EM Signal Control Circuit for OLED Stability
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Solution Overview
Problem
Conventional EM signal control circuits in organic light emitting display devices face issues with floating output nodes and voltage level changes due to transistor threshold voltage changes, leading to unreliable EM signal output during EM duty drive operations.
Innovation Solution
Incorporating additional transistors and capacitors to separate set and gate signals, and setting voltage levels of emission and gate power sources differently to maintain stable transistor turn-off and prevent voltage level changes, ensuring reliable EM signal output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional EM signal control circuit is used, then device complexity is low, but output node floats and EM signal reliability deteriorates during EM duty drive
Solution Approach 1:
The patent divides the control circuit into separate modules: a first control module for controlling the first transistor and a second control module for controlling the second transistor. This segmentation allows independent optimization of each control path, preventing the floating issue while managing complexity through modular design. The segmentation enables the circuit to maintain reliable EM signal output by ensuring at least one transistor remains conductive through dedicated control signals.
Solution Approach 2:
The patent introduces a capacitor as an intermediary element connected to the output node. This capacitor acts as a mediator that maintains voltage stability at the output node during transitions, preventing the floating phenomenon. The capacitor stores charge and provides a discharge path, ensuring the output node remains at a defined voltage level even when transistors switch states, thereby improving EM signal reliability without significantly increasing circuit complexity.
2Reliability
If transistor threshold voltage changes occur, then device manufacturing variation increases, but EM signal voltage level stability deteriorates
Solution Approach 1:
The patent employs dynamic control signals that adapt to transistor threshold voltage variations. The control signals are designed to adjust their voltage levels and timing based on the actual transistor states, ensuring that at least one transistor remains conductive despite manufacturing variations. This dynamic approach compensates for threshold voltage changes, maintaining stable EM signal voltage levels without requiring high manufacturing precision.
Solution Approach 2:
The patent changes the voltage parameters of control signals to compensate for transistor threshold voltage variations. By adjusting the voltage levels of control signals applied to the gates of transistors, the circuit ensures proper switching behavior despite manufacturing variations. This parameter adjustment strategy maintains EM signal stability by ensuring transistors switch at the correct moments regardless of threshold voltage differences caused by manufacturing tolerances.
3Reliability
If additional transistors and capacitors are added, then EM signal reliability improves, but device complexity increases
Solution Approach 1:
The patent designs the control circuit where additional components serve multiple functions. The capacitor, for example, simultaneously prevents output node floating, stabilizes voltage levels, and provides timing reference for transistor switching. The additional transistors are integrated into existing control paths, serving both as switching elements and as part of the control logic. This multi-functionality approach improves EM signal reliability while minimizing the increase in overall device complexity.
Solution Approach 2:
The patent merges the additional control components with the existing circuit architecture. The control signals for the first and second transistors are generated using shared control logic and power sources where possible. The capacitor is integrated into the existing output stage, combining its stabilizing function with the existing transistor switching mechanism. This merging approach reduces the overall complexity increase by avoiding completely separate additional circuits.
Data Source
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AI summary
Various embodiments relate to an EM signal control circuit, an EM signal control method, and an organic light emitting display device. The EM signal control circuit according to an embodiment includes additional elements (e.g., a transistor and a capacitor) configured to separate a set signal from a gate electrode of a transistor coupled to an output node and to stably keep turn-off of a transistor coupled to the output node. Voltage levels of a first emission power source and a first gate power source may be set differently from each other. Therefore, despite of a threshold voltage change of a transistor coupled to an output node, the transistor may remain turned off stably, thereby improving the reliability of the EM signal.