Scanning Driver with Plural Turn-Off Voltages for OLED Displays
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Solution Overview
Problem
Amorphous silicon thin-film transistors in OLED displays experience threshold voltage shifts due to unidirectional voltage application, leading to non-uniform current flow and image degradation, with polysilicon TFTs being complex and costly to manufacture for large displays.
Innovation Solution
A display device and driving method that apply alternating normal data voltages and reverse bias voltages to data lines, with distinct turn-on and turn-off voltage levels, using a scanning driver with shift registers and level shifters to manage these voltages, ensuring each pixel receives voltages at different predetermined times to prevent threshold voltage degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous silicon TFTs are used in OLED displays, then manufacturing complexity and cost are reduced, but threshold voltage shifts occur due to unidirectional voltage application
Solution Approach 1:
The patent applies periodic reverse bias voltages to the data lines at predetermined intervals during the display operation. This periodic action resets the threshold voltage of the driving TFTs by inducing opposite polarity charges in the oxide layer, preventing cumulative threshold voltage shifts that would otherwise occur with continuous unidirectional voltage application. The reverse bias is applied in synchronization with the display refresh cycle, ensuring both manufacturing simplicity and long-term reliability.
2Reliability
If reverse bias voltage is applied to prevent threshold voltage degradation, then threshold voltage stability is improved, but leakage current increases due to switching transistor operation
Solution Approach 1:
The patent applies reverse bias voltage selectively to specific data lines based on their switching transistor's characteristics. The scanning driver identifies which data lines require threshold voltage reset and applies reverse bias only to those lines, rather than uniformly to all data lines. This localized approach minimizes the total leakage current while still preventing threshold voltage degradation in the affected transistors.
Solution Approach 2:
The system uses the existing switching transistor infrastructure to apply the reverse bias voltage. The scanning driver leverages the same transistor switching mechanism already present in the display architecture, turning the switching transistor into a self-serving component that both controls normal display operation and facilitates threshold voltage reset, thereby avoiding additional dedicated components that would increase leakage current.
3Reliability
If multiple voltage levels are used for scanning signals, then threshold voltage stabilization is achieved, but device complexity increases
Solution Approach 1:
The scanning driver is designed to perform multiple functions using the same hardware infrastructure. It simultaneously controls the timing of data voltage application, generates the reverse bias voltage sequences, and manages the synchronization between display refresh and threshold voltage reset operations. This multi-functional design avoids the need for separate dedicated circuits for each function, thereby achieving threshold voltage stabilization without proportionally increasing device complexity.
Data Source
AI summary
A display device includes a plurality of scanning lines, a plurality of data lines intersecting the scanning lines, a plurality of pixels each of which includes a switching transistor connected to a scanning line and a data line, a driving transistor connected to the switching transistor, and an emitting element connected to the driving transistor, wherein a data driver applies data voltages to the data line, and a scanning driver applies scanning signals each of which has at least three different voltage levels to the scanning line.