U.S. patent application number 12/259615 was filed with the patent office on 2009-03-05 for liquid crystal display device.
Invention is credited to Shinya Hashimoto, Hiroyuki TAKAHASHI, Takahiro Yamada.
Application Number | 20090058783 12/259615 |
Document ID | / |
Family ID | 29243805 |
Filed Date | 2009-03-05 |
United States Patent
Application |
20090058783 |
Kind Code |
A1 |
TAKAHASHI; Hiroyuki ; et
al. |
March 5, 2009 |
LIQUID CRYSTAL DISPLAY DEVICE
Abstract
LCD device including: a first LCD panel for displaying an image
in a transmission mode; a second LCD panel for displaying an image
in a reflection mode; and a power supply circuit for supplying a
first counter voltage for displaying in the transmission mode to a
first counter electrode of the first LCD panel and a second counter
voltage for displaying in the reflection mode to a second counter
electrode of the second LCD panel, wherein the first counter
voltage and the second counter voltage are at voltage levels
mutually different from one another.
Inventors: |
TAKAHASHI; Hiroyuki;
(Funabashi, JP) ; Hashimoto; Shinya; (Mobara,
JP) ; Yamada; Takahiro; (Mobara, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
29243805 |
Appl. No.: |
12/259615 |
Filed: |
October 28, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10411267 |
Apr 11, 2003 |
7453434 |
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12259615 |
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Current U.S.
Class: |
345/94 |
Current CPC
Class: |
G02F 1/13456 20210101;
G09G 3/3655 20130101; G09G 3/3406 20130101; G09G 2300/0456
20130101; G09G 2320/0247 20130101; G09G 2300/0408 20130101 |
Class at
Publication: |
345/94 |
International
Class: |
G09G 3/36 20060101
G09G003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 2002 |
JP |
2002-126432 |
Claims
1. A liquid crystal display device comprising: a first liquid
crystal display panel for displaying an image in a transmission
mode, the first liquid crystal display panel having a number of
first pixel electrodes, a first counter electrode for applying an
electric field between itself and the first pixel electrodes, and a
first liquid crystal layer interposed between the first pixel
electrodes and the first counter electrode; a second liquid crystal
display panel for displaying an image in a reflection mode, the
second liquid crystal display panel having a number of second pixel
electrodes, a second counter electrode for applying an electric
field between itself and the second pixel electrodes, and a second
liquid crystal layer interposed between the second pixel electrodes
and the second counter electrode; and a power supply circuit for
supplying a first counter voltage for displaying in the
transmission mode to the first counter electrode of the first
liquid crystal display panel and a second counter voltage for
displaying in the reflection mode to the second counter electrode
of the second liquid crystal display panel, wherein the first
counter voltage and the second counter voltage are at voltage
levels mutually different from one another.
2. A liquid crystal display device according to claim 1, wherein
the first counter voltage is a voltage optimized for displaying in
the transmission mode, and the second counter voltage is a voltage
optimized for displaying in the reflection mode.
3. A liquid crystal display device according to claim 1, wherein
the power supply circuit has a first counter voltage generation
circuit for applying the first counter voltage to the first counter
electrode of the first liquid crystal display panel, and a second
counter voltage generation circuit for applying the second counter
voltage to the second counter electrode of the second liquid
crystal display panel.
4. A liquid crystal display device according to claim 1, wherein
the first counter voltage is lower than the second counter
voltage.
5. A liquid crystal display device according to claim 1, wherein
the first liquid crystal display panel has a first substrate and a
second substrate sandwiching the first liquid crystal layer
therebetween, the second liquid crystal display panel has a third
substrate and a fourth substrate sandwiching the second liquid
crystal layer therebetween, the first substrate is separated from
the third substrate and the fourth substrate, and the second
substrate is separated from the third substrate and the fourth
substrate.
6. A liquid crystal display device according to claim 1,
comprising: an illumination device disposed at a back face of the
first liquid crystal display panel, wherein the power supply
circuit applies the first counter voltage to the first counter
electrode of the first liquid crystal display panel when the
illumination device is on, and the power supply circuit applies the
second counter voltage to the second counter electrode of the
second liquid crystal display panel when the illumination device is
off.
7. A liquid crystal display device according to claim 1, wherein
the first liquid crystal display panel has a first substrate and a
second substrate sandwiching the first liquid crystal layer
therebetween, the second liquid crystal display panel has a third
substrate and a fourth substrate sandwiching the second liquid
crystal layer therebetween, the first liquid crystal display panel
has a first active matrix array, and the second liquid crystal
display panel has a second active matrix array.
