U.S. patent number RE44,314 [Application Number 12/814,805] was granted by the patent office on 2013-06-25 for liquid crystal display device.
This patent grant is currently assigned to Hitachi Displays, Ltd., Panasonic Liquid Crystal Display Co., Ltd.. The grantee listed for this patent is Yasuyuki Mishima, Shunsuke Morishita. Invention is credited to Yasuyuki Mishima, Shunsuke Morishita.
United States Patent |
RE44,314 |
Mishima , et al. |
June 25, 2013 |
Liquid crystal display device
Abstract
In spite of an increase in the size of a liquid crystal display
panel, it is possible to prevent the defective connection of a
flexible wiring board to a transparent substrate of the liquid
crystal display panel. A liquid crystal display device includes a
pair of transparent substrates arranged to oppose each other across
a liquid crystal, for which they are utilized to form a chamber, a
plurality of pixels formed along a spreading direction of the
liquid crystal, driving circuits for supplying video signals to the
pixels, and a flexible wiring board for supplying signals to the
input sides of the driving circuits from a substrate on which a
control circuit is mounted, the flexible wiring board being divided
into a plurality of portions.
Inventors: |
Mishima; Yasuyuki (Mobara,
JP), Morishita; Shunsuke (Mobari, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Mishima; Yasuyuki
Morishita; Shunsuke |
Mobara
Mobari |
N/A
N/A |
JP
JP |
|
|
Assignee: |
Hitachi Displays, Ltd. (Chiba,
JP)
Panasonic Liquid Crystal Display Co., Ltd. (Hyogo-ken,
JP)
|
Family
ID: |
18357519 |
Appl.
No.: |
12/814,805 |
Filed: |
June 14, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
12185317 |
Aug 4, 2008 |
Re. 41378 |
|
|
|
11165554 |
Jun 24, 2005 |
Re. 40706 |
|
|
Reissue of: |
09452462 |
Dec 2, 1999 |
6583844 |
Jun 24, 2003 |
|
|
Foreign Application Priority Data
|
|
|
|
|
Dec 2, 1998 [JP] |
|
|
10-342916 |
|
Current U.S.
Class: |
349/149; 349/150;
349/152; 349/151 |
Current CPC
Class: |
G02F
1/13452 (20130101) |
Current International
Class: |
G02F
1/1345 (20060101) |
Field of
Search: |
;349/149,150,151,152
;345/103 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Glick; Edward
Assistant Examiner: Chung; David
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus, LLP.
Parent Case Text
.Iadd.CROSS REFERENCE TO RELATED APPLICATIONS.Iaddend.
.Iadd.This is a continuation reissue of continuation reissue
application U.S. Ser. No. 12/185,317, filed Aug. 4, 2008, now U.S.
Pat. No. Re. 41,378, which is a continuation reissue of reissue
application U.S. Ser. No. 11/165,554, filed Jun. 24, 2005, now U.S.
Pat. No. Re. 40,706, which is a reissue of U.S. Pat. No. 6,583,844,
issued Jun. 24, 2003, the subject matter of which is incorporated
by reference herein..Iaddend.
Claims
What is claimed is:
.[.1. A liquid crystal display device, comprising: a liquid crystal
display panel having, a pair of substrates arranged to oppose each
other, a liquid crystal layer interposed between the pair of
substrates, a plurality of pixels being formed along the liquid
crystal layer; a plurality of driving circuits for supplying
signals to the pixels and being juxtaposed along one of edges of
the liquid crystal display panel, the plurality of driving circuits
being arranged adjacent one another and divided into a plurality of
driving circuits groups having plural driving circuits along the
one of the edges of the liquid crystal panel; a printed circuit
board having a control circuit mounted thereon which controls the
plurality of driving circuits; and a plurality of flexible wiring
boards being juxtaposed along a direction in which the plurality of
driving circuits are juxtaposed, a respective one of the plurality
of flexible wiring boards being provided for a respective one of
the plurality of driving circuits groups, each of the plurality of
flexible wiring boards having a connecting portion to be connected
to the printed circuit board and protruded portions provided in
correspondence with respective driving circuits of a respective
driving circuits group, the protruded portions being spaced from
one another and protruding toward the one of the edges of the
liquid crystal display panel and having respective ends mounted on
one of the pair of substrates at the one of the edges of the liquid
crystal display panel, wherein each of the plurality of flexible
wiring boards receives a control signal from the control circuit
through the connecting portion thereof and inputs the control
signal sequentially to respective input sides of the respective
driving circuits of the respective one of the driving circuit
groups corresponding thereto, and each of the protruded portions
thereof having at least one signal path thereof inputting the
control signal to the input side of the driving circuits of the
respective one of the driving circuits groups..].
.[.2. A liquid crystal display device according to claim 1, wherein
the plurality of driving circuits are ICs..].
.[.3. A liquid crystal display device according to claim 1, wherein
the control signal is an enable signal sent from the control
circuit to the plurality of driving circuits successively along the
one of the edges of the liquid crystal panel through each of the
plurality of flexible wiring boards and controls video signal
acquisition by the respective driving circuits performed
sequentially along the one of the edges of the liquid crystal
panel..].
.[.4. A liquid crystal display device according to claim 1, wherein
the printed circuit board is constructed to sequentially supply the
control signal from said control circuit between said flexible
wiring boards which are arranged adjacent to one another..].
.[.5. A liquid crystal display device according to claim 1, wherein
a pair of the connecting terminals of a pair of the plurality of
flexible wiring boards are arranged at respective sides of the pair
of the plurality of flexible wiring boards which are adjacent to
one another..].
.[.6. A liquid crystal display device according to claim 5, wherein
the control circuit confronts a region between the pair of the
connecting terminals of the pair of the plurality of flexible
wiring boards..].
.[.7. A liquid crystal display device according to claim 1, wherein
the control signal being supplied to the driving circuits
corresponding to the one of the plurality of flexible wiring boards
is a starting signal, and controls video signal acquisition of each
of the driving circuits corresponding thereto sequentially along
the one of the edges of the liquid crystal display panel as
transferred between the respective driving circuits corresponding
thereto..].
.[.8. A liquid crystal display device according to claim 1, wherein
at least one of the plurality of flexible wiring boards has another
connecting portion outputting the control signal outputted from one
of the driving circuits corresponding thereto..].
.[.9. A liquid crystal display device according to claim 1, wherein
each of the plurality of the pixels has a switching element, and
the plurality of driving circuits are mounted on the one of the
pair of substrates over which a plurality of video signal lines
being connected to at least one of the switching elements are
formed..].
.[.10. A liquid crystal display device according to claim 9,
wherein the plurality of video signal lines are divided into groups
in accordance with the driving circuits groups, and each of the
groups includes a plurality of video signal lines adjacent to each
other..].
.[.11. A liquid crystal display device, comprising: a liquid
crystal display panel having, a pair of substrates arranged to
oppose each other, a liquid crystal layer interposed between the
pair of substrates, a plurality of pixels being formed along the
liquid crystal layer; a plurality of driving circuits for supplying
signals to the pixels and being juxtaposed along one of edges of
the liquid crystal display panel, the plurality of driving circuits
being arranged adjacent one another and divided into a plurality of
driving circuits groups having plural driving circuits along the
one of the edges of the liquid crystal panel; a printed circuit
board having a control circuit mounted thereon which controls the
plurality of driving circuits; and a flexible wiring board, which
is arranged to extend along a direction in which the plurality of
driving circuits are juxtaposed, consisting of a plurality of
sections thereof provided in correspondence with the driving
circuits groups and arranged in an extension direction thereof,
each of the sections having a connecting portion to be connected to
the printed circuit board, and having protruded portions thereof
protruded toward the one of the edges of the liquid crystal display
panel in correspondence with the respective driving circuits
belonging to the one of the driving circuit groups and having
respective ends mounted on one of the pair of substrates at the one
of the edges of the liquid crystal display panel, the protruded
portions being spaced from each other at the ends thereof, wherein
a flexible wiring board receives a control signal from the control
circuit through one of the connecting portions of the sections
thereof, each of the protruded portions corresponds to one of the
driving circuits has at least one signal path for the control
signal to be connected to an input side of the driving circuit
corresponding thereto, each region of the flexible wiring board
between each pair of the sections which are adjacent to one another
along the extension direction thereof is narrower than the rest
thereof, and the control signal is inputted to each of the
plurality of driving circuits sequentially along the one of the
edges of the liquid crystal display panel and is transferred
through each region between the sections of the flexible wiring
board..].
