Pixel Circuit Driving Method for Consistent Luminance
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Solution Overview
Problem
Existing light emitting devices face challenges in accurately controlling driving current variations across multiple gradations due to electrical characteristic variations in driving transistors, limiting effective compensation and resulting in inconsistent luminance.
Innovation Solution
A method is introduced that involves a pixel circuit with a light emitting element and a driving transistor connected in series, along with a storage capacitor between the light emitting element and the driving transistor, where a driving signal is supplied to the gate of the driving transistor with a controlled time rate of change, allowing the open circuit voltage of the storage capacitor to set the driving current independently of the transistor's threshold voltage or mobility, thereby maintaining consistent gradations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gate-source voltage is set to threshold voltage and then changed to voltage corresponding to gradation, then compensation for threshold voltage and mobility variations is achieved, but effective compensation is limited to specific gradations and variations cannot be corrected for other gradations
Solution Approach 1:
The patent changes the parameter of gate voltage application timing and method. Instead of setting gate-source voltage to threshold voltage and then changing to gradation voltage, the invention applies a voltage signal with a specific time rate of change (dV/dt) to the gate. This parameter change enables the compensation to work across multiple gradations by making the driving current dependent on the voltage change rate rather than absolute voltage levels, thereby resolving the limitation of being effective only for specific gradations
2Reliability
If conventional driving methods are used, then device complexity is reduced, but driving current variations cannot be suppressed across multiple gradations
Solution Approach 1:
The patent introduces dynamics by applying a voltage signal with a time rate of change rather than a static voltage level. The gate voltage is dynamically changed over time with a controlled dV/dt characteristic, which enables the driving transistor to operate in a regime where the current is determined by the voltage change rate. This dynamic approach suppresses driving current variations across gradations while maintaining relatively simple device structure
Solution Approach 2:
The patent employs periodic action through the time-varying voltage signal applied to the gate. By using a voltage signal that changes periodically or in a controlled temporal pattern (with specific rise and fall times), the system achieves consistent driving current across different gradations. The periodic nature of the voltage application allows the capacitor to charge and discharge in a controlled manner, ensuring reliability across multiple gradations
Data Source
AI summary
Provided is a method of driving a pixel circuit including a light emitting element and a driving transistor which are connected in series to each other, and a storage capacitor disposed between a path between the light emitting element and the driving transistor and a gate of the driving transistor, the method including the steps of: supplying a driving signal to a gate of the driving transistor; and changing the potential of the driving signal over time so that the time rate of change of the potential of the driving signal at the point in time when the supply of the driving signal stops becomes the time rate of change corresponding to a specified gradation of the pixel circuit.