Organic EL Pixel Circuit Discharge Method for Power-Off Reliability
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Solution Overview
Problem
The pixel circuit of organic EL display devices does not include a data compensation circuit to compensate for threshold voltage variations, leading to electric charge remaining in the circuit during power off, causing transistor deterioration and afterimage issues when power is turned back on.
Innovation Solution
A method for driving active-matrix display devices that includes a data compensation circuit and an initialization circuit to set the first node to a ground potential during power off, ensuring no electric charge remains by preventing the gate terminal of the drive transistor from being charged with a gate-to-source voltage, using a second ground potential that is either less than or greater than the first ground potential depending on the type of transistor, and utilizing an initialization line and writing transistor to maintain the drive transistor in an OFF state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional pixel circuit without data compensation circuit is used, then the device complexity is reduced, but electric charge remains in the pixel circuit during power off, causing transistor deterioration and afterimage issues
Solution Approach 1:
The patent applies preliminary action by performing initialization of the first node to ground potential during the OFF sequence before power is fully turned off. This preliminary discharge action ensures that no electric charge remains in the pixel circuit when power is removed, preventing transistor deterioration and afterimage formation while maintaining a relatively simple circuit structure.
2Ease of operation
If the first node is not initialized to ground potential during power off, then the initialization circuit operation is simplified, but electric charge remains in the pixel circuit causing afterimage and transistor deterioration
Solution Approach 1:
The patent implements preliminary action by initializing the first node to ground potential during the OFF sequence before power shutdown. This preliminary discharge operation prevents harmful electric charge retention in the pixel circuit, eliminating afterimage and transistor deterioration issues while maintaining straightforward initialization circuit operation.
3Reliability
If a ground potential is applied to the first node during OFF sequence, then electric charge is discharged from the pixel circuit, but the drive transistor may be incorrectly turned on if potentials are not properly controlled
Solution Approach 1:
The patent applies local quality by differentiating the ground potential application to different nodes. The first node is initialized to ground potential through the initialization circuit, while the second node receives ground potential through the data line during the OFF sequence. This localized potential control ensures proper discharge of the pixel circuit while preventing incorrect drive transistor activation through precise potential management.
Solution Approach 2:
The patent implements parameter changes by controlling the timing and potential levels applied to different nodes during the OFF sequence. By changing the potential parameters of the first and second nodes to appropriate ground levels at specific times, the patent ensures reliable pixel circuit discharge while maintaining drive transistor in the OFF state, avoiding incorrect activation.
4Reliability
If the data line supplies ground potential to the second node during OFF sequence, then the pixel circuit is discharged, but this requires precise coordination with scanning line activation
Solution Approach 1:
The patent applies merging by combining the discharge operations for the first and second nodes into a unified OFF sequence. The initialization of the first node to ground potential and the supply of ground potential to the second node through the data line are coordinated as integrated steps during the OFF sequence, ensuring complete pixel circuit discharge while managing control complexity through systematic coordination.
Data Source
AI summary
Provided are a display device drive method and a display device, both of which allow a pixel circuit to be discharged without leaving any electric charge in an OFF sequence for powering off the display device.During an OFF sequence period, a first node N1 is set to a first ground potential Vgnd1, which is a potential higher than an initialization potential Vini. As a result, even when a second ground potential Vgnd2 is supplied through a data line Dj to a second conductive terminal of a drive transistor T1, a gate terminal of the drive transistor T1 is not charged with a gate-to-source voltage Vgs. Therefore, an organic EL display device 1 is powered off with the gate terminal of the drive transistor T1 being charged with the first ground potential Vgnd1 leaving no electric charge in a pixel circuit 11 after the power off.