Organic EL Display Power-Off Voltage Stabilization
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Solution Overview
Problem
The shift in threshold voltage of driving transistors in organic EL displays due to electric stress during power-off periods affects the display quality by causing variations in current supply, leading to degradation in brightness control.
Innovation Solution
A method and apparatus that detect a power-off operation and set the capacitive elements of pixel circuits to a black-level voltage, immediately stopping power supply to the display panel, thereby suppressing electric stress on the driving transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If power is stopped immediately without setting black-level voltage, then power-off time is reduced and energy saving is improved, but threshold voltage shift occurs due to electric stress on driving transistors
Solution Approach 1:
The patent applies preliminary action by setting the black-level voltage to the capacitive elements before stopping power supply. This preparatory step ensures that driving transistors are in a stable state with minimal electric stress before power is cut off, preventing threshold voltage shift while enabling immediate power-off for energy saving.
Solution Approach 2:
The patent changes the voltage parameter from normal operation voltage to black-level voltage (0V or near 0V) before power-off. This parameter change eliminates electric stress on driving transistors by setting the gate voltage to a level that prevents charge accumulation, thereby maintaining threshold voltage stability during power-off period.
2Reliability
If black-level voltage is set before power-off, then threshold voltage stability is improved, but power-off sequence complexity increases
Solution Approach 1:
The patent merges the black-level voltage setting operation with the existing power-off control sequence. By integrating the voltage setting step into the standard power-off procedure, the system achieves threshold voltage stability without requiring a separate, complex power-off sequence. The control signal that sets black-level voltage is combined with the power-off control logic.
3Loss of time
If power is stopped immediately, then display refresh time is reduced, but display quality degrades due to threshold voltage shift
Solution Approach 1:
The patent applies preliminary action by pre-setting the black-level voltage to capacitive elements before cutting power. This ensures that when power is immediately stopped, the driving transistors maintain their threshold voltage characteristics, preventing display quality degradation while achieving fast power-off for reduced time loss.
Solution Approach 2:
The patent skips the intermediate step of gradual voltage reduction and directly transitions to black-level voltage before power-off. This rushing through the voltage transition ensures that threshold voltage shift is prevented without extending the power-off time, maintaining both display quality and fast power-off performance.
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 approach effectively prevents the shift in threshold voltage during power-off periods, maintaining display quality by ensuring consistent current supply and reducing image degradation.
Implementation Method 1
a capacitive element that is connected to the gate of the driving transistor and stores a brightness voltage
Implementation Method 2
a light-emitting element that emits light according to the amount of current supplied
Data Source
AI summary
A method for powering off a display apparatus includes: detecting a power-off operation input to a display apparatus; upon detection of the power-off operation, setting capacitive elements of a plurality of pixel circuits so as to have a black-level voltage; and stopping supply of power to a display panel immediately after the voltage is set.