.[.12. A liquid crystal display device according to claim 11,
wherein the flexible wiring board has multi-layered regions in the
respective section thereof where a plurality of the conductive
layers are stacked on each other, and the protruded portions and
the each region between the sections are thinner than the
multi-layered regions..].
.[.13. A liquid crystal display device according to claim 1,
wherein the flexible wiring board has a multi-layered region where
a plurality of the conductive layers being stacked on each other,
and the protruded portions thereof are thinner than the
multi-layered regions..].
.[.14. A liquid crystal display device according to claim 1,
wherein the plurality of flexible wiring boards consists of a pair
of flexible wiring boards extended and juxtaposed along the one of
the edges of the liquid crystal display panel..].
.[.15. A liquid crystal display device according to claim 11,
wherein the flexible wiring board comprises a plurality of flexible
wiring boards juxtaposed along the one of the edges of the liquid
crystal display panel for the respective section thereof, and a
pair of the plurality of flexible wiring boards adjacent to one
another are connected by a joint member provided at the region
therebetween..].
.[.16. A liquid crystal display device according to claim 11,
wherein the plurality of driving circuits are divided into a pair
of driving circuits groups each including a plurality of driving
circuits adjacent to each other along the one of the edges of the
liquid crystal display panel, and the flexible wiring board
consists of a pair of the sections thereof provided in
correspondence with the pair of driving circuits groups,
respectively..].
.Iadd.17. A display device comprising: a first substrate comprising
video signal lines for supplying a video signal to pixels, and
scanning signal lines for supplying a scanning signal to the
pixels; a first board comprising a control circuit; a plurality of
driving circuits comprising a plurality of first driving circuits
and a plurality of second driving circuits, each of the first and
second driving circuits supplying the video signal to the video
signal lines; a plurality of scanning signal line driving circuits
supplying the scanning signal to the scanning signal line; a second
board for supplying an output from the control circuit to the
plurality of first driving circuits, the second board being
arranged between the first substrate and the first board; a third
board for supplying an output from the control circuit to the
plurality of second driving circuits, the third board being
arranged between the first substrate and the first board; wherein
each pixel comprises a pixel electrode and a thin film transistor
for controlling application of the video signal to the pixel
electrode by the scanning signal; wherein the output from the
control circuit is supplied from a first area on the first board to
a third area on the second board; wherein the output from the
control circuit is supplied from a second area on the first board
to a fourth area on the third board; wherein the third area is
arranged adjacent one side of the second board, and the one side of
the second board is arranged adjacent to the third board; wherein
the fourth area is arranged adjacent one side of the third board,
and the one side of the third board is arranged adjacent to the
second board; wherein the first area on the first board overlaps
with the third area on the second board; wherein the second area on
the first board overlaps with the fourth area on the third board;
wherein the output from the control circuit to the plurality of the
first driving circuits is supplied through the second board
independently of the third board; wherein the output from the
control circuit to the plurality of the second driving circuits is
supplied through the third board independently of the second board;
and wherein the output from the control circuit to the plurality of
the scanning signal line driving circuits is supplied through the
first board..Iaddend.
.Iadd.18. A display device according to claim 17, wherein the first
substrate includes long sides and short sides, and wherein the
second board and the third board are arranged between one of the
long sides of the first substrate and the first board..Iaddend.
.Iadd.19. A display device according to claim 17, further
comprising a second substrate; wherein the second substrate and the
first substrate sandwich the liquid crystal layer; and wherein a
transparent electrode is arranged on the inside of the second
substrate..Iaddend.
.Iadd.20. A display device according to claim 18, further
comprising a second substrate; wherein the second substrate and the
first substrate sandwich the liquid crystal layer; and wherein a
transparent electrode is arranged on the inside of the second
substrate..Iaddend.
.Iadd.21. A display device comprising: a first substrate comprising
video signal lines for supplying the video signal for pixels, and
scanning signal lines for supplying a scanning signal for pixels; a
first board comprising a control circuit; a plurality of driving
circuits comprising a plurality of left driving circuits and a
plurality of right driving circuits, each of left and right driving
circuits being arranged horizontally, each of the driving circuits
supplying the video signal to the video signal lines; a plurality
of scanning signal line driving circuits supplying the scanning
signal to the scanning signal lines; a second board for supplying
an output from the control circuit to the plurality of left driving
circuits, the second board being arranged between the first
substrate and the first board; a third board for supplying an
output from the control circuit to the plurality of right driving
circuits, the third board being arranged between the first
substrate and the first board; wherein each pixel comprises a pixel
electrode, and a thin film transistor for controlling application
of the video image signal to the pixel electrode by the scanning
signal; wherein the output from the control circuit is supplied
from a first area on the first board to a third area on the second
board; wherein the output from the control circuit is supplied from
a second area on the first board to a fourth area on the third
board; wherein the third area is arranged adjacent one side of the
second board, and the one side of the second board is arranged
adjacent to the third board; wherein the fourth area is arranged
adjacent one side of the third board, the one side of the third
board is arranged adjacent to the second board; wherein the first
area on the first board overlaps with the third area on the second
board; wherein the second area on the first board overlaps with to
the fourth area on the third board; wherein the output from the
control circuit to the plurality of left driving circuits is
supplied through the second board independently of the third board;
wherein the output from the control circuit to the plurality of
right driving circuits is supplied through the third board
independent of the second board; wherein the control circuit is
arranged to overlap with the first area and the second area on the
first board; and wherein the output from the control circuit to the
plurality of the scanning signal line driving circuits is supplied
through the first board..Iaddend.
.Iadd.22. A display device according to claim 21, wherein the first
substrate includes long sides and short sides, and wherein the
second board and the third board are arranged between one of the
long sides of the first substrate and the first board..Iaddend.
.Iadd.23. A display device according to claim 21, further
comprising a second substrate; wherein the second substrate and the
first substrate sandwich the liquid crystal layer; and wherein a
transparent electrode is arranged on an inside of the second
substrate..Iaddend.
.Iadd.24. A display device according to claim 22, further
comprising a second substrate; wherein the second substrate and the
first substrate sandwich the liquid crystal layer; and wherein a
transparent electrode is arranged on the inside of the second
substrate..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device
and, more particularly, to an active matrix type of liquid crystal
display device.
2. Description of the Related Art
An active matrix type of liquid crystal display device is
characterized by a structure in which a switching element made of,
for example, a thin-film transistor (TFT) is incorporated in each
pixel of its liquid crystal display panel.
The active matrix type of liquid crystal display device has, as a
chamber for a liquid crystal, a pair of substrates (at least one of
which is a so-called transparent substrate having a sufficient
optical transmissivity) which are arranged to oppose each other
across the liquid crystal, and a pixel group is formed in a
direction in which the liquid crystal is spread along the main
surface of this substrate. This pixel group includes pixels each of
which is provided in a portion surrounded by two adjacent ones of a
plurality of scanning signal lines formed over the main surface of
one of the pair of substrates which faces the liquid crystal (a
liquid crystal layer) and by two adjacent ones of a plurality of
video signal lines formed to cross the plurality of scanning signal
lines. Each of the pixels is provided with a switching element to
be driven by a scanning signal supplied from one of the two
adjacent scanning signal lines and a pixel electrode to which a
video signal supplied from one of the two adjacent video signal
lines via this switching element is to be applied.
In this structure, a signal from a scanning driving circuit is
inputted from one end of each of the scanning signal lines, while a
signal from a video signal driving circuit is inputted from one end
of each of the video signal lines. These driving circuits are
mounted on the periphery of one of the substrates (the transparent
substrate).
Each of the driving circuits is arranged to receive an input signal
from a control circuit or the like which is mounted on, for
example, a printed circuit board, but in this case, the
transmission of signals to the driving circuits is effected by a
flexible wiring board connected between the printed circuit board
and one of the substrates of the liquid crystal display panel (for
example, the transparent substrate on which the driving circuits
are mounted).
The aforementioned flexible wiring board (also called "the flexible
printed circuit board", or "FPC" as its abbreviation) being
utilized for the liquid crystal display device is disclosed in e.g.
the Japanese Patent Laid-Open Nos. 270814/1995, 123489/1998,
38430/1999, and 52409/1999.
SUMMARY OF THE INVENTION
However, in a trend toward an increase in the size of the liquid
crystal display device constructed in the above-described manner,
it has been pointed out that a defective connection occasionally
occurs between the flexible wiring board and one transparent
substrate of the liquid crystal display panel.
