Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-03-29
2003-10-14
Niebling, John F. (Department: 2812)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S143000, C349S141000, C349S140000, C349S139000, C349S042000
Reexamination Certificate
active
06633360
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an active matrix type liquid crystal display apparatus for use in a liquid crystal television set, a notebook personal computer, and the like.
FIGS. 24 and 25
are a plan view and a sectional view, respectively, of a conventional active matrix type liquid crystal display apparatus. The active matrix type liquid crystal display apparatus is constituted essentially of a liquid crystal panel
1
, a gate driver
2
, a source driver
3
, and a backlight
4
.
The liquid crystal panel
1
has an active matrix board
5
, an opposed board
6
, a liquid crystal layer
7
sandwiched between the active matrix board
5
and the opposed board
6
, and a polarizer (not shown) attached to the outer side of each of the active matrix board
5
and the opposed board
6
.
On an insulation substrate
5
a
of the active matrix board
5
, there are provided a plurality of scanning lines (not shown) disposed parallel with one another, a plurality of signal lines
9
parallel with one another and orthogonal to the scanning lines with an insulation film
8
disposed between the signal lines and the scanning lines, thin film transistors (TFTs)
10
disposed in the vicinity of intersections of the scanning lines and the signal lines
9
, and a plurality of pixel electrodes
11
disposed in regions surrounded with the scanning lines and the signal lines
9
.
FIG. 26
is a plan view showing a one-pixel part of the active matrix board
5
. Because the pixel electrode
11
and the signal line
9
are formed in the same layer, the pixel electrode
11
is spaced at a predetermined interval from the signal line
9
to prevent the pixel electrode
11
from contacting the signal line
9
. In the TFT
10
which is a three-terminal element, electrical continuity between a drain electrode
13
and a source electrode
14
is controlled by a voltage applied to a gate electrode
12
. The gate electrode
12
is connected to a scanning line
15
adjacent thereto. The source electrode
14
is connected to the signal line
9
adjacent thereto. The drain electrode
13
is connected to the pixel electrode
11
.
The opposed board
6
is provided with color filters
16
formed in the order of red, green, and blue at positions corresponding to each pixel electrode
11
. A black matrix
17
is formed between the adjacent color filters
16
and
16
. The black matrix
17
serves as a light shield film for preventing leak of light from the gap between the pixel electrode
11
and the scanning line
15
as well as the signal line
9
. An opposed electrode
18
made of a transparent conductive material is formed on a layer of the black matrix
17
and the color filters
16
. The gate driver
2
and the source driver
3
are connected to terminals of the scanning lines
15
and those of the signal lines
9
, respectively, disposed on the periphery of the liquid crystal panel
1
.
The method of driving the active matrix type liquid crystal display apparatus having the construction will be described below.
When writing to an array of pixels of an nth row, an ON-signal (electric potential Vgh at which the TFT
10
is turned on) is input to a scanning line
15
n
of the nth row from the gate driver
2
. At this time, an OFF-signal (electric potential Vgl at which the TFT
10
is turned off) is input to scanning lines other than the scanning line
15
n
. Thus, only the TFTs
10
of the nth row are turned on. On the other hand, source signals having voltages to be applied to the pixels (pixel electrodes
11
and liquid crystal layer
7
) of the nth row are supplied to each signal line
9
from the source driver
3
.
Upon completion of write for the array of the pixels of the nth row terminates, the OFF-signal is input to the scanning line
15
n
, whereas the ON-signal is input to the next scanning line
15
(n+1). All pixels are charged with voltages corresponding to data by repeating the operation. The transmissivity of the liquid crystal layer
7
disposed between the pixel electrode
11
and the opposed electrode
18
changes depending to a voltage applied across the pixel electrode
11
and the opposed electrode
18
, and light emitted from the backlight
4
is therefore adjusted. As a result, images are displayed on the active matrix type liquid crystal display apparatus.
There is proposed a construction in which pixel electrodes are provided on an interlaminar insulation film so that the pixel electrodes and the signal line are formed as different layers and that the pixel electrodes overlap the signal lines (disclosed in Japanese Patent Application Laid-Open No. 63-279228).
FIG. 27
is a sectional view showing a one-pixel part of an active matrix type liquid crystal display apparatus having the above-mentioned construction in which pixel electrodes overlap signal lines.
FIG. 28
is a plan view of an active matrix board
24
shown in FIG.
27
. In the construction, pixel electrodes
21
and signal lines
22
are formed as separate layers, and the pixel electrodes
21
are overlaid on the signal lines
22
through an interlaminar insulation film
23
. Thus, it is possible to eliminate the gaps between the pixel electrodes
21
and the adjacent signal lines
22
. Thus, it is possible to enlarge the area of the pixel electrodes
21
(aperture ratio) and thus reduce the power consumption of the active matrix type liquid crystal display apparatus. In
FIGS. 27 and 28
, reference numeral
24
a
denotes an insulation substrate,
25
denotes a TFT,
26
denotes a liquid crystal layer,
27
denotes an opposed electrode,
28
denotes an opposed board,
29
denotes a scanning line,
30
denotes a contact hole,
31
denotes an auxiliary capacitor electrode, and
32
denotes an auxiliary capacitor line.
However, in comparison with the construction shown in
FIG. 26
in which the pixel electrode
11
is spaced at a predetermined interval from the signal line
9
, the construction in which the pixel electrodes
21
overlap the signal lines
22
invites an increased capacitance Csd between the pixel electrode
21
and the signal line
22
. With the increase of the capacitance Csd, the source signal causes a pixel electric potential to change easily. Eventually, there will occur display characteristic deterioration called shadowing phenomenon.
The mechanism of the shadowing phenomenon will be described below by using an equivalent circuit of the active matrix board
24
shown in FIG.
29
. When a TFT
25
is turned on as a result of input of an ON-signal Vgh to a scanning line Gn, a pixel electrode P
1
is supplied with a voltage Vs
1
from a signal line S
1
.
Next, when the TFT
25
is turned off as a result of input of an OFF-signal Vgl to the scanning line Gn, a voltage Vs
1
′ corresponding to data to be written to a pixel electrode P
2
of a next stage is supplied to the signal line S
1
. At this time, the voltage of the pixel electrode P
1
is influenced by the voltage Vs
1
′ of the signal line S
1
through the capacitance Csd
1
. Supposing that the voltage of the pixel electrode P
1
at that time is Vp
1
, the voltage Vp
1
is expressed as follows:
Vp
11
=
Vs
1
−(
Csd
1
(
Vs
1
−Vs
1
′)+
Csd
2
(
Vs
2
−
Vs
2
′))/(
Cp+Csd
1
+
Csd
2
) (1)
where Cp is a capacitance of the pixel electrode (Cp=liquid crystal capacitance, Clc+auxiliary electrode capacitance, Ccs), Csd
1
is a capacitance between the signal line S
1
and the pixel electrode P
1
, Csd
2
is a capacitance between a signal line S
2
and the pixel electrode P
1
, Vs
1
and Vs
2
are voltages of the signal lines S
1
and S
2
, respectively, in the case where the scanning line Gn of an nth row is in an ON-state, and Vs
1
′ and Vs
2
′ are voltages of the signal lines S
1
and S
2
, respectively, in the case where a scanning line G(n+1) of an (n+1)th row is in an ON-state.
In a gate line inversion driving method (namely, “1H inversion driving”) which is a conventional method of driving the active matrix type liquid cryst
Ban Atsushi
Okada Yoshihiro
Kennedy Jennifer M.
Niebling John F.
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