Power Off Method for Display Devices with Oxide TFTs
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Solution Overview
Problem
Organic EL displays with oxide thin film transistors experience threshold voltage shifts due to electrical stress, leading to variations in current supply and degradation of display quality, even when powered off.
Innovation Solution
A power off method for display devices that involves detecting a power off operation and setting a voltage equivalent to the threshold voltage of the drive transistor in a capacitance element to suppress electrical stress, followed by immediate power supply cessation to the display panel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If power supply is stopped immediately without voltage adjustment, then power consumption is reduced, but threshold voltage shifts occur due to electrical stress on drive transistors
Solution Approach 1:
The patent applies preliminary action by adjusting the voltage to a specific level before cutting off power supply. The control unit sets the voltage to a predetermined value that minimizes electrical stress on drive transistors, then immediately stops power supply. This preliminary voltage adjustment prevents threshold voltage shifts that would otherwise occur during power-off periods.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the voltage parameter before power cutoff. The control unit changes the voltage from the normal operating level to a specific predetermined level that suppresses electrical stress effects, then terminates power supply. This parameter transformation resolves the contradiction between maintaining transistor stability and reducing power consumption.
2Reliability
If voltage is adjusted to suppress electrical stress, then transistor stability is improved, but additional control complexity is introduced
Solution Approach 1:
The patent applies self-service by having the control unit automatically perform the voltage adjustment and power cutoff sequence without user intervention. The system autonomously detects power-off requests, adjusts voltage to the predetermined level, and terminates power supply, thereby maintaining transistor stability through automated control rather than manual intervention.
Solution Approach 2:
The patent implements feedback mechanisms where the control unit monitors power-off requests and automatically responds by adjusting voltage levels and cutting power supply. This closed-loop control ensures that the voltage is set to the optimal predetermined value before power cutoff, maintaining transistor stability through automated feedback-based control.
3Speed
If power supply is stopped immediately, then response time is reduced, but display quality degrades due to threshold voltage shifts
Solution Approach 1:
The patent applies preliminary action by performing the voltage adjustment immediately upon detecting a power-off request, before the actual power cutoff occurs. This rapid preliminary voltage setting prevents threshold voltage shifts and maintains display quality, while the subsequent immediate power cutoff ensures fast response time.
Solution Approach 2:
The patent applies the skipping principle by rapidly executing the voltage adjustment and power cutoff sequence without unnecessary delays. The control unit quickly sets the voltage to the predetermined level and immediately terminates power supply, rushing through the power-off process to maintain both fast response time and display quality.
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 method effectively prevents threshold voltage shifts of drive transistors during power off, stabilizing the electric field and reducing variations among pixels, thereby enhancing display quality and longevity.
Implementation Method 1
a capacitance element that is connected to a gate of the drive transistor and holds a voltage representing the luminance
Implementation Method 2
a light emitting element that emits light with luminance corresponding to an amount of current supplied
Data Source
AI summary
A power off method of a display device includes: detecting a power off operation on the display device; setting, when the power off operation is detected, a voltage for suppressing electrical stress on a drive transistor, in a capacitance element in each of a plurality of pixel circuits; and stopping power supply to a display panel immediately after the voltage is set.