In the above-described liquid crystal display device, one of the
pair of substrates (for example, the transparent substrate) and the
flexible wiring board are constructed so that each of
interconnecting terminals formed on the substrate and the
corresponding one of interconnecting terminals formed on the
flexible wiring board are opposed and connected to each other. It
has been found out that if the flexible wiring board is thermally
expanded, the positions of the interconnecting terminals formed on
the flexible wiring board deviate from those of the corresponding
interconnecting terminals formed on the transparent substrate.
Measures against this deviation have become indispensable because
the deviation becomes larger in proportion to-an increase in the
size of the liquid crystal display device (to be exact, the liquid
crystal display panel).
It has also been found out that the harmful effect of thermal
expansion of the flexible wiring board occurs not only while the
flexible wiring board is being connected to one of the transparent
substrates of the liquid crystal display panel, but also after the
flexible wiring board has been connected.
This is because even after the flexible wiring board has been
correctly connected, the connecting portions of the flexible wiring
board may peel due to an expansion of the flexible wiring
board.
Moreover, in the trend toward an increase in the size of the liquid
crystal display device constructed in the above-described manner,
it has been pointed out that a waveform distortion easily occurs in
a video signal which is transmitted through a video signal line or
lines located on one side in the direction of juxtaposition of
video signal lines among a plurality of video signal lines
juxtaposed over the main surface of the substrate.
In the case of a structure in which signals are supplied from the
control circuit to the respective driving circuits via the flexible
wiring board, it has been found out that a video signal transmitted
to a video signal line which is distant from the control circuit
suffers a distortion in its signal waveform during the process of
transmission by the influence of another connected driving
circuit.
The present invention has been made in view of the above-described
problems, and an object of the present invention is to provide a
liquid crystal display device which is suitable for preventing the
defective connection of a flexible wiring board to a transparent
substrate of a liquid crystal display panel in spite of an increase
in the size of the liquid crystal display panel.
Another object of the present invention is to provide a liquid
crystal display device which is suitable for preventing, in spite
of an increase in the size of the liquid crystal display panel, the
waveform distortion of a signal transmitted to a signal line which
is located on one side of the liquid crystal display panel in the
direction of juxtaposition of signal lines, among a plurality of
signal lines juxtaposed on the main surface of the substrate.
Representative features of the invention disclosed in the present
application will be described below in brief.
<Means 1>
A liquid crystal display device comprises: a liquid crystal display
panel having a liquid crystal (a liquid crystal layer), a pair of
substrates (at least one of which is a so-called transparent
substrate) arranged to oppose each other across the liquid crystal
to constitute a chamber for the liquid crystal, and a plurality of
pixels arranged along a spreading direction of the liquid crystal;
driving circuits juxtaposed on the liquid crystal display panel
(one of the pair of substrates), for supplying video signals or
scanning signals to the plurality of pixels; and a flexible wiring
board extended along a direction in which the plurality of driving
circuits are juxtaposed, for supplying signals to input sides of
the plurality of driving circuits, respectively, from a control
circuit (which is mounted on, for example, a printed circuit board
such as a control circuit board), wherein a structure for relaxing
thermal expansion is adopted in a portion of the flexible wiring
board on a side thereof connected to the driving circuits with
respect to the extension direction of the flexible wiring board.
This structure need not necessarily be applied to a portion which
is located on the opposite side to the aforesaid portion with
respect to the extension direction. One specific example of this
structure is that the flexible wiring board is:divided into
plurality along the extension direction.
In the liquid crystal display device constructed in this manner,
because the length of the flexible wiring board (for example, the
overall longitudinal length) is shorter than that in a conventional
structure, even if the flexible wiring board is thermally expanded,
it is possible to reduce thermal stress which occurs in the
connecting portions between the flexible wiring board and the
driving circuits.
Accordingly, in spite of an increase in the size of the liquid
crystal display panel, it is possible to prevent the defective
connection of the flexible wiring board to the transparent
substrate of the liquid crystal display panel.
<Means 2>
In the liquid crystal display device of the above-described means
1, the control circuit is characterized by being constructed so
that a signal is supplied from the control circuit to each of the
flexible wiring boards.
In accordance with the liquid crystal display device constructed in
this manner, the distances from the connecting portion of each of
the flexible wiring boards to the most distant signal line and to
the neighboring signal line or lines are shorter than those in the
conventional structure, whereby it is possible to prevent
occurrence of the waveform distortion of signals to be supplied to
the signal lines. The capacity of the interconnecting lines of the
flexible wiring board are increased by the driving circuits in
which circuits which repeat charging and discharging are
incorporated, but such capacity can be decreased to a great extent
because the number of the driving circuits 6 can be reduced to half
by using the above-described structure.
Accordingly, in spite of an increase in the size of the liquid
crystal display panel, it is possible to prevent waveform
distortion from occurring in a signal on a signal line which lies
on one side of the liquid crystal display panel in the direction of
juxtaposition of the signal lines.
These and other objects, features and advantages of the present
invention will become more apparent from the following description
when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view showing the entire structure of one
embodiment of a liquid crystal display device according to the
present invention;
FIG. 2 is a plan view showing the structure of another embodiment
of the drain circuit board of the liquid crystal display device
according to the present invention;
FIG. 3 is a plan view showing one embodiment of a pixel of the
liquid crystal display device according to the present
invention;
FIGS. 4A and 4B are views showing the structure of one embodiment
of a gate driving circuit and the peripheral portion thereof in the
liquid crystal display device according to the present invention,
FIG. 4A shows the plan-view arrangement thereof and FIG. 4B shows a
cross-sectional structure thereof respectively;
FIG. 5 is an explanatory view showing the relationship between the
input and output signals of the gate driving circuit in the liquid
crystal display device according to the present invention;
FIGS. 6A and 6B are views showing the structure of one embodiment
of a drain driving circuit and the peripheral portion thereof in
the liquid crystal display device according to the present
invention, FIG. 6A shows the plan-view arrangement thereof and FIG.
6B shows a cross-sectional structure thereof respectively;
FIG. 7 is an explanatory view showing the relationship between the
input and output signals of the drain driving circuit in the liquid
crystal display device according to the present invention;
FIG. 8 is a cross-sectional view showing the structure of a
flexible wiring board used in the liquid crystal display device
according to the present invention;
FIG. 9 is an explanatory view showing another embodiment of the
liquid crystal display device according to the present
invention;
FIG. 10A is an explanatory view showing one of the structural
features of the liquid crystal display device according to the
present invention in contrast to one of the conventional structures
being shown in FIG. 10B; and
FIGS. 11A, 11B, and 11C are plan views showing the variations of
the flexible wiring boards according to the present invention being
utilized for the printed drain circuit board of the liquid crystal
display device.
DETAILED DESCRIPTION
Embodiments of a liquid crystal display device according to the
present invention will be described below with reference to the
accompanying drawings.
Embodiment 1
<Entire Structure>
FIG. 1 is a schematic view showing, the structure of the entire
liquid crystal display device according to the present
invention.
In this embodiment, the present invention is applied to a liquid
crystal display device which adopts a so-called lateral electric
field type (also called an In-Plane-Switching type or IPS type)
known as a type having a wide viewing angle.
In FIG. 1, a liquid crystal display panel 1 is constructed as a
chamber for a liquid crystal (not shown) which has transparent
substrates 1A and 1B arranged to oppose each other across the
liquid crystal. In this case, one of the transparent substrate (the
lower substrate shown in FIG. 1: the matrix substrate 1A) is formed
to be slightly larger than the other transparent substrate (the
upper substrate shown in FIG. 1: the color filter substrate 1B),
and, as viewed in FIG. 1, the bottom and right edges of the
transparent substrate 1A are nearly flush with the bottom and right
edges of the transparent substrate 1B, respectively.
Accordingly, as viewed in FIG. 1, the left and top peripheries of
the transparent substrate 1A are formed to be extended outward from
the left and top peripheries of the transparent substrate 1B,
respectively. As will be described later in detail, this extended
portion is an area in which gate driving circuits and drain driving
circuits are mounted.
