OLED Pixel Circuit On-Bias Stabilization
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Solution Overview
Problem
Existing pixel circuits for organic light emitting display devices face issues with unintended emission, over-current, and high power consumption due to hysteresis and step efficiency problems, particularly when driving transistors are on-biased.
Innovation Solution
A pixel circuit design that includes specific transistor configurations and signal phase delays to prevent unintended emission and reduce power consumption, featuring transistors connected to different scan and emission lines with phase-delayed signals to manage the on-bias state of driving transistors effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the driving transistor is allowed to be on-biased to solve hysteresis and step efficiency issues, then display quality is improved, but unintended emission and over-current occur
Solution Approach 1:
The pixel circuit applies initialization voltage to the anode electrode of the organic light emitting diode before the emission signal is activated. This preliminary action ensures that the anode electrode is properly initialized to prevent unintended emission when the driving transistor is on-biased, while still allowing accurate grayscale expression during normal operation.
Solution Approach 2:
The pixel circuit introduces a seventh transistor as an intermediary component to control the connection between the anode electrode and the initialization voltage line. This intermediary transistor is selectively activated to apply initialization voltage only when needed, preventing unintended emission while maintaining the on-biased state of the driving transistor for accurate grayscale expression.
2Speed
If the driving transistor is allowed to be on-biased to improve step efficiency, then response speed is improved, but power consumption increases
Solution Approach 1:
The pixel circuit applies initialization voltage periodically through the seventh transistor at specific timing (when the emission signal is activated), rather than continuously. This periodic action maintains the fast response capability of the on-biased driving transistor while reducing power consumption by limiting initialization current flow to only when necessary.
3Manufacturing precision
If the driving transistor is allowed to be on-biased to reduce hysteresis, then grayscale accuracy is improved, but over-current occurs during initialization
Solution Approach 1:
The pixel circuit applies initialization voltage to the anode electrode before the emission phase begins, ensuring that the organic light emitting diode is properly initialized without causing over-current during the on-biased operation of the driving transistor. The seventh transistor controls this preliminary initialization action to occur only when needed.
Solution Approach 2:
The seventh transistor serves as an intermediary that controls the flow of initialization voltage to the anode electrode, preventing over-current by selectively enabling this connection only during specific timing conditions when the emission signal is activated, while allowing the driving transistor to maintain its on-biased state for accurate grayscale expression.
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
The proposed pixel circuit effectively prevents unintended emission and reduces power consumption by stabilizing the on-bias state of driving transistors, ensuring accurate grayscale expression and minimizing current flow during initialization.
Implementation Method 1
An organic light emitting display device displays an image using an organic light emitting diode that generates light by recombination of electrons and holes
Data Source
AI summary
A pixel circuit includes: an organic light emitting diode (OLED); a first transistor having first and second electrodes and a first gate electrode; a second transistor connected between a data line and the first electrode, controlled by a first scan line; a third transistor connected between the second electrode and the a electrode of the first transistor, controlled by the first scan line; a fourth transistor connected between the first gate electrode and a first initialization voltage line, controlled by a second scan line; a fifth transistor connected between a power line and first electrode, controlled by a first emission line; a sixth transistor connected between the second electrode and the OLED and controlled by a second emission line; and a storage capacitor connected between the first gate electrode and the power line, wherein the first emission line and the second emission line are located at different nodes.