LCD TFT Gate and Backlight Timing for Threshold Voltage Recovery
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Solution Overview
Problem
Existing liquid crystal display devices using oxide semiconductors face negative shifts in threshold voltage due to stray light, which are not effectively addressed by prior art, and there is a need for a timely recovery mechanism.
Innovation Solution
A liquid crystal display device with a control unit that executes a writing process with a positive gate voltage, followed by a retention process with a negative gate voltage, and a specific process involving continuous positive gate voltage application with concurrent backlight illumination to recover the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a negative gate voltage is applied to the oxide semiconductor TFT to retain the image, then power consumption is reduced, but the threshold voltage undergoes a negative shift due to stray light
Solution Approach 1:
The patent applies a positive gate voltage before the negative gate voltage is applied. This preliminary positive voltage application prevents the harmful effect of stray light by establishing a positive potential in the oxide semiconductor layer beforehand, thereby avoiding the negative shift in threshold voltage when the negative gate voltage is subsequently applied for image retention.
Solution Approach 2:
The patent applies a positive gate voltage as a counter-action before the negative gate voltage is applied. This preliminary positive voltage application counteracts the potential harmful effect of stray light by establishing a positive potential in the oxide semiconductor layer beforehand, thereby preventing the negative shift in threshold voltage that would otherwise occur during negative voltage retention.
2Reliability
If the backlight device is driven at high luminance continuously, then the threshold voltage recovers effectively, but power consumption increases
Solution Approach 1:
The patent drives the backlight device periodically rather than continuously. The control unit drives the backlight device during specific periods when the positive gate voltage is applied, and turns it off during other periods. This periodic operation enables sufficient threshold voltage recovery while significantly reducing overall power consumption compared to continuous high-luminance operation.
Solution Approach 2:
The patent dynamically controls the backlight device operation based on the gate voltage application timing. The control unit adjusts the backlight device state (on/off) in sync with the gate voltage cycles, driving it only when needed for threshold recovery. This dynamic control optimizes the balance between recovery effectiveness and power consumption.
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 device effectively recovers the threshold voltage of TFTs subjected to negative shifts, reducing power consumption and avoiding user incongruity by adjusting backlight luminance based on device usage.
Implementation Method 1
The stray light causes an electron-hole pair to be generated in the oxide semiconductor
Implementation Method 2
applying a positive gate voltage to the oxide semiconductor TFT and subjecting the oxide semiconductor TFT to photoirradiation with the stray light causes the threshold voltage of the TFT to undergo a change in a plus direction
Data Source
AI summary
A liquid crystal display device includes a liquid crystal panel, a lighting device, and a control unit. The liquid crystal panel includes a TFT. The control unit executes a writing process of writing an image based on a video signal to the liquid crystal panel by applying a positive gate voltage to the TFT, a retention process of, in a state where a negative gate voltage is applied to the TFT, retaining the image written to the liquid crystal panel by the writing process, a specific process of, at a predetermined timing, continuously applying the positive gate voltage to the TFT and then finishing applying the positive gate voltage, and a specific turn-on driving process of, during execution of the specific process, driving the lighting device to glow at least in a predetermined period of time during which the positive gate voltage is continuously applied to the TFT.