Computer graphics processing and selective visual display system – Display driving control circuitry
Reexamination Certificate
2000-12-28
2003-04-29
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Display driving control circuitry
C345S087000
Reexamination Certificate
active
06556192
ABSTRACT:
This application is based on Korean Patent Application No. 1999-26942, filed on Jul. 5, 1999, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a method and apparatus that prevents a white-screen error from occurring in the LCD device, and an LCD device incorporating the method and apparatus.
2. Discussion of the Related Art
LCD devices including display and drive portions are widely adopted as a display device for notebook computers or laptop computers because of a smaller size than conventional cathode ray tubes (CRTs). And recently, as the LCD devices become to display natural-like colors, desktop computers arc also adopting the LCD device as a display device. The LCD device has advantages of low power consumption, low electromagnetic radiation, and small size compared with a CRT.
Now, with reference to
FIG. 1
, a detailed explanation of the drive portion of an LCD device used for a desktop computer will be provided.
An interface
10
receives horizontal synchronous signals “HSYNC,” vertical synchronous signals “VSYNC,” and image data signals “DATA.” The interface
10
is electrically connected (hereinafter, connected) with an interface controller
12
and an LCD controller
14
, which is connected with a DC/DC converter
16
. In addition, the LCD controller
14
is connected with gate-line driving circuits
18
and data-line driving circuits
20
, while the gate-line driving circuits
18
and data-line driving circuits
20
are connected with gate lines and data lines of an LCD panel
22
. Though not shown in
FIG. 1
, the LCD panel
22
has a plurality of unit pixels arranged in a matrix shape, and each unit pixel has a thin film transistor (TFT). Gate and source electrodes of the TFTs are connected by means of the gate lines and data lines with the gate-line driving circuits
18
and the data-line driving circuits
20
, respectively.
From power source devices, or power supply circuits (not shown), a direct current (DC) supply voltage, for example, 3.3 VDC is applied to the DC/DC converter
16
and the LCD controller
14
. Therewith, the DC/DC converter
16
provides first, second, and third output power source voltages of −5, 16, and 8.7 VDC. Among the output power source voltages, the first and second output power source voltages −5 and 16 VDC are supplied for the gate-line driving circuits.
As the drive portion including the interface
10
et al. receives video signals from a video card of the desktop computer, the display portion including the LCD panel
22
displays images. The role and operation of each device shown in
FIG. 1
will be explained hereinafter.
When the video card transmits the video signals including HSYNC and VSYNC to the interface
10
, the interface
10
processes them such that images displayed by the LCD panel
22
coincide with preset resolution and optimum display size. Herein, the interface controller
12
transmits interface control signals to the interface
10
such that the interface
10
operates according to the interface control signals. As a result, the interface
10
produces data signals which are applied to the LCD controller
14
.
The LCD controller
14
transmits video data signals to the data-line driving circuits
20
according to some clock signals, and applies gate start signals and timing signals to the gate-line driving circuits
18
. At this point, the DC/DC converter
16
, which is supplied 3.3 VDC from the power source (not shown), provides a plurality of different DC voltage levels to the gate-line driving circuits
18
and the data-line driving circuits
20
, respectively.
The data-line driving circuits
20
and the gate-line driving circuits
18
transmit pixel data and gate signals to the LCD panel
22
, and the LCD panel
22
displays certain images from the pixel data signals according to the gate signals.
Hereinafter, a white screen error of the above-mentioned LCD device will be explained with reference to FIG.
2
.
As shown, the LCD device conventionally has a delay time between the output power source voltages, specifically the first and second output power source voltages that are applied to the gate-line driving circuits, and the data signals that are respectively applied by the DC/DC converter
16
and the interface
10
. That is to say, the output power source voltages begin to increase at a time period “T
1
” and reach their normal values at a subsequent time period “T
2
” while the data signals begin at a further subsequent time period “T
3
.” Therefore, the output power source voltages go ahead of the data signals by the time period “T
2
,” which is conventionally designed to be less than 20 ms inclusive. In other words, since there conventionally occurs an abnormal transient phase in the output power source voltages when the power source of the desktop computer is turned on or off, the output power source voltages should begin ahead of the data signals by a preset time period to assure a normal operation of the LCD device, namely, to exclude the abnormal state where the data signals are applied during the transient period “T
1
” of the output power source voltages.
However, when the delay time is too long, the output power source voltage is applied to the gate-line driving circuit too long without the display data signals being applied to the data-line driving circuit. In that abnormal case, an over-current is applied to the gate electrode of the TFT in the LCD panel such that a surge protector or breaker of the DC/DC converter powers down all of the output power source voltages. And as a result, while a back light is still illuminating, there exists no image data displayed on the LCD panel such that only a white color is shown to users, which is called as the white-screen error. The white screen error continues until the users turn off the main power for the desktop computer.
The above-mentioned problem causes users to distrust the overall product, such that repair service costs of venders are increased.
SUMMARY OF THE INVENTION
Accordingly, the principles of the present invention relate to a liquid crystal display device that is designed to substantially obviate one or more of the problems due to the limitations and disadvantages of the related art.
It is an object of the present invention to provide a method and apparatus for preventing the white-screen errors.
To achieve the above object, in one aspect the present invention provides A driving portion of a liquid crystal display device, comprising a data-line driving circuit; a gate-line driving circuit; an interface outputting data signals; a liquid crystal display controller receiving the data signals and outputting display data signals to the data-line driving circuit and timing signals to the gate-line driving circuit; a DC/DC converter supplying a plurality of output power source voltages to the gate-line driving circuit and the data-line driving circuit; a voltage detector detecting a voltage level of one of the output power source voltages supplied by the DC/DC converter and outputting a feedback signal; and an interface controller receiving the feedback signal from the voltage detector, outputting enable signals to the interface and to the DC/DC converter, and outputting a control signal to advance the data signals when the detected voltage level of the one output power source voltage is less than 90% of a preset voltage level.
Preferably, the voltage detector includes a transistor having gate, source and drain electrodes and being turned on and off according to the output power source voltage from the DC/DC converter.
Preferably, the transistor is a thin film transistor.
Also preferably, the voltage detector includes a first resistor electrically connecting the gate electrode of the transistor with an output terminal of the DC/DC converter and a second resistor electrically connecting the drain electrode of the transistor with the liquid crys
Hjerpe Richard
Laneau Ronald
LG. Philips LCD Co. Ltd.
McKenna Long & Aldridge LLP
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