OLED Pixel Circuit with Dual Drain Transistor for Threshold Compensation
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Solution Overview
Problem
Organic light emitting displays face non-uniformity in display due to deviations in threshold voltages of driving transistors, which worsens at high resolution and high driving frequency, making it difficult to compensate for these deviations in time.
Innovation Solution
A pixel design that includes a driving transistor with first and second drain electrodes and a plurality of second transistors serially coupled between the first drain electrode and the gate electrode, along with a node electrically coupled to the second transistors and the second drain electrode, allowing for efficient compensation of threshold voltages through different current paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a compensating circuit is added to compensate for threshold voltage deviation, then threshold voltage compensation is improved, but device complexity increases
Solution Approach 1:
The patent merges the compensating circuit with the existing pixel circuit structure by integrating second transistors that share common components (gate electrode, source electrode, drain electrodes) with the driving transistor. This combination allows threshold voltage compensation functionality to be achieved without adding completely separate circuit blocks, thereby reducing the increase in device complexity while maintaining compensation reliability.
Solution Approach 2:
The second transistors in the patent serve multiple functions: they act as compensating elements for threshold voltage deviation, provide alternative current paths, and can function as part of the normal pixel circuit operation. This multi-functionality reduces the need for dedicated compensation-only components, effectively managing device complexity while achieving reliable threshold voltage compensation.
2Speed
If driving frequency is increased to improve response speed, then response speed is improved, but threshold voltage compensation time is reduced
Solution Approach 1:
The patent implements preliminary action by having the second transistors ready to provide compensating current paths from the beginning. When threshold voltage deviation occurs, the compensation can start immediately without waiting for a separate compensation phase, as the circuit structure is pre-configured to enable rapid compensation even at high driving frequencies.
Solution Approach 2:
The patent employs dynamic operation where the second transistors can be activated or deactivated based on real-time conditions. The circuit dynamically adjusts current flow through the second transistors to match the driving frequency requirements, allowing compensation to occur within the reduced time window at high frequencies by optimizing the timing and intensity of compensating current.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design stabilizes threshold voltage compensation, enabling uniform image display even at high resolution and high driving frequencies by managing current flow effectively through the second current path, reducing current deviation among transistors and maintaining image brightness.
Implementation Method 1
The organic light emitting displays display images using organic light emitting diodes (OLED) that generate light through re-combination of electrons and holes
Data Source
AI summary
A pixel capable of stably compensating for a threshold voltage is disclosed. The pixel includes an organic light emitting diode (OLED), a driving transistor having a gate electrode, a source electrode, and first and second drain electrodes. The pixel also has a plurality of second transistors serially coupled between the first drain electrode and a gate electrode of the driving transistor, and a node electrically coupled to the second drain electrode and to each of the second transistors.