A plurality of pixels 2 are arranged in a two-dimensional (matrix)
form in the area of the transparent substrate (matrix substrate) 1A
which overlaps the transparent substrate (color filter substrate)
1B. Each of the pixels 2 is formed in an area surrounded by
scanning signal lines 3 which are formed to be extended in an x
direction as viewed in FIG. 1 and to be juxtaposed in a y direction
as viewed in FIG. 1 and video signal lines 4 which are formed to be
extended in the y direction and to be juxtaposed in the x
direction. Each of the pixels 2 is at least provided with a
switching element TFT to be driven by the supply of a scanning
signal from one of the video signal lines 3, and a pixel electrode
to which a video signal is to be applied, the video signal being
supplied from one of the video signal lines 4 via the switching
element TFT.
As described above, since the present embodiment adopts the
so-called lateral electric field type, each of the pixels 2 is
provided with a reference electrode and an added capacitive element
in addition to the above-described switching element TFT and pixel
electrode, as will be described later in detail.
Each of the scanning signal lines 3 is formed over the-transparent
substrate 1A in such a manner that one end of the same (the left
end as viewed in FIG. 1) is extended outward from the overlapping
area of the transparent substrate 1A which overlaps the transparent
substrate 1B, and the scanning signal line 3 is connected at this
one end to the output terminal of the corresponding one of gate
driving circuits (ICs) 5 which are mounted on the transparent
substrate 1A.
The scanning signal lines 3 are divided into groups each including
adjacent scanning signal lines, for the respective gate driving
circuits 5 provided on the transparent substrate 1A, and each of
these groups of the scanning signal lines 3 is connected to the
closest one of the plurality of gate driving circuits 5.
The structure of this portion will be described later in detail
with reference to. FIG. 4.
Similarly to the scanning signal lines 3, each of the video signal
lines 4 is formed over the transparent substrate 1A in such a
manner that one end of the same (the top end as viewed in FIG. 1)
is extended outward from the overlapping area of the transparent
substrate 1A which overlaps the transparent substrate 1B, and the
video signal line 4 is connected at this one end to the output
terminal of the corresponding one of drain driving circuits (ICs) 6
which are mounted on the transparent substrate 1A.
The video signal lines 4 are divided into groups, each including
adjacent scanning signal lines, for the respective plurality of
drain driving circuits 6 provided on the transparent substrate 1A,
and each of these groups of the video signal lines 4 is connected
to the closest one of the plurality of drain driving circuits
6.
The structure of this portion will be described later in detail
with reference to FIG. 6.
A printed circuit board 10 (a control circuit board 10) is arranged
in proximity to the liquid crystal display panel 1 provided with
the gate driving circuits 5 and the drain driving circuits 6 in the
above-described manner, and a control circuit 12 for supplying
input signals to the gate driving circuits 5 and the drain driving
circuits 6 are mounted on the printed circuit board 10 in addition
to a source circuit 11 and the like.
Signals from this control circuit 12 are supplied to the gate
driving circuits 5 and to the drain driving circuits 6 through
flexible wiring boards (a gate circuit board 15, a drain circuit
board 16A and a drain circuit board 16B).
The matrix substrate 1A on which the gate driving circuits 5 are
mounted is provided with signal input terminals for the respective
gate driving circuits 5. One of the flexible wiring boards (the
gate circuit board 15) has terminals which respectively correspond
to the signal input terminals for the gate driving circuits 5, and
is mounted on the periphery of the matrix substrate 1A (the left
end thereof as viewed in FIG. 1) so that these terminals are made
to correspond to the signal input terminals for the gate driving
circuits 5, respectively.
A portion of the gate circuit board 15 is formed to be extended to
the control board 10, and is connected at the extended portion to
the control board 10 via a connecting portion 18.
Output signals from the control circuit 12 mounted on the control
board 10 are inputted to the respective gate driving circuits 5
through interconnecting layers on the control board 10, the
connecting portion 18 and interconnecting layers on the gate
circuit board 15.
The matrix substrate 1A on which the drain driving circuits 6 are
mounted is provided with signal input terminals for the respective
drain driving circuits 6. Each of the other flexible wiring boards
(the drain circuit boards 16A and 16B) has terminals which
respectively correspond to the signal input terminals for the drain
driving circuits 6, and is mounted on the periphery of the matrix
substrate 1A (the top end thereof as viewed in FIG. 1) so that
these terminals are made to correspond to the signal input
terminals for the drain driving circuits 6, respectively.
A portion of each of the drain circuit boards 16A and 16B is formed
to be extended to the control board 10, and is connected at the
extended portion to the control board 10 via the corresponding one
of connecting portions 19A and 19B.
Output signals from the control circuit 12 mounted on the control
board 10 are inputted to the respective drain driving circuits 16A,
16B through interconnecting layers on the control board 10, the
connecting portions 19A and 19B and interconnecting layers on the
drain circuit boards 16A and 16B.
One feature of this embodiment resides in a structure in which the
drain circuit boards 16A and 16B mounted on the periphery of the
matrix substrate 1A on the side of the drain driving circuits 6 are
provided as two separate parts as shown in FIG. 1.
The reason why this structure is adopted is to prevent harmful
effects caused by thermal expansion due to an increase in the x
direction of FIG. 1 in the length of either of the drain circuit
boards which accompanies an increase in the size of the liquid
crystal display panel 1.
If either of the drain circuit boards 16A and 16B is thermally
expanded before the drain circuit boards 16A and 16B are connected
to the liquid crystal display panel 1, it is impossible to provide
satisfactory electrical connection between this expanded drain
circuit board and the liquid crystal display panel 1. This problem
occurs when interconnecting terminals are arranged on each of the
drain circuit boards 16A and 16B and the liquid crystal display
panel 1 (the main surface of the matrix substrate 1A), with the
interconnecting terminals of the drain circuit boards 16A and 16B
opposed to those of the liquid crystal display panel 1, and the
drain circuit boards 16A and 16B are mounted on the liquid crystal
display panel 1 so that these interconnecting terminals are
connected. Stated in more detail, the interconnecting terminals of
each of the drain circuit boards 16A and 16B and those of the
liquid crystal display panel 1 (a pair of an interconnecting
terminal of either of the drain circuit boards and an
interconnecting terminal of the liquid crystal display panel 1) are
connected via conductive bodies, respectively. Therefore, if a
large thermal expansion occurs in the drain circuit boards
(compared to the substrate 1A), the positions of the
interconnecting terminals to be connected to each other are
deviated from each other.
Even if a satisfactory electrical connection is realized without
the above-described harmful effects, there is a possibility that,
after the drain circuit boards 16A and 16B are connected to the
liquid crystal display panel 1, stress occurs between the connected
interconnecting terminals owing to a subsequent thermal expansion
of the drain circuit boards and a disconnection occurs between the
same.
For this reason, in this embodiment, by dividing a flexible wiring
board into two parts which are the drain circuit boards 16A and
16B, the thermal expansion of each of the drain circuit boards 16A
and 16B is restrained to relax the above-described harmful
effects.
Needless to say, the number of the divided flexible wiring boards
need not necessarily be limited to two. If the number of the
divided flexible wiring boards is greater than two, the effect on
the above-described harmful effect becomes far larger.
In addition, each of the drain circuit boards may be provided with
means for making the thermal expansion smaller on a side thereof
which is connected to the driving circuits, than on at least the
opposite side (for example, the side of each of the drain circuit
boards which is connected to the control board 10).
For example, as shown in FIG. 2, on the side of a drain circuit
board connected to the driving circuits, a slit 20 may be formed in
the drain circuit board in a direction perpendicular to the
longitudinal direction of the same.
In this case, although the drain circuit board is not divided as in
the case of the above-described embodiment, it is possible to
obtain an effect similar to that obtained in the case of the
divided drain circuit boards.
In the present embodiment, the connecting portions 19A and 19B for
the control board 10 are formed on the respective drain circuit
boards 16A and 16B which are, for example, two divided drain
circuit boards, and the mechanical and electrical connections
between the drain circuit boards 16A and 16B and the control board
10 are provided by the connecting portions 19A and 19B.
It is apparent from FIGS. 1 and 2 that both of the drain circuit
boards utilize flexible wiring boards (called flexible printed
circuit boards, also) having a plurality of protruding portions
(downwards in FIG. 10B) formed in accordance with a plurality of
the drain driving circuits. Advantages of this structural feature
will be explained with reference to FIGS. 10A and 10B.
One of the conventional liquid crystal display devices utilizes a
plurality of flexible printed circuit board 26A through 26E shown
in FIG. 10B, each of which corresponds to one of the drain driving
circuits 6. Each of the flexible wiring boards 26A through 26E has
at least a pair of alignment marks 261 (cross-shaped marks in FIG.