8. A liquid crystal display device according to claim 1, wherein
the first liquid crystal display panel has a first image signal
line supplying image signals to the first pixel electrodes, the
second liquid crystal display panel has a second image signal line
supplying image signals to the second pixel electrodes, the first
image signal line is electrically connected to the second image
signal line, and the first image signal line and the second image
signal line are driven by an image signal drive circuit in common.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a continuation of U.S. application Ser. No.
10/411,267, filed Apr. 11, 2003. This application relates to and
claims priority from Japanese Patent Application No. 2002-126432,
filed on Apr. 26, 2002. The entirety of the contents and subject
matter of all of the above is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates in general to liquid crystal
display devices; and, more particularly, the invention relates to a
liquid crystal display device of the type having a transmissive
display region or area and a reflective display area in every
picture element, and also having two-mode display functions,
including a transmission mode and a reflection mode.
[0003] Liquid crystal display devices offer several features, such
as slim size and light weight, plus low power consumption, and thus
they are widely employed as image/text data display devices in a
variety of types of information equipment typically including
personal computers (PCs), and they are also used in portable or
mobile information terminals, digital cameras and camera-embedded
video tape recorders (VTRs). In recent years, the demand for low
power consumption is becoming stronger in accordance with rapid
popularization of small-size digital equipment, such as, in
particular, handheld wireless telephone handsets, known as cellular
phones, and mobile information terminals and the like.
[0004] Most liquid crystal display devices for use in personal
computers and liquid crystal display monitors are generally of the
type employing a transmission-type display mode (simply referred to
as a transmission mode hereinafter) which visualizes images by
controlling the transmission amount of light emitted from an
illumination device--this is typically installed on the back face
of a liquid crystal display panel and is called a back-light--on
the liquid crystal display panel side. However, the electrical
power being consumed by the backlight amounts for more than 50
percent (%) of the power that is consumed by the entire liquid
crystal display device. Due to this, in battery-driven small-size
equipment, such as cellular handy phones and mobile information
terminals and the like, the length of the operating time thereof is
significantly limited.
[0005] In view of this, these small-size electronic devices are
often designed to employ liquid crystal display devices of the type
using a reflection-type display mode (simply referred to hereafter
as a reflection mode) which visualizes images by permitting
reflection of ambient light without the use of any backlight. Such
reflection of ambient light is achievable by providing a reflective
plate on the outer surface or inner surface of a liquid crystal
display panel, or alternatively by adding reflecting functions to
the pixel-forming electrodes.
[0006] The reflection mode liquid crystal display devices are faced
with a problem that the visual recognizability or viewability of an
on-screen display decreases when the ambient light is less in
intensity (i.e. in the dark). For equipment such as cellular phones
that are being used everywhere without regard to indoor and outdoor
environments, it is necessary to offer required usability
irrespective of whether the ambient light is bright or dark. As a
remedy for this, a liquid crystal display device of the
partial-transmission/partial-reflection type has been proposed,
which device has both transmission-mode display functionality, and
reflection-mode display functionality with a transmission mode
display area and a reflection mode display area being formed in the
region of a single picture element or "pixel" (see
JP-A-2000-19563).
[0007] Unfortunately, in the transmission mode display and the
reflection mode display, there are different optimal values for the
voltages which are applied between a pixel electrode and an
opposite or "counter" electrode in order to create an appropriate
electric field in a liquid crystal layer. The optimal voltage as
stated herein refers to a voltage which is provided at the time of
obtaining flicker-free on-screen images. In most cases, an optimal
voltage in the transmission mode is lower in potential than that in
the reflection mode.
[0008] In the prior known partial-transmissive/reflective liquid
crystal display device referred to above, the voltage being applied
to the counter electrode in order to form an electric field between
it and the counter electrode is simply set to the same level in any
display mode, i.e. of either the transmission mode or the
reflection mode. Accordingly, even when onscreen images are of good
quality in the transmission mode, flicker can occur on the display
screen when the display mode is switched to the reflection mode,
resulting in a decrease in display image quality.
[0009] It is therefore an object of the present invention to
provide a liquid crystal display device of the
partial-transmission/reflection type having displaying functions in
both a transmission mode and a reflection mode, which device is
capable of improving the image quality in each display mode to
thereby obtain high-quality on-screen display images in either
display mode.
