Driving circuit of a liquid crystal display device

Details Driving circuit of a liquid crystal display device Driving circuit of a liquid crystal display device

2001-12-28

2004-05-04

Chang, Kent (Department: 2673)

Computer graphics processing and selective visual display system

Plural physical display element control system

Display elements arranged in matrix

C345S094000, C345S098000

Reexamination Certificate

active

06731259

ABSTRACT:

This application claims the benefit of the Korean Application No. P2000-84114 filed on Dec. 28, 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 (LCD) device, and more particularly, to a driving circuit of a LCD device.
2. Discussion of the Related Art
Generally, an LCD device includes two glass substrates and a liquid crystal layer sealed between them. A thin film transistor (TFT)-LCD is used as a switching element that switches a signal voltage in the liquid crystal layer.
As shown in
FIG. 1
, the TFT-LCD includes a lower glass substrate
1
provided with a TFT as a switching element, an upper glass substrate
2
provided with a color filter, and a liquid crystal layer
3
injected between the two glass substrates
1
and
2
. The TFT-LCD is a non-light-emitting device that obtains an image effect based on the electro-optical characteristics of the liquid crystal layer.
The lower glass substrate
1
includes TFT arrays
4
. The upper glass substrate
2
includes a black matrix
5
, a color filter layer
6
, a common electrode
7
, and an alignment film
8
.
The lower glass substrate
1
and the upper glass substrate
2
are attached to each other by a sealant
9
such as epoxy resin. A driving circuit
11
on a printed circuit board (PCB)
10
is connected with the lower glass substrate
1
through a tape carrier package (TCP)
12
.
A module of the aforementioned LCD includes four elements. The four elements of the LCD module includes a LCD panel with a liquid crystal injected between two substrates, a driver for driving the LCD panel, a PCB provided with various circuit elements, and an external structure having a back light
13
.
A driving circuit of a related art LCD device will be described with reference to
FIG. 2
, which is a block diagram of a related art LCD device.
As shown in
FIG. 2
, the related art LCD device includes a LCD panel
21
, a gate driver
22
, a source driver
23
, a gamma voltage generator
24
, and a timing controller
25
. In the LCD panel
21
, a plurality of gate lines are arranged to cross a plurality of data lines. A TFT and a pixel electrode are arranged at each crossing portion of the gate and data lines. The gate driver
22
sequentially applies a driving signal to the gate lines. The source driver
23
applies a data signal to the data lines. The gamma voltage generator
24
applies a reference voltage to the source driver
23
. The timing controller
25
applies various control signals and voltages to the gate driver
22
and the source driver
23
.
In the aforementioned LCD device, light irradiated from a back light (not shown) passes through each of R (red), G (green), and B (blue) color filters in accordance with a voltage applied to each pixel electrode of the LCD panel
21
, thereby displaying picture images.
To maintain a stable display quality of the LCD device, an exact and uniform gamma voltage is required. The gamma voltage is generated by a resistance string having a plurality of serially arranged resistors. The gamma voltage is divided to adapt to the transmittivity characteristic of the liquid crystal panel and to obtain a required gray level.
FIG. 3
is a detailed schematic view of the gamma voltage generator of FIG.
2
.
The related art LCD device is based on a dot inversion method, in which digital data has 6 bits.
As shown in
FIG. 3
, the related art gamma voltage generator includes two voltage strings
33
and
35
arranged in parallel between a power source voltage terminal Vdd and a ground voltage terminal Vss, and an amplifier portion
37
.
The respective voltage strings
33
and
35
include a plurality of resistors R
1
-R
6
and R
7
-R
12
serially connected to generate a plurality of gamma voltages through voltage division by the respective resistors.
The plurality of gamma voltages generated by the respective voltage strings
33
and
35
are amplified by a corresponding amplifier of the amplifier portion
37
. Then the voltages are finally transmitted to the source driver
23
.
For example, as shown in
FIG. 3
, the first voltage string
33
includes six serially connected resistors that outputs five voltage sources V
1
-V
5
through voltage division by the respective resistors. The second voltage string
35
also includes six serially connected resistors that outputs five voltage sources V
6
-V
10
through voltage division by the respective resistors.
The voltage sources V
1
-V
10
are respectively transmitted to an input terminal at one side of a corresponding amplifier, where their noise is removed, and then output to the panel.
In the aforementioned gamma voltage generator, if a power source voltage Vdd is input, gamma voltages from V
1
to V
10
are set by serially connected resistance values. At this time, gray voltages of a positive frame are set as the voltages from V
1
to V
5
while gray voltages of a negative frame are set as the voltages from V
6
to V
10
.
Meanwhile, R, G, and B digital data input to the source driver
23
, as shown in a waveform of
FIG. 4
, are converted to analog-type voltage waveforms which will be applied to the LCD panel
21
. Then, the converted data are applied to each pixel electrode.
The source driver
23
will be described in more detail with reference to
FIG. 5
, which is a block diagram of the source driver.
As shown in
FIG. 5
, the source driver includes a shift register
51
, a sampling latch
52
, a holding latch
53
, a digital to analog (D/A) converter
54
, and an amplifier
55
.
The shift register
51
shifts a horizontal synchronizing signal through a source pulse clock HCLK and outputs a latch clock to the sampling latch
52
.
The sampling latch
52
samples the R, G, and B digital data for each column line (data line) in accordance with the latch clock output from the shift register
51
, and then latches the sampled R, G, and B data.
The holding latch
53
latches the R, G, and B data latched by the sampling latch
52
through a load signal LD.
The D/A converter
54
converts the R, G, and B digital data latched by the holding latch
53
to analog signals.
The amplifier
55
amplifies the R, G, and B data converted to analog signals at a certain width and outputs the amplified R, G, and B data to each data line of the LCD panel.
The source driver
23
samples and holds the R, G, and B digital data during 1 horizontal period, converts them to analog data, and amplifies the converted analog data at a certain width. If the holding latch
53
holds the R, G, and B data to be applied to nth data line, the sampling latch
52
samples the R, G, and B data to be applied to (n+1) data line.
The operation of the aforementioned related art driving circuit of the LCD device will be described below.
A video card (not shown) outputs R, G, and B digital data output to input to the source driver
23
without processing. The source driver
23
, controlled by the timing controller
25
, converts the R, G, and B digital data to analog signals that can be applied to the LCD panel
21
, and outputs the resultant values to each data line.
At this time, the gamma voltages obtained by voltage division through resistors are output from the gamma voltage generator
24
to the source driver
23
. The gamma voltages are varied depending on the LCD module.
If the gamma voltages are input to the source driver
23
, the same voltage is applied to each of R, G, and B pixel electrodes, and the liquid crystal is driven depending on the applied voltage to obtain corresponding brightness of light.
FIG. 6
shows a gray curve obtained by a fixed gamma voltage according to the related art, and
FIG. 7
shows a voltage type applied to the LCD panel
21
according to a gray scale by a reference voltage of a gamma voltage generator and a resistor string of the related art source driver
23
.
However, the related art driving circuit of the LCD device has several problems.
Among these problems, the related art luminance voltage characteristic does not adapt to variation of periphera

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