10B) for positioning a portion thereof on the matrix substrates.
The matrix substrates has similar alignment marks (not shown) to
those of the flexible wiring board in the vicinity of the terminals
thereof (not shown) to be connected to the leads 262 of the
flexible wiring board. When the flexible wiring boards are mounted
on the periphery of the matrix substrate 1A, both positions of the
respective flexible wiring board and the matrix substrate 1A are
adjusted in accordance with an optical observation of both pairs of
the alignment marks. As the definition of the liquid crystal
display panel becomes higher, the interval between the video signal
lines 4 adjacent to one another becomes finer, and so does the
interval between the scanning signal lines 3 adjacent to one
another. However, the width of each of the flexible wiring boards
26A through 26E is so limited geometrically that the pair of
alignment marks 261 makes an interval x.sub.L, of the leads 262
narrower, even if an interval x.sub.IC of the driving circuits 6
remains at the conventional value. As the interval x.sub.L becomes
narrower, the interval between the terminals formed at a periphery
of the matrix substrate 1A cannot but become narrower.
Consequently, the process for positioning the flexible wiring board
on the periphery of the matrix substrates becomes more difficult,
and the positioning accuracy is easily affected by the thermal
expansion of the flexible wiring board.
On the other hand, before mounting the flexible wiring boards 26A
through 26E on the printed circuit board 10 comprising the control
circuit 12 etc. after mounting them on the matrix substrate 1A,
there are some possibilities that the flexible wiring boards are
deformed slightly after a heat-treatment for fixing the leads
thereof 262 onto the terminals on the matrix substrate 1A. As FIG.
10B shows, each of the flexible wiring boards 26A through 26E has
one of the connecting parts 29A through 29E thereat, respectively.
Thus, such aforementioned deformations thereof will applies stress
to the connecting part thereof and makes positioning the connecting
parts thereof onto the printed circuit board difficult, even if the
deformations around the leads 262 thereof appears slightly.
With respect to these problems according to the conventional liquid
crystal display device having a structure shown in FIG. 10B, the
liquid crystal display device according to the present invention
utilizing the flexible wiring board 16A shown as FIG. 10A ensures
the interval x.sub.L of the leads 162 broader enough and eliminates
the aforementioned thermal deformation thereof. In the flexible
wiring board 16A, the leads 162 to be connected to the terminals
(not shown) on the matrix substrate 1A are formed on the respective
protruding portions thereof corresponding to the drain driving
circuits 6, respectively. As the protruding portions are combined
with each other at one of the sides thereof (at upper sides
thereof, in FIG. 10A), those protruding portions may be mounted on
the matrix substrate 1A together. Therefore, a pair of alignment
marks 161 need not to be formed at each of the protruding portions,
because the respective leads 162 of the five protruding portions
can be positioned onto the terminals of the matrix substrate 16A
together with each other by monitoring at least a pair of alignment
marks 161. As numbers of the alignment marks to be formed at
protruding portions, the broader areas thereof are obtained for the
respective leads 162. Consequently both the interval x.sub.L of the
leads 162 and the interval between the terminals to be connected
thereto can remains broader, even if the interval x.sub.IC of the
drain driving circuits 6 becomes narrower.
In the liquid crystal display device according to the present
invention, the flexible wiring board is divided to two or more
along one of the sides of the liquid crystal display panel.
Moreover, each of the two or more flexible wiring boards has a
plurality of protruding portions which are separated from each
other per one of the drain driving circuits 6 corresponding
thereto. These two structural features provide effects mutually to
reduce the thermal expansions appearing locally inside the flexible
wiring board inside. Therefore, each of the thermal expansions at
the respective protruding portion (around the leads 161) of the
flexible wiring board 16A is so reduced that any stress does not
affect the connecting portion 19A thereof.
The other structural feature of the liquid crystal display device
according to the present invention is to separate the flexible
wiring board 16A from the printed circuit board 10 carrying
electronic components and/or electric components, like the source
circuit 11 (the electric power supply, the electric power
regulator, or else) and the control circuit 12 (e.g. the timing
converter) shown in FIG. 1. If these components are mounted on the
flexible wiring board 16A, heat treatment has to be applied to the
flexible wiring board to fix the components thereon. In comparison
with the heat treatment for connecting the leads 162 of the
flexible wiring board to the terminals on the matrix substrate 1A,
the aforementioned heat treatment for electronic/electric
components is applied locally so as to fix the components more
rigidly on to the flexible wiring board. Therefore, the flexible
wiring board loses its flexibility which absorbs the aforementioned
stress due to the heat treatment other than that for fixing the
components. If the components are fixed to the flexible wiring
board before mounting it onto the matrix substrate 1A, the thermal
expansion at the aforementioned protruding portion can hardly be
reduced, and thus the leads thereof will deviate from the
respective terminals corresponding to the leads. If the components
are fixed to the flexible wiring board after mounting it onto the
matrix substrate 1A, the thermal expansions appearing around the
components affect the connections between the leads thereof and the
terminals corresponding thereto, and the leads will be disconnected
from the terminals depending on the circumstances. The combination
of the flexible wiring board being utilized simply for conductive
paths and the printed circuit board (preferably, more rigid than
the flexible wiring board) for mounting the electronic and/or
electric components in the liquid crystal display device according
to the present invention has an advantage for preventing the
above-mentioned problem.
The signal flows 40 in FIGS. 10A and 10B denotes a starting signal
inputted to the drain driving circuits 6, or a carry signal (also
called an enable signal) being transmitted between the drain
driving circuits 6. The characteristics of this signal will be
explained later with reference to FIG. 7.
The output from the control circuit 12 on the control board 10 is
inputted to the corresponding drain driving circuits 6 via the
connecting part 19A of the drain circuit board 16A and the
connecting part 19B of the drain circuit board 16B, as shown by
dashed lines A and B in FIG. 1.
In the case of this structure, the distances from each of the
connecting portions 19A, 19B of the drain circuit boards 16A, 16B
to the most distant video signal line 4 from the each connecting
portion and to the other video signal line(s) 4 in the vicinity of
the most distant video signal line are shorter than those distances
in a conventional structure, whereby it is possible to prevent
occurrence of the waveform distortion of video signals to be
supplied to the video signal lines 4. The capacity of the
interconnecting lines of the drain circuit boards 16A and 16B are
increased by the drain driving circuits 6 in which circuits which
repeat charging and discharging are incorporated, but such capacity
can be decreased to a great extent by the number of the drain
driving circuits 6 to be mounted on the drain circuit boards 16A
and 16B being reduced to half by using the above-described
structure.
As shown in FIG. 1, a video signal is supplied from a video signal
source 22 to the control board 10 through a cable 23 and an
interface board 24, and is inputted to a control circuit 12 mounted
on the control board 10.
In FIG. 1, the liquid crystal display panel 1, the gate circuit
board 15, the drain circuit boards 16A and 16B and the printed
circuit board 10 are shown to be positioned in approximately the
same plane. Actually, the printed circuit board 10 is bent at a
portion where the gate circuit board 15 and the drain circuit
boards 16A and 16B are mounted, and the bent surface is positioned
at approximately right angles to the liquid crystal display panel 1
(the sheet surface of FIG. 1). This arrangement is based on the
feature of reducing the area of a so-called frame of the liquid
crystal display device. The frame is the area between the outline
of the outer frame of the liquid crystal display device and the
outline of its display portion, and by reducing this area, it is
possible to increase the area of the display portion with respect
to the outer frame.
<Structure of Pixel>
FIG. 3 is a plan view showing in detail the structure of the pixels
2.
Referring to FIG. 3, the scanning signal line 3 and a counter
voltage signal line 50 which are disposed to be extended in the x
direction are formed on the main surface of the transparent
substrate (matrix substrate) 1A. The area surrounded by these
signal lines 3 and 50, and the video signal lines 2 (to be
described later) which are disposed to be extended in the y
direction is a pixel area.
In this embodiment, the counter voltage signal line 50 is formed to
run between the scanning signal lines 3 in parallel therewith, and
pixel areas are respectively formed to extend in the .+-.y
directions from the counter voltage signal line 50.
With this structure, it is possible to reduce the number of the
counter voltage signal lines 50 juxtaposed in the y direction to
approximately half of the conventionally required number, whereby
it is possible to assign the areas occupied by the counter voltage
signal lines 50 to the pixel areas and increase the area of the
pixel areas.
