Gate driving circuit in liquid crystal display

Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix

Reexamination Certificate

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Details

C345S099000, C345S100000, C345S087000, C345S211000, C345S213000

Reexamination Certificate

active

06414670

ABSTRACT:

This Application claims the benefit of Korean application no. 34290/1998 filed on Aug. 24, 1998, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a gate driving circuit in a liquid crystal display.
2. Background of the Related Art
Referring to
FIG. 1
a
, a liquid crystal display is, in general, provided with a liquid crystal panel
11
, a driver unit
12
having a plurality of gate line drivers (GD) around the liquid crystal panel
11
, and a source line driver unit
13
having a plurality of source line drivers (SD). As shown in
FIG. 1
b
, the liquid crystal panel
11
is provided with a plurality of gate lines G
1
, G
2
, G
3
, - - - , Gn, a plurality of source lines S
1
, S
2
, S
3
, - - - , Sn in a direction crossing each of the gate lines, a thin film transistor
11
a
formed at a crossing point of the gate lines and the source lines, and a liquid crystal capacitor
11
b
connected to its respective thin film transistor
11
a.
In order to display an image on the liquid crystal display, after applying a driving signal to the gate lines in a sequence, a data signal is applied to the source lines, causing a change of the orientation of liquid crystal stored in the respective liquid crystal stored in the respective liquid crystal capacitors, thus displaying an image on the liquid crystal panel
11
. The driving signal applied to the gate lines is provided from the gate line drivers GD. And, the data signal applied to the source lines is provided from the source line drivers SD. At least one gate line drivers GD and source line drivers SD are provided depending on the size of the liquid crystal panel.
FIG. 2
illustrates details of the gate line driver GD. The gate line driver GD includes a level changing unit
21
, a shift registering unit
22
, a level shifting unit
23
, and a buffering unit
24
. The level changing unit
21
changes a level V
DL
or V
DD
of an external signal into a level Vss or V
DD
required for the system operation. The shift registering unit
22
is provided with 154 shift registers SR
1
~SR
154
, each operative in response to a signal level changed by the level changing unit
21
, for shifting a driving signal applied to the gate line in a sequence. The level shifting unit
23
is provided with
154
level shifters LS
1
~LS
154
, each for shifting a level of the driving signal from the shift registering unit
22
to a level Vss or V
COM
.
The buffering unit
24
outputs signals out
1
~out
154
which are applied to the gate lines in a sequence. For example, initially when the first buffer BF
1
provides a high signal V
COM
, the remaining buffers provide a low signal V
L
. Then, the buffering unit
24
is shifted, so that in this time, the second buffer BF
2
provides a high signal, while the remaining buffers including the first buffer BF
1
provide a low signal. Thus, the high signal is applied starting from the first buffer BF
1
to the 154
th
buffer BF
154
in a sequence for applying the high signal starting from the first gate line to the 154
th
gate line in the liquid crystal panel
11
in sequence.
The number of the gate line driver GD changes according to the size of the liquid crystal panel
11
. For example, if four gate line drivers GD are provided, the number of the gate lines in the liquid crystal panel
11
will be 154×4=616.
As shown in
FIG. 2
, each of the gate line driver GD applies a signal from the buffering unit
24
to the gate line with either a high or low signal depending on received signals STV
1
, STV
2
, CPV, and OE. The STV
1
and the STV
2
signals are shift data input/output signals, i.e., bidirectional signals. When an arbitrary one of the plurality of gate drivers completes providing all the 154 signals in sequence, the next one comes into operation. The STV
1
signal is an operation signal provided to the forward gate line driver, and the STV
2
is an operation signal provided to the backward gate line driver. Accordingly, upon receiving the STV
1
signal, the arbitrary gate line driver provides the STV
2
signal to the next gate line driver after applying a driving signal to the gate line. The CPV signal is a vertical shift clock signal and the OE signal is an output enable signal.
FIG. 3
illustrates the operation waveform diagram of the gate line driver. Referring to
FIG. 3
, the STV
1
signal is provided at a first falling edge of the CPV signal (clock signal), shifted to the second shift register SR
2
through the first shift register SR
1
, and passed through the first level shifter LS
1
and the buffer BF
1
, to provide a high level out
1
signal to be applied to the first gate line at a second rising edge of the CPV signal. Then, the signal shifted to the second shift register SR
2
at the next falling edge of the CPV signal is shifted to the third shift register SR
3
, passed through the second level shifter LS
2
and the second buffer BF
2
, and provides a high level out
2
signal to the second gate line at a third rising edge of the CPV signal. Thus, out
1
to out 154 signals are provided in sequence matched to the rising edges of the clock signal clk according to the foregoing method. After providing the signals out
1
up to out
154
, the STV
2
, an operation signal for the next gate line driver, is provided. The STV
2
signal, being equivalent of the STV
1
signal for the next gate line driver, provides 154 signals in sequence as explained before.
FIG. 4
illustrates a conventional gate driver circuit. Referring to
FIG. 4
, the gate driver circuit is provided with a plurality of gate line drivers connected in series. A first gate line driver
41
-
1
is synchronous to a clock signal CPV and operative in response to a driving signal of the STV signal. The first gate line driver
41
-
1
provides a STV
2
signal to a second gate line driver
41
-
2
at a moment its own 154
th
signal is provided. Accordingly, the second gate line driver
41
-
2
provides signals out
1
to out
154
in succession as explained before. Then, the second gate line driver
41
-
2
provides a STV
2
signal to a third gate line driver
41
-
3
at a moment its own 154
th
signal is provided. Thus, the plurality of gate line drivers connected in series in the conventional gate driving circuit are driven in succession.
With reference to the waveforms shown in
FIG. 5
, if one of the plurality of gate lines in the liquid crystal panel
11
is selected (i.e., a high signal is applied), other gate lines are applied with low signals. A driving signal (i.e., the high signal) applied to one of the gate lines is shifted in succession synchronous to every rising edge of the clock signal. Of the signals provided from the first gate line driver
41
-
1
in
FIG. 4
, when the signal out
154
is provided, the STV
2
signal is provided synchronized to the falling edge of the clock signal. The STV
2
, equivalent of the STV
1
for the second gate line driver
41
-
2
, causes the second gate line driver
41
-
2
to provide signals from out
1
to out
154
in succession. When all the gate line drivers complete all operation in succession, one image is displayed on the liquid crystal panel.
However, the conventional gate line driver circuit has the following problems. In the gate line driver circuit provided with the plurality of gate line drivers, all of the gate line drivers are provided with the clock signals continuously started from the driving of the first gate line driver until the driving of the last gate line driver. Accordingly, the unnecessary driving of gate line drivers due to unnecessary application of the clock signal causes an wasteful power consumption.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a gate driving circuit in a liquid crystal display 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 a gate driving circuit in a liquid crystal display

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