Pixel Driving Circuit Ground Voltage Control for OLED Stress Reduction
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Solution Overview
Problem
Organic electro luminescence display devices face issues with stress on driving transistors and ghosting due to uncontrolled voltage application, particularly during black signal display and continuous positive voltage usage, leading to reduced lifespan and brightness deterioration.
Innovation Solution
The introduction of a ground terminal voltage controlling unit that sets different reference voltages for the data and emitting units, allowing for the application of negative voltage to the driving transistor and rapid discharge of storage capacitors, thereby reducing stress and preventing ghosting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If continuous positive voltage is applied to the driving transistor, then the device can operate continuously, but the stress on the driving transistor increases and lifespan decreases
Solution Approach 1:
The patent applies periodic voltage polarity reversal to the driving transistor. During normal operation, positive voltage is applied, but periodically the voltage polarity is reversed to negative. This periodic action allows the transistor to rest and recover from stress accumulated during continuous positive voltage operation, thereby extending lifespan while maintaining operational continuity.
2Device complexity
If only positive voltage is applied to the driving transistor, then the circuit operation is simplified, but threshold voltage shifts and brightness deteriorates
Solution Approach 1:
The patent implements periodic polarity reversal of the voltage applied to the driving transistor. By alternating between positive and negative voltage, the threshold voltage shift caused by continuous positive voltage is compensated. This maintains brightness stability without significantly increasing circuit complexity, as the reversal mechanism can be integrated into the existing driving circuitry.
3Device complexity
If the storage capacitor is not discharged, then the circuit operation is simplified, but ghosting occurs and device performance deteriorates
Solution Approach 1:
The patent utilizes periodic polarity reversal to achieve capacitor discharge. During the negative voltage phase, the storage capacitor discharges through the transistor, providing a simple yet effective mechanism to prevent ghosting without requiring additional discharge circuits or increasing operational complexity.
Data Source
AI summary
An organic electro luminance display device according to the present invention comprises a plurality of gate lines and data lines to define a plurality of pixels and a plurality of power lines to apply a signal to the pixels; a data driving unit for supplying the signal to the data line; an emitting unit at each pixel to emit; a first thin film transistor at each pixel, the first thin film transistor being turned on by the signal inputted through the gate line; a second thin film transistor at each pixel, the second thin film transistor being turned on to apply the signal to the emitting signal through the power line when the first thin film transistor is turned on; a ground terminal voltage controlling unit for controlling a first ground terminal voltage and a second ground terminal voltage to determine respectively the voltage output from the data driving unit and the voltage applied to the emitting unit according to the first ground terminal voltage and the second ground terminal voltage, wherein the second ground terminal voltage is higher than the first ground terminal voltage to apply the voltage lower than a reference voltage to the second thin film transistor.