In each of the pixel areas, for example, three counter electrodes
50A which are extended in the y direction are formed at equal
intervals integrally with the counter voltage signal line 50. These
counter electrodes 50A are not connected to but extended to
positions close to the scanning signal line 3, and the outside two
of the counter electrodes 50A are arranged adjacently to the video
signal lines 2 and the remaining one counter electrode 50A is
positioned in the middle (between the outside two counter
electrodes 50A and apart from the same).
Furthermore, an insulation layer made of, for example, a silicon
nitride layer is formed to cover the scanning signal lines 3 and
others, over the main surface of the transparent substrate 1A on
which the scanning signal lines 3, the counter voltage signal lines
50 and the counter electrodes 50A are formed in the above-described
manner. This insulation layer functions as an interlayer insulation
layer for insulating the video signal lines 2 from the scanning
signal lines 3 and the counter voltage signal lines 50, and also
functions as a gate insulation layer for the thin-film transistor
TFT and as a dielectric film for a storage capacitance Cstg.
On the surface of the insulation layer, a semiconductor layer 51 is
formed in an area in which the thin-film transistor TFT is formed.
This semiconductor layer 51 is made of, for example, amorphous Si,
and is formed to be superposed on the scanning signal line 3 in a
portion close to one of the video signal lines 2 which will be
described later. Thus, part of the scanning signal line 3 serves as
the gate electrode of the thin-film transistor TFT.
The video signal lines 2 which are extended in the y direction and
juxtaposed in the x direction are formed on the surface of the
insulation layer. Each of the video signal lines 2 is formed
integrally with a drain electrode 2A which is formed to extend into
a portion of the surface of the semiconductor layer 51 which
constitutes the thin-film transistor TFT.
Furthermore, a pixel electrode 53 which is connected to a source
electrode 53A of the thin-film transistor TFT is formed on the
surface of the insulation layer in the pixel area. This pixel
electrode 53 is formed to be spaced apart from two adjacent ones of
the counter electrodes 50A and to be extended in the y direction
between the two adjacent ones. One end of the pixel electrode 53
also serves as the source electrode 53A of the thin-film transistor
TFT, and the pixel electrode 53 is extended from this one end in
the y direction toward the counter voltage signal line 50 and is
further extended in the x direction along the counter voltage
signal line 50, and is again extended in the y direction, thereby
forming a U-like shape (which is shown as an inverted U-like shape
in FIG. 3).
The portion of the pixel electrode 53 which is superposed on the
counter voltage signal line 50 constitutes the storage capacitance
Cstg which uses the above-described insulation layer as the
dielectric film, in the region between the portion and the counter
voltage signal line 50. By the storage capacitance Cstg, video
information is stored in the pixel electrode 53 for a long time,
for example, when the thin-film transistor TFT is off.
The surface of the semiconductor layer 51 which corresponds to the
interface between the drain electrode 2A and the source electrode
53A of the thin-film transistor TFT is doped with phosphorus (P) to
form a high N-type impurity concentration layer, thereby providing
ohmic contact at each of the drain electrode 2A and the source
electrode 53A. The high impurity concentration layer is formed over
the entire surface of the semiconductor layer 51, and after the
drain electrodes 2A and the source electrodes 53A have been formed,
these electrodes 2A and 53A are used as a mask to etch and
eliminate the portion of the high impurity concentration layer
other than the area in which the electrodes 2A and 53A are formed,
thereby forming the above-described structure.
A protective layer made of, for example, a silicon nitride layer is
formed over the top surface of the insulation layer on which the
thin-film transistors TFT, the video signal lines 2, the pixel
electrodes 53 and the storage capacitances Cstg are formed in the
above-described manner, and an alignment layer is formed over the
top surface of the protective layer, to constitute a so-called
lower substrate of the liquid crystal display panel 1 (which
corresponds to the previously described matrix substrate 1A).
Although not shown, a black matrix (denoted by reference numeral 54
in FIG. 3) which has apertures in portions corresponding to the
respective pixel areas is formed in a liquid-crystal-side portion
of the transparent substrate (color filter substrate) 1B which
constitutes a so-called upper substrate.
Furthermore, color filters are formed to cover the apertures formed
in the portions of the black matrix 54 which correspond to the
respective pixel areas. These color filters have colors which
differ from those between adjacent pixel areas in the x direction,
and the respective color filters have boundaries on the black
matrix 54.
A flat layer made from a resin layer or the like is formed over the
surface on:
which the black matrix 54 and the color filters are formed in this
manner, and an alignment layer is formed over the surface of the
flat layer.
<Peripheral Structure of Gate Driving Circuit>
FIGS. 4A and 4B are views showing the details of the structure of
the gate driving circuits 5 and the peripheral structure thereof.
FIG. 4A is a plan view showing the portion of a frame P surrounded
by dot-dashed lines in FIG. 1, and FIG. 4B is a cross-sectional
view taken along line b-b of FIG. 4A.
In FIGS. 4A and 4B, the scanning signal lines 3 are formed to be
extended from the right side as viewed in the figures over the
surface of the transparent substrate (matrix substrate) 1A. These
scanning signal lines 3 are divided into groups each including
adjacent scanning signal lines, and the scanning lines which belong
to each of the groups are bent to converge toward the gate driving
circuit 5 and terminals are formed at the converging ends of the
respective scanning lines.
These respective terminals are disposed to correspond to electrodes
(bumps) on the output side of the gate driving circuit 5, and the
terminals is equal in pitch to the electrodes.
Each of the gate driving circuits 5 is constructed of a
semiconductor integrated circuit (IC), and is mounted on the
transparent substrate 1A (facedown-bonding) with its surface on
which the electrodes are formed being faced down.
Interconnecting layers which are respectively connected to
electrodes (bumps) on the input side of each of the gate driving
circuits 5 are formed over the transparent substrate 1A, and are
extended to a peripheral edge of the transparent substrate 1A.
The extended portions of the interconnecting layers constitute
portions to be connected to terminals formed on the gate circuit
board 15, and the extended portions is equal in pitch to the
terminals.
As described previously, signals from the control circuit 12 on the
control board 10 are inputted to the respective gate driving
circuits 5 via interconnecting lines formed on the gate circuit
board 15, and the output from each of the gate driving circuits 5
is supplied to the scanning signal lines 3.
FIG. 5 shows the relationship between individual signals to be
inputted to each of the gate driving circuits 5 via the gate
circuit board 15 (i.e., individual signals outputted from the
control circuit 12) and signals to be supplied from each of the
gate driving circuits 5 to the corresponding scanning signal lines
3.
The line 30 transmits a starting signal for the gate driving
circuit G1 as disposed at a first stage in a scanning, or a carry
signal (also called an enable signal) for the gate driving circuit
G1 as disposed at a stage other than the first stage therein. The
starting signal or the carry signal being supplied from the line 30
to the terminal Yg1 of the gate driving circuit G1 has a wave form
30 shown at a right side in FIG. 5. When the wave form 30 shows
"High", the scanning sequence in the gate driving circuit G1 is
triggered.
The line 31 transmits a shift clock signal for regulating a
scanning sequence. The shift clock signal is supplied from the line
31 to the terminal Yg2 of each of the gate driving circuits G1, G2,
etc. in parallel, and has a wave form 31 shown at a right side in
FIG. 5.
The lines 32 supply electric powers for the gate driving circuits.
The lines 33 and 34 supply voltages utilized for outputs of the
gate driving circuits, one of the lines supplies a voltage
corresponding to a high level of the outputs, and another of the
lines supplies a voltage corresponding to a low level thereof. The
line 35 transmits a signal for reversing the scanning sequence from
downward direction to upward direction and vice versa in FIG. 5.
Each of the gate driving circuits G1, G2, etc. has twelve terminals
for outputting signals for regulating the switching elements TFT
through each of the scanning signal lines 3 shown in FIG. 1. As the
wave forms 36 outputted from the terminals Xg1, Xg2, Xg3, and Xg12
show "Highs" one by one, each of the signals outputted from the
twelve terminals Xg1 through Xg12 shows "High" successively in
accordance with that of the shift clock signal 31.
