Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
1998-06-11
2001-11-13
Lao, Lun-Yi (Department: 2673)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S095000, C345S092000
Reexamination Certificate
active
06317120
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus for driving a liquid crystal display (LCD) panel, and more particularly, to a voltage generating circuit for generating a plurality of voltage signals required to drive the LCD panel.
2. Description of the Conventional Art
A conventional LCD panel controls transmission of a light beam from a light source according to an input video signal to display a picture corresponding to the input video signal. The conventional LCD panel includes liquid crystal cells arranged in a matrix pattern and control switches for selectively activating the cells to receive the input video signals.
A driving apparatus is provided in the conventional LCD to actuate the control switches for activating the liquid crystal cells. The driving apparatus changes the polarity of video, voltage signals applied to the cells between a positive(+) and negative(−) polarity according to a set voltage level. This reduces the amount of driving voltage needed to drive the LCD panel and avoids degradation of liquid crystal. To change the polarity of video voltage signals, the driving apparatus must supply voltage signals for controlling the control switches and also a common voltage having a constant voltage level to each liquid crystal cell.
To generate the common voltage and the voltage signals for the control switches, a conventional LCD driving apparatus requires many different voltage generating circuits.
As shown in
FIG. 1
, the conventional LCD panel includes a plurality of thin film transistors (TFTs)
10
arranged at crossovers where gate lines
11
intersect data lines
13
, a plurality of liquid crystal cells
12
each connected between the source of a correspondence TFT
10
and the common voltage Vcom, a plurality of support capacitors
14
each connected in parallel with the corresponding liquid crystal cell
12
, a plurality of gate drivers
16
connected to the gate lines
11
, and a plurality of data line drivers
25
for supplying video signals to the data lines
13
. The LCD panel further includes a first pad
15
for inputting the common voltage Vcom, second pads
17
for inputting a gate floating voltage Vst, a third pad
19
for inputting a first gate driving voltage Vgh, and a fourth pad
21
for inputting a second gate driving voltage Vgl.
As shown in
FIG. 2
, each of the gate drivers
16
includes an NMOS transistor
18
and a PMOS transistor
20
for commonly receiving a gate control signal from a gate control line
23
. The NMOS transistor
18
transfers the first gate driving voltage Vgh from the third pad
19
to the gate line
11
when the gate control signal has a logical value of “1”. On the other hand, the PMOS transistor
20
transfers the second gate driving voltage Vgl from the fourth pad
21
to the gate line
11
when the gate control signal has a logical value of “0”.
To generate the common voltage Vcom, the gate floating voltage Vst and the first and second gate driving voltages Vgh and Vgl required by the LCD panel, the conventional LCD panel requires separate voltage generating circuits as shown in
FIGS. 3
to
5
. These voltage generating circuits included in the conventional LCD panel will be explained below referring to
FIGS. 3
to
5
.
First, the common voltage Vcom is commonly supplied, via the first pad
15
, to a number of liquid crystal cells
12
and support capacitors
14
. The gate floating voltage Vst is commonly supplied, via the second pads
17
, to the gate lines
11
. The common voltage Vcom and the gate floating voltage Vst are produced by a first voltage generating circuit as shown in FIG.
3
.
The first voltage generating circuit includes an operational amplifier A
1
for differentially amplifying a reference signal Vref and a horizontal synchronous signal Hsy, push-pull amplifiers Q
1
and Q
2
for further amplifying an output signal of the operational amplifier A
1
, and a resistor R
1
and capacitor Q
1
connected in parallel with each other for feeding back the output signal of the push-pull amplifiers Q
1
and Q
2
to be added to a line pulse LS. These push-pull amplifiers Q
1
and Q
2
generate the output signal of the operational amplifier A
1
by utilizing a high level supply voltage +Vcc and a low level supply voltage −Vcc. Each output signal of the push-pull amplifiers Q
1
and Q
2
is applied to the first pad
15
(
FIG. 1
) as a common voltage Vcom or to the second pad
17
as a gate floating voltage Vst. The voltage level of each output signal of the push-pull amplifiers Q
1
and Q
2
is determined by the voltage level of the reference voltage Vref.
Second, the first gate driving voltage Vgh is commonly supplied, via the third pad
19
, to the gate drivers
16
and is generated by a second voltage generating (or clamping) circuit as shown in FIG.
4
. The second voltage generating circuit includes a diode D
1
connected between the high level supply voltage source Vcc and the third pad
19
, and a capacitor C
2
connected between a line pulse (LS) input node HIN and the third pad
19
. The capacitor C
2
accumulates a difference between the voltage of line pulse LS and the high level supply voltage supplied through the diode D
1
from the high level voltage source Vcc. As a result, the first gate driving voltage Vgh changing in accordance with a logical value of the line pulse LS is generated and supplied to the third pad
19
.
Finally, the second gate driving voltage Vgl is commonly supplied, via the fourth pad
21
, to the gate drivers
16
and is generated by a third voltage generating (clamping) circuit as shown in FIG.
5
. The third voltage generating circuit includes a diode D
2
connected between a low level supply voltage source −Vcc and the fourth pad
21
, and a capacitor C
3
connected between the line pulse (LS) input node HIN and the fourth pad
21
. The capacitor C
3
accumulates a difference between the voltage of line pulse LS and the low level supply voltage applied through the diode D
2
from the low level voltage source −Vcc. The second gate driving voltage Vgl changing in accordance with a logical value of the line pulse LS is generated and supplied to the fourth pad
21
.
As described above, the conventional LCD panel driving apparatus requires at least several voltage generating circuits to generate all of the control voltage signals required to drive the LCD panel. This results in a complicated circuit configuration and more frequent circuit failures.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a voltage generating circuit for an LCD panel with a simplified circuit configuration, which is capable of generating a plurality of voltage signals necessary to drive the LCD panel.
It is another object of the present invention to provide a voltage generating circuit for an LCD panel which overcomes problems and disadvantages encountered in conventional LCD panels.
In order to attain these and other objects of the invention, a voltage generating circuit for a liquid crystal display panel according to the present invention includes a reference node, responsive to a line pulse having a logical value inverted every horizontal scanning interval, and having a voltage level varying according to the logical value of the line pulse; at least two reference voltage sources for generating voltage signals having different voltage levels; and at least two clamping means, coupled to the reference node, the reference voltage sources and the output nodes, for clamping at least two voltage signals from the reference voltage sources with a voltage of the line pulse, and for generating at least two control voltage signals to drive the liquid crystal display panel.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only,
Lao Lun-Yi
LG Electronics Inc.
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