be easily produced, but threshold voltage shifts occur over time due to unidirectional voltage application, degrading image quality and shortening device lifetime
Solution Approach 1:
The patent applies periodic action by alternately applying data voltage and inversion voltage to the driving TFTs in alternating frames. The inversion voltage is generated by inverters and applied during odd frames, while data voltage is applied during even frames, creating a periodic alternation that prevents cumulative threshold voltage shift and extends device lifetime while maintaining manufacturing simplicity
Solution Approach 2:
The patent uses inversion by generating an inversion voltage with opposite polarity to the data voltage and applying it to the driving TFTs during alternate frames. This inversion mechanism counteracts the unidirectional voltage stress that causes threshold voltage shift, thereby improving reliability without complicating the manufacturing process
2Device complexity
If unidirectional voltage is continuously applied to the TFT gate, then the circuit is simple, but current flow becomes non-uniform and image quality degrades over time
Solution Approach 1:
The patent implements periodic action by switching between data voltage and inversion voltage application in alternating frames. This periodic voltage alternation ensures uniform current flow through the OLED by preventing continuous unidirectional stress on the TFT, thereby maintaining image quality without significantly increasing circuit complexity
Solution Approach 2:
The patent changes the voltage parameter by introducing an inversion voltage with opposite polarity to the data voltage. This parameter change creates alternating voltage conditions that maintain current uniformity and prevent image degradation, achieving precise control over electrical parameters while keeping the overall circuit design manageable
3Reliability
If polysilicon TFTs are used, then device performance is improved, but manufacturing complexity increases and device size is limited
Solution Approach 1:
The patent changes the material parameter from polysilicon to amorphous silicon for the TFTs, enabling large-scale manufacturing while maintaining adequate device performance. Combined with the inversion voltage mechanism, this parameter change allows the system to achieve both manufacturing simplicity and sufficient reliability for large OLED displays
Data Source
AI summary
A display device including a plurality of pixels is provided, each pixel includes: a light emitting element; first and second driving transistors connected between a driving voltage and the light emitting element and supplying a driving current to the light emitting element; a first switching transistor transmitting a data voltage to the first driving transistor; a second switching transistor transmitting a data voltage to the second driving transistor; a first inverter generating an inversion voltage having a polarity opposite the data voltage and applying the inversion voltage to the first driving transistor; and a second inverter generating an inversion voltage having a polarity opposite the data voltage and applying the inversion voltage to the second driving transistor.