SUMMARY OF THE INVENTION
[0010] To attain the foregoing object, this invention provides a
liquid crystal display device having a principal arrangement which
provides counter voltages that are optimized for respective ones of
the transmission mode and the reflection mode and applies a
selected one of them to a counter electrode in accordance with
selection of these display modes. Representative arrangements of
this invention will be described below.
[0011] (1) A liquid crystal display device includes a liquid
crystal display panel having a number of pixel electrodes with two
display mode functions, including a transmission mode and a
reflection mode, a counter electrode for applying an electric field
between itself and the pixel electrodes, and a liquid crystal layer
interposed between the pixel electrodes and the counter electrode,
and a counter voltage generation circuit for applying to the
counter electrode an optimal voltage with respect to a respective
display mode of the transmission mode and the reflection mode.
[0012] (2) In (1), the liquid crystal display device further
includes an illumination device disposed at the back face of the
liquid crystal display device, wherein the counter voltage
generation circuit applies to the counter electrode a voltage
different during turn-on of the illumination device than it is
during turn-off thereof.
[0013] (3) A liquid crystal display device includes a liquid
crystal display panel having a number of pixel electrodes with two
display mode functions, including a transmission mode and a
reflection mode, a counter electrode for applying an electric field
between itself and the pixel electrodes, and a liquid crystal layer
to which the electric field is applied, and a counter voltage
generation circuit for applying to the counter electrode a
different voltage with respect to a respective display mode of the
transmission mode and the reflection mode.
[0014] (4) In (3), the liquid crystal display device further
includes an illumination device disposed at a back face of the
liquid crystal display panel, wherein the counter voltage
generation circuit applies to the counter electrode a voltage for
use in the transmission mode when the illumination device turns on
and applies a voltage for use in the reflection mode when the
illumination device turns off.
[0015] (5) A liquid crystal display device includes a liquid
crystal display panel having a liquid crystal layer interposed
between a main surface of a first substrate and a main surface of a
second substrate, a number of scan signal lines extending in a
first direction of the main surface of the first substrate and
being provided in parallel with a second direction, a number of
image signal lines extending in the second direction and being
provided in parallel to the first direction while being disposed to
cross the scan signal lines, an active element disposed at each
crossing portion of the scan signal lines and the image signal
lines for control of turn-on and turn-off of a pixel, a pixel
electrode driven by the active element and having two display mode
functions of a transmission mode and a reflection mode, and a
counter electrode formed above the main surface of the first
substrate or the second substrate for generating an electric field
between itself and the pixel electrode, a scan signal line drive
circuit for applying a scan signal to the scan signal lines, an
image signal line drive circuit for applying an image signal to the
image signal lines, and a power supply circuit for supplying
necessary voltages to the scan signal line drive circuit and the
image signal line drive circuit along with the counter electrode,
wherein the power supply circuit has a counter voltage generation
circuit for applying a first counter voltage to the counter
electrode in the transmission mode and for applying thereto a
second counter voltage different from the first counter voltage in
the reflection mode.
[0016] (6) In (5), the liquid crystal display device further
includes an illumination device disposed at a back face of the
liquid crystal display panel, wherein the counter voltage
generation circuit applies to the counter electrode the first
counter voltage when the illumination device turns on and applies
thereto the second counter voltage when the illumination device
turns off.
[0017] (7) In (5), the liquid crystal display device further
includes an illumination device disposed on the back face of the
liquid crystal display panel, and a counter voltage selector
circuit provided in the image signal line drive circuit for
applying a counter voltage select signal to the counter voltage
generation circuit while distinguishing between the turn-on and
turn-off of the illumination device, wherein the counter voltage
generation circuit is operatively responsive to receipt of the
counter voltage select signal for applying the first counter
voltage to the counter electrode when the illumination device turns
on and for applying thereto the second counter voltage when the
illumination device turns off.
[0018] (8) In (7), the liquid crystal display device further
includes a group of terminals provided at a peripheral part of the
liquid crystal display panel for inputting a display-use signal and
a voltage from an external signal source to the scan signal line
drive circuit and the image signal line drive circuit, and a
flexible printed circuit board having one end connected to the
terminal group and the other end connected to the external signal
source, wherein the power supply circuit Is mounted on the flexible
printed circuit board.
[0019] (9) A liquid crystal display device includes: a first liquid
crystal display panel which is used for displaying an image in a
transmission mode, which panel has a number of first pixel
electrodes, a first counter electrode for applying an electric
field between itself and the first pixel electrodes, and a first
liquid crystal layer interposed between the first pixel electrodes
and the first counter electrode; a second liquid crystal display
panel which is used for displaying an image in a reflection mode,
which panel has a number of second pixel electrodes, a second
counter electrode for applying an electric field between itself and
the second pixel electrodes, and a second liquid crystal layer
interposed between the second pixel electrodes and the second
counter electrode; a first counter voltage generation circuit for
applying a first counter voltage optimized for display of the
transmission mode to the first counter electrode of the first
liquid crystal display panel; and a second counter voltage
generation circuit for applying a second counter voltage optimized
for display of the reflection mode to the second counter electrode
of the second liquid crystal display panel.
[0020] (10) A liquid crystal display device includes:
a first liquid crystal display panel having a first liquid crystal
layer interposed between a main surface of a first substrate and a
main surface of a second substrate, a number of first scan signal
lines extending in a first direction of the main surface of the
first substrate and being provided in parallel with a second
direction thereof, a number of first image signal lines extending
in the second direction and being provided in parallel to the first
direction while being disposed to intersect the first scan signal
lines, a first active element disposed at each crossing portion of
the first scan signal lines and the first image signal lines for
controlling turn-on and turn-off of a pixel, a first pixel
electrode driven by the first active element for performing
displaying in a transmission mode, and a first counter electrode
formed at the main surface of either the first substrate or the
second substrate for generating an electric field between itself
and the first pixel electrode;
[0021] a second liquid crystal display panel having a second liquid
crystal layer interposed between a main surface of a third
substrate and a main surface of a fourth substrate, a number of
second scan signal lines extending in the first direction of the
main surface of the third substrate and being provided in parallel
with the second direction thereof, a number of second image signal
lines extending in the second direction and being provided in
parallel to the first direction while being disposed to intersect
the second scan signal lines, a second active element disposed at
each crossing portion of the second scan signal lines and the
second image signal lines for controlling turn-on and turn-off of a
pixel, a second pixel electrode driven by the second active element
for performing displaying in a reflection mode, and a second
counter electrode formed at the main surface of either the third
substrate or the fourth substrate for generating an electric field
between itself and the second pixel electrode;
[0022] a scan signal line drive circuit for applying scan signals
to the first scan signal lines provided at the first liquid crystal
display panel and the second scan signal lines provided at the
second liquid crystal display panel;
[0023] an image signal drive circuit for applying first image
signals to the first image signal lines provided at the first
liquid crystal display panel and for applying second image signals
to the second image signal lines provided at the second liquid
crystal display panel; and
[0024] a power supply circuit for supplying necessary voltages to
the scan signal line drive circuit and the image signal line drive
circuit and for supplying a first counter voltage optimized for the
transmission mode to the first counter electrode of the first
liquid crystal display panel and also a second counter voltage
optimized for the reflection mode to the second counter electrode
of the second liquid crystal display panel.
[0025] (11) In (10), the power supply circuit includes a counter
voltage generation circuit for generation of the first counter
voltage and the second counter voltage which are made optimal to
respective display modes of the transmission mode and the
reflection mode.
[0026] (12) In (11), the liquid crystal display device further
includes an illumination device disposed on a back face of the
first liquid crystal display panel, and a counter voltage selector
circuit provided in the image signal line drive circuit for
distinguishing between turn-on and turn-off of the illumination
device and for applying a counter voltage select signal to the
counter voltage generation circuit, wherein the counter voltage
generation circuit is responsive to receipt of the counter voltage
select signal for applying the first counter voltage to the first
counter electrode when the illumination device turns on and for
applying the second counter voltage to the second counter electrode
when the illumination device turns off.
[0027] (13) In (12), the liquid crystal display device further
includes a group of terminals provided at a peripheral part of the
first liquid crystal display panel for inputting a display-use
signal and a voltage from an external signal source to the scan
signal line drive circuit and the image signal line drive circuit,
and a flexible printed circuit board having one end connected to
the terminal group and the other end connected to the external
signal source, wherein the power supply circuit is mounted on the
flexible printed circuit board.
[0028] An effect in each of the above-noted arrangements will be
explained. As recited in paragraph (1) above, a principal concept
of the present invention lies in the fact that the liquid crystal
display device is equipped with a counter voltage generation
circuit which applies to the counter electrode opposing a pixel
electrode an optimal voltage for a respective display mode of
either the transmission mode and the reflection mode. As previously
stated, the voltage used to create an electric field between the
pixel electrode and the counter electrode is different in value
between the transmission mode and the reflection mode.
[0029] In particular, in a partial-transmissive/reflective liquid
crystal display device of the type having both a transmission mode
displaying function and a reflection mode display function with a
transmission mode display area and a reflection mode display area
formed in a single pixel area, the pixel electrode as provided on
or above its liquid crystal display panel is constituted from an
optically transmissive portion made for example of indium-tin-oxide
(ITO) and a reflective portion made of aluminum (Al) or molybdenum
(Mo) or chromium (Cr) or any alloys thereof. Due to this,
electrodes are different from each other in work function with
respect to the liquid crystal layer. In addition, the transmissive
portion and the reflective portion are different from each other in
distance relative to the counter electrode.
[0030] Accordingly, the electric field being applied between the
transmissive portion and the counter electrode is different from
the electric field as applied between the reflective portion and
the counter electrode, resulting in creation of a difference
between the electric fields to be formed in the liquid crystal
layer in respective display modes. As a result, even when a counter
electrode voltage is an optimal voltage in the transmission mode,
it hardly becomes an optimal voltage for use in the reflection
mode.
[0031] In the liquid crystal display device as recited in the
paragraphs (1) to (8), which is arranged to perform image
displaying in both the transmission mode and the reflection mode
while using the same liquid crystal display panel, it is possible
to obtain an image display of high quality in either display mode
by switching the counter electrode voltage being applied to the
counter electrode between the transmission mode and the reflection
mode, to thereby establish the optimal counter electrode voltage in
a respective display mode.
[0032] Additionally, in the liquid crystal display device as
recited in the paragraph (9) and those that follow, optimal counter
electrode voltages are applied respectively to counter electrodes
which are provided on respective liquid crystal display panels used
for transmission mode display and reflection mode display. The
image signal lines are commonly used or "shared" by both liquid
crystal display panels and driven by image signal line drive
circuitry. The scan signal lines are formed into independent groups
on a per-panel basis. The scan signal lines are driven by
common-use scan signal drive circuitry.
[0033] The first liquid crystal display panel and second liquid
crystal display panel described above may be formed together on a
single panel in such a manner that each is within a divided area of
its own. Alternatively, each may be formed on a separate panel to
thereby provide separate liquid crystal display panels from the
point of view of their appearances. In the one with the
transmission mode display area and the reflection mode display area
provided on a single panel, display screens are on the same plane.
On the other hand, in the one with the transmission mode display
area and reflection mode display area on separate panels, it
becomes possible to dispose them on different faces of the
application equipment.
[0034] The counter electrode voltage switching (selection) may be
designed to be operatively responsive to turn-on and turn-off of
the backlight. With this scheme, during turn-on of the backlight, a
first counter voltage is selected to permit visual displaying of
images in the transmission mode; while, during turn-off of the
backlight, a second counter voltage is selected to establish image
display in the reflection mode. A control signal used to switch
between the counter electrode voltages may be output from a
main-body computer in accordance with the backlight's turn-on and
-off operations. Alternatively, specially provided switching means
may be used to enable manual switching therebetween.
[0035] With the above arrangements, it is possible to improve the
display image quality in each display mode of the
partial-transmissive/reflective liquid crystal display device with
provision of both the transmission mode displaying function and the
reflection mode display function. This in turn makes it possible to
obtain on-screen display images of high quality in either display
mode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 is a diagram schematically showing a plan view of a
first embodiment of the liquid crystal display device in accordance
with the present invention.
[0037] FIG. 2 is a circuit diagram of a single pixel in the liquid
crystal display device of FIG. 1.
[0038] FIG. 3 is a plan view diagram showing in greater detail the
configuration of the first embodiment of the liquid crystal display
device in accordance with this invention.
[0039] FIG. 4 is a diagram schematically showing a plan view of a
second embodiment of the liquid crystal display device in
accordance with the invention.
[0040] FIG. 5 is a plan view diagram showing one example of the
pixel configuration of a partial-transmissive/reflective liquid
crystal display device.
[0041] FIGS. 6A to 6C are cross-sectional diagrams of a main part
of the device shown in FIG. 5.
[0042] FIG. 7 is a plan view diagram showing an example of the
outer appearance of the liquid crystal display device in