Electrostatic damage preventing apparatus for liquid crystal...

Details Electrostatic damage preventing apparatus for liquid crystal... Electrostatic damage preventing apparatus for liquid crystal...

2001-08-08

2004-02-10

Parker, Kenneth (Department: 2871)

Liquid crystal cells, elements and systems

Particular excitation of liquid crystal

Electrical excitation of liquid crystal

Reexamination Certificate

active

06690433

ABSTRACT:

The present invention claims the benefit of Korean Patent Application No. P2000-45942 filed in Korea on Aug. 8, 2000, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to an electrostatic damage preventing apparatus for a liquid crystal display.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls light transmissivity of liquid crystal cells in response to a video signal, thereby displaying an image. An active matrix LCD provided with a switching device for each liquid crystal cell is suitable for displaying moving images. A thin film transistor (TFT) is generally used as the switching device.
An active matrix LCD displays images corresponding to input video signals. Each pixel of the active matrix LCD includes a liquid crystal cell that controls the quantity of transmitted light according to a data signal voltage level input from the data line. A TFT is arranged at each intersection between gate lines and data lines. The data line will switch a data signal delivered to the liquid crystal cell in response to a scanning signal (i.e., a gate signal) from the gate line.
In an active matrix LCD as shown in
FIG. 1
, an electrostatic damage preventing apparatus, hereinafter referred briefly to as “ESD preventing apparatus,” for protecting a liquid crystal display panel from static electricity produced during the cutting of the substrate is provided at the liquid crystal display panel.
Referring to
FIG. 1
, the conventional ESD preventing apparatus includes a plurality of switching devices for ESD prevention that are provided on a TFT array
13
of a liquid crystal display panel
1
. The TFT array
13
has liquid crystal cells that respond to an electric field in order to control a quantity of transmitted light and thin film transistors (TFT's)
4
that respond to gate signals on gate lines
2
to selectively connect data lines
3
to liquid crystal cells
5
. The ends of the gate line
2
and the data line
3
are provided with pads
8
and
9
, respectively. The pad
8
provided at the end of the gate line
2
receives a gate signal from a gate driver (not shown) while the pad
9
provided at the end of the data line
4
receives a data signal from a data driver (not shown).
The ESD preventing apparatus further includes a ground voltage line
16
provided at an outer side of the liquid crystal display panel
1
, a horizontal ground voltage line
17
that extends from the ground voltage line
16
in parallel to the TFT array
13
, and a vertical ground voltage line
18
that is perpendicular to the TFT array
13
. A first ESD-preventing switching device
10
is connected between the ground voltage line
16
and the horizontal ground voltage line
17
, thereby preventing an electrostatic discharge voltage generated from pad
6
from being delivered into a fifth ESD-preventing switching device group
15
over the ground voltage line
16
.
A second ESD-preventing switching device group
14
has two parallel switching devices connected between the ground voltage line
16
and the vertical ground voltage line
18
, thereby diverting an electrostatic discharge voltage applied over the vertical ground voltage line
18
.
A third ESD-preventing switching device group
19
is connected between the gate line
2
and the vertical ground voltage line
18
, thereby diverting an electrostatic voltage by the second ESD-preventing switching device group
14
to prevent the electrostatic voltage from being directly applied to the TFT array
13
.
A fourth ESD-preventing switching device group
20
is connected between the gate pad
8
and the gate line
2
, thereby diverting an electrostatic voltage on the gate line
2
to prevent the electrostatic voltage from the gate pad
8
from being directly applied to the TFT array
13
.
A fifth ESD-preventing switching device group
15
is connected between the horizontal ground voltage line
17
and the TFT array
13
, thereby allowing a voltage on the horizontal ground voltage line
17
to be approximately equal to a voltage on the data line
3
.
A sixth ESD-preventing switching device group
22
is connected between a low gate voltage line
7
and the gate line
2
, thereby allowing a voltage on the gate line
2
to be diverted by the fourth ESD-preventing switching device group
20
to be approximately equal to a voltage on the low gate voltage line
7
.
A seventh ESD-preventing switching device group
21
is connected between a common voltage pad Vcom and the horizontal ground voltage line
17
, thereby diverting an electrostatic voltage applied via the common voltage pad Vcom.
In
FIG. 1
, the first to seventh ESD-preventing switching device groups
10
,
14
,
19
,
20
,
15
,
22
and
21
prevent damage to the TFT array
13
caused by an electrostatic voltage applied, via the ground voltage line
16
, to the gate line
2
or the data line
3
. Accordingly, the first ESD-preventing switching device
10
includes first and second TFT's
11
and
12
each having drain electrodes
11
a
and
12
a
and gate electrodes
11
b
and
12
b
respectively connected to each other. A source electrode
11
c
of the first TFT
11
and the drain electrode
12
a
of the second TFT
12
are connected to the horizontal ground voltage line
17
, and the drain electrode
11
a
of the first TFT
11
and a source electrode
12
c
of the second TFT
12
are connected to the horizontal voltage line
17
that is disposed perpendicular to the ground voltage line
16
.
Meanwhile, the second, third, fourth and sixth ESD-preventing switching devices
14
,
19
,
20
and
22
have similar configurations to provide the similar functions.
The conventional ESD preventing apparatus for the LCD has problematic in that, if excessive static electricity is supplied to the pad
6
, insulation breakage of the first ESD-preventing switching device
10
occurs. Similarly, if an excessive electrostatic voltage is applied to the seventh ESD-preventing switching device
21
that is connected in series between the common voltage pad Vcom and the horizontal ground voltage line
17
, insulation breakdown of the seventh ESD-preventing switching device
21
may occur. Accordingly, if the first and seventh ESD-preventing switching devices
10
and
21
undergo insulation breakage, then a large electrostatic voltage is applied to the TFT array
13
, thereby causing insulation breakage of the TFT
4
.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an electrostatic damage preventing apparatus that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an electrostatic damage preventing apparatus for a liquid crystal display that is capable of preventing insulation breakage or device damage through a single switching device connected in series to an external line of a thin film transistor array.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an electrostatic damage preventing apparatus for a thin film transistor array of a liquid crystal display includes a horizontal ground voltage line disposed at a first perimeter portion of the thin film array, a vertical ground voltage line disposed at a second perimeter portion of the thin film transistor array, and a first electrostatic damage-preventing switching device group including parallel connection of at least two electrostatic damage-preventing switching devices to divi

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