When the scanning sequence in the gate driving circuit G1 is
finished, the carry signal (called the enable signal, also) is
outputted from the terminal Yg8 of the gate driving circuit G6 and
inputted to the terminal Yg1 of the gate driving circuit G2. The
carry signal outputted from the terminal Yg8 of the gate driving
circuit G1 has a wave form 37 shown at a right side in FIG. 5, and
the "High" output thereof triggers off the scanning sequence in the
gate driving circuit G2 as the signal wave form outputted from the
terminal Xg1 of the gate driving circuit G2.
<Peripheral Structure of Drain Driving Circuit>
FIGS. 6A and 6B are views showing the details of the structure of
the drain driving circuits 6 and the peripheral structure thereof.
FIG. 6A is a plan view showing the portion of a frame Q :surrounded
by dot-dashed lines in FIG. 1, and FIG. 6B is a cross-sectional
view taken along line b-b of FIG. 6A.
As is apparent from FIGS. 6A and 6B, the structure of the drain
driving circuits 6 (called the video signal driving circuits, or
the source driving circuits, also) and the peripheral structure
thereof are nearly similar to the structure of the gate driving
circuits 5 and the peripheral structure thereof.
The peripheral structure of the drain driving circuits, 6 differs
from that of the gate driving circuits 5 in that, as described
previously with reference to FIG. 1, among the drain driving
circuits 6 juxtaposed in the x direction of FIG. 1, each of the
drain driving circuits 6 included in the left-half group is
supplied with a signal from the drain circuit board 16A, while each
of the drain driving circuits 6 included in the right-half group is
supplied with a signal from the drain circuit board 16B.
FIG. 7 shows the relationship between individual signals to be
inputted to each of the drain driving circuits 6 via the drain
circuit board 16A (i.e., individual signals outputted from the
control circuit 12) and signals to be supplied from each of the
drain driving circuits 6 to the corresponding video signal lines
4.
The line 40 transmits a starting signal for the drain driving
circuit D1 as disposed at a first stage in a video signal
acquisition, or a carry signal (also called an enable signal) for
the drain driving circuit D1 as disposed at a stage other than the
first stage therein. The starting signal or the carry signal being
supplied from the line 40 to the terminal Yg1 of the drain driving
circuit D1 has a wave form 40 shown at a right side in FIG. 7. When
the wave form 40 shows "High", the scanning sequence in the drain
driving circuit D1 is triggered.
The line 41 transmits a clock signal for regulating a video signal
acquisition sequence. The clock signal is supplied from the line 41
to the terminal Yg2 of each of the drain driving circuits D1, D2,
etc. in parallel, and has a wave form 41 shown at a right side in
FIG. 7.
The line 42 transmits a clock signal for regulating output timings
for liquid crystal driving voltage supplied from the drain driving
circuits to the video signal lines 4. The clock signal is supplied
from the line 42 to the terminal Yg3 of each of the drain driving
circuits D1, D2, etc. in parallel, and has a wave form 42 shown at
a right side in FIG. 7. The wave form 42 has an inverted shape of
that of the aforementioned shift clock signal 31.
The two lines 43 supply electric powers for the drain driving
circuits. The four lines 44 supply voltages utilized for outputs of
the drain driving circuits, and the respect voltages being supplied
thereby have different values from each other in accordance with
gray scales to be displayed in the liquid crystal display
panel.
The three lines 45 transmit the video signals for determining a
voltage outputted from each of the terminal Xg1 through Xg15 of the
respective drain driving circuits D1, D2, etc. Each of the video
signals has either a "High" state (so-called "1") or a "Low" state
(so-called "0") as'shown by a "Eye-diagram" at the right side in
FIG. 7. The drain driving circuit D1 acquires the respective video
signals corresponding to the terminals thereof Xg1 through Xg15,
and accumulates the data therein sequentially. When the video
signal acquisition in the drain driving circuit D1 is finished, the
carry signal (called the enable signal, also) is outputted from the
terminal Yg14 of the drain driving circuit D1 and inputted to the
terminal Yg1 of the drain driving circuit D2. The carry signal
outputted from the terminal Yg14 of the drain driving circuit D1
has a wave form 48 shown at a right side in FIG. 7, and the "High"
output thereof triggers off the video signal acquisition in the
drain driving circuit D2 in a similar manner to that in the drain
driving circuit D1 mentioned above. The video signal acquisitions
and data accumulations thereof for each of the plurality of the
drain driving circuits being juxtaposed along one side of the
liquid crystal display panel 1 (as shown in FIG. 1) are progressed
successively by the carry signal transmission therebetween. When
the video signal acquisitions and data accumulations are finished,
each of the plurality of the drain driving circuits outputs the
voltage signals from the terminals thereof Xg1 through Xg15 to the
respective video signal lines 4 corresponding thereto. Each of the
plurality of the drain driving circuits determines the voltages to
be outputted from the respective terminals Xg1 through Xg15 (the
gray scales for the respective video signal lines 4, in other
words) in accordance with the data being accumulated during the
aforementioned video signal acquisition process, selects a proper
voltage from the four kinds of voltages supplied by the lines 44,
and supplies the respective proper voltages from the terminals Xg1
through Xg15 to the video signal lines 4. Therefore, the voltage
being outputted from each of the terminals Xg1 through Xg15 may
take several kinds of values as the wave forms 47 shows, and has a
different wave form from those of the aforementioned twelve
terminals Xg1 through Xg12 of the gate driving circuits G1, G2,
etc.
The line 46 transmits a signal for reversing the sequence for
acquiring the video signals from downward direction to upward
direction and v.v. in FIG. 7.
FIGS. 6A and 6B show the state in which the drain driving circuits
6 are juxtaposed in the x direction, whereas FIG. 7 shows the state
in which the drain driving circuits 6 are juxtaposed in the y
direction.
<Flexible Wiring Board>
FIG. 8 shows a cross section of each of the gate circuit board 15,
the drain circuit board 16A and the drain circuit board 16B. As is
apparent from FIG. 8, each of the circuit boards 15, 16A and 16b is
formed of a multilayered structure. An interconnecting layer 61
made of Cu (copper) is formed over a surface of a substrate made
from a polyimide film 60, and the surface (the top surface as
viewed in FIG. 8) of the interconnecting layer 61 is coated with Cu
plating 62. Layers each having such stacked structure are bonded
together by an adhesive 63, to constitute the multilayered
structure.
The interconnecting layers of the respective layers are
electrically connected to one another by a conductive material
charged in a through-hole 64 formed through the overlapping
portions of the interconnecting layers. The "Multi-Layered Section"
in FIG. 8 contains at least two conductor layers (three Cu-layers
61, in FIG. 8) being stacked on each other and spaced by insulating
layer (a polyimide film 60, in FIG. 8).
In this case, a portion connected to the liquid crystal display
panel 1 is made from a single Cu interconnecting layer 61, and its
terminal is coated with Au plating 65. The "Mono-Layered Section"
in FIG. 8 has a single conductor layer like the single Cu
interconnecting layer 61.
Other Embodiments
The above-described embodiment is constructed in such a manner that
the output from the control circuit 12 is inputted to each of the
two drain circuit boards 16A and 16B connected to the drain driving
circuit 6.
This structure is intended to restrain the occurrence of waveform
distortion of video signals to be supplied to the video signal
lines.
However, if it is only necessary to achieve the purpose of
preventing harmful effects due to the thermal expansion of the
drain circuit boards 16A and 16B, instead of the above-described
structure, it is also preferable to adopt a structure in which the
output from the control circuit 12 is inputted to the drain circuit
board 16A and further to the drain circuit board 16B via the drain
circuit board 16A.
For example, the drain circuit boards 16A and 16B merely take the
form of being divided from each other, and the signal transmission
path of each of the drain circuit boards 16A and 16B has a
structure similar to that of a conventional signal transmission
path.
One specific example of such signal transmission path will be
described below with reference to FIG. 1. As shown, the drain
circuit board 16A is mechanically and electrically connected to the
control board 10 at the connecting part 19A, whereas the drain
circuit board 16B is only mechanically connected to the control
board 10 at the connecting part 19B and does not allow transmission
nor reception of signals and electric power at the connecting part
19B. In addition, joiners for providing electrical connection
between the drain circuit boards 16A and 16B are disposed between
the same, and interconnecting layers for transmitting signals to
the interconnecting layers of the drain circuit board 16B are
formed over the drain circuit board 16A. Accordingly, signals
outputted to the drain circuit board 16B from the control board 10
pass through the connecting part 19A, the drain circuit board 16A
and the joiners, and are inputted to the drain driving circuits 6
which correspond to the drain circuit board 16B.
In the above-described embodiment, the two drain circuit boards 16A
and 16B are connected to the drain driving circuits 6, and the
connecting portions 19A and 19B of the respective drain circuit
boards 16A and 16B which are connected to the control board 10 are
formed on the respective two drain circuit boards 16A and 16B in
such a manner that the connecting portions 19A and 19B are
respectively located on the same sides of the drain circuit boards
16A and 16B (on the left sides of the drain circuit boards 16A and
16B as viewed in FIG. 1).
However, needless to say, the drain circuit boards 16A and 16B may
be constructed in such a manner that, as shown in FIG. 9, the
respective connecting portions 19A and 19B are arranged adjacently
to each other (along the longitudinal direction of the drain
circuit boards 16A and 16B).
In this case, the control circuit 12 is arranged between the
connecting portions 19A and 19B and the output from the control
circuit 12 is supplied to the drain circuit boards 16A and 16B via
the respective connecting portions 19A and 19B, whereby the
distance between the control circuit 12 and the video signal line 4
located at the most distant position from the control circuit 12 is
reduced to a great extent.
This structure makes it possible to reduce the occurrence of the
waveform distortion of a video signal to be supplied to the video
signal line 4 which is located at the most distant position from
the control circuit 12 as well as the waveform distortion of a
video signal to be supplied to the video signal line or lines 4
near the most distant video signal line 4.
Further variations of the flexible wiring boards being utilized for
the liquid crystal display device according to the present
invention are shown in FIGS. 11A, 11B, and 11C.
For both the gate driving circuits 5 and the drain driving circuits
6, the carry signal (the enable signal) 30, 40 should be
transmitted between the driving circuits sequentially. Each of the
variations in FIGS. 11A, 11B, and 11C has a suitable structure for
reducing lengths of signal paths, esp. between the flexible wiring
boards 16A, 16B, 16C, or so on. Each of these variation also
reflects an area of the flexible wiring board which should be
formed as the aforementioned Multi-Layered Section MUL.
As mentioned previously, the flexible wiring boards 16A, 16B, 16C
juxtaposed along the matrix substrate 1A shown in FIG. 11A are
separated from each other to reduce the thermal expansions.
However, as the carry signal 40 being outputted from one drain
driving circuit 6 facing the right-end of the flexible wiring board
16A has to be transmitted backward to the connecting portion 19A,
to pass through the printed circuit board 10, and to be inputted to
another drain driving circuit 6 (adjacent to the one drain driving
circuit 6) facing the left-end of the flexible wiring board 16B.
Such a long signal path may deform the signal wave form of the
carry signal 40 on the way to the drain driving circuits 6
corresponding to the flexible wiring board at a next stage. For
preventing this possible problem, joint members 160 are provided
between the flexible wiring boards 16A and 16B and between the
flexible wiring boards 16B and 16C. Both of the joint members 160
have a signal path for transmitting the carry signal 40
therethrough. The signals other than the carry signal 40 may be
transmitted through the joint members. However, the thickness of
the joint members 160 should take priority to absorb both thermal
expansions of the flexible wiring, boards being connected thereby.
While thermal expansion appears regardless of the thickness of the
flexible circuit board, the thermal expansion is reduced by
dividing the flexible circuit board by the member being thinner
than the flexible circuit board. Thus, the joint member should be
thinner than the portion of the flexible circuit board to which the
joint member 160 is connected. For this purpose, reducing a number
of conductor layers in the joint member 160 in contrast to that in
the portion is recommended, and more preferably, the joint member
160 should be formed of the aforementioned mono-layered
structure.
The variation shown in FIG. 11B is a modification of the flexible
wiring board of FIG. 2 on the same basis as that of FIG. 11A. The
flexible wiring boards 16A, 16B, and 16C are combined by portions
narrowed by the slits (called narrowed portions, hereinafter), and
the carry signal 40 is transmitted between the flexible wiring
boards adjacent to one another through the portion. Both of the
slits defining the narrowed portions get into the width direction
of the flexible wiring board longer than the other slits dividing
the aforementioned protruding portions. It is apparent from the
multilayered section, that each of the flexible wiring boards are
separated by the mono-layered section MON of the narrowed portion.
According to this structural feature, the thermal expansions
appearing at the respective flexible wiring boards are absorbed by
the narrowed portion. Although the slit defining the narrowed
portion is shorter than the other slits dividing the protruding
portions in the width direction of the flexible wiring board or the
narrowed portion has the aforementioned multi-layered structure
thinner than that of the flexible wiring board, a similar advantage
to that of the structure of FIG. 11B can be obtained. The combined
flexible wiring board of FIG. 11B has one of the best structures
for reducing influence of the thermal expansions of the respective
flexible wiring boards upon the combined structure thereof.
The structure of FIG. 11C is different from those of FIGS. 11A and
11B. The flexible wiring boards 16A, 16B, and 16C in FIG. 11C are
not connected to one another, but each of the flexible wiring
boards has a pair of the connecting portion. As FIG. 11C shows, one
of the flexible wiring boards 16A has a first connecting portion
19A at the left side thereof and a second connecting portion 19N at
the right side thereof. According to this structure, the carry
signal 40 being outputted from one drain driving circuit 6 facing
the right-end of the flexible wiring board 16A is transmitted
through the second connecting portion 19A' of the flexible wiring
board 16A, the printed circuit board 10, and the first connecting
portion 19B of the flexible wiring board 16B, to be inputted to
another drain driving circuit 6 (adjacent to the one drain driving
circuit 6) facing the left-end of the flexible wiring board 16B.
Although the path length of the carry signal 40 between the
flexible wiring boards adjacent to one another in FIG. 11C becomes
longer than those in FIGS. 11A and 11B, the similar advantage to
those for the structures of FIG. 11A and 11B is obtained. The
structure of FIG. 11C has further advantage to prevent electric
power or signal intensity other than the carry signal from becoming
weaker in accordance with a distance from the connecting portion.
In FIG. 11C, the electric power supplying line for the drain
driving circuits 43 is extending from the source circuit 11 into
the flexible wiring board 16A through not only the connecting
portion 19A but also the connecting portion 19A'. According to this
structure, the voltage drop of the electric power for the drain
driving circuits 43 inside the flexible wiring board is
prevented.
In the above description of each of the embodiments, reference has
been made to an improvement in the drain circuit boards 16A and 16B
for the drain driving circuits 6. However, needless to say, the
present invention can also be applied to the gate circuit board 15
for the gate driving circuits 5.
This is because the gate circuit board 15 for the gate driving
circuits 5 and the drain circuit boards 16A and 16B for the drain
driving circuits 6 differ from each other only in the kind of
signal to be supplied and are completely the same in mechanical
structure, and also because a similar problem occurs if the size of
the liquid crystal display panel 1 becomes far larger and the side
of the liquid crystal display panel 1 that is adjacent to the gate
driving circuits 5 becomes far longer.
In the above description of each of the embodiments, reference has
been made to a liquid crystal display device of the so-called
lateral electric field type. However, needless to say, the present
invention can also be applied to a so-called vertical electric
field type.
The vertical electric field type of liquid crystal display device
which has been used herein represents a liquid crystal display
device having a structure in which transparent electrodes are
respectively formed over the liquid-crystal-side surfaces of
transparent substrates which are disposed to oppose each other
across a liquid crystal and an electric field is produced in the
liquid crystal by the potential difference between the
electrodes.
As long as, in such a liquid crystal display device, driving
circuits mounted on its liquid crystal display panel, flexible
wiring boards, printed circuit boards and the like have structures
similar to those of the previously described corresponding ones,
the present invention can be applied to the liquid crystal display
device without any modification.
As is apparent from the foregoing description, in accordance with
the liquid crystal display device according to the present
invention, in spite of an increase in the size of a liquid crystal
display panel, it is possible to prevent the defective connection
of a flexible wiring board to a transparent substrate of the liquid
crystal display panel.
In addition, in spite of an increase in the size of the liquid
crystal display panel, it is possible to prevent waveform
distortion from occurring in a signal on a signal line which lies
on one side of the liquid crystal display panel in the direction of
juxtaposition of signal lines.
While we have shown and described several embodiments in accordance
with the present invention, it is understood that the same is not
limited thereto but is susceptible of numerous changes and
modifications as known to those skilled in the art, and we
therefore do not wish to be limited to the details shown and
described herein but intend to cover all such changes and
modifications as are encompassed by the scope of the appended
claims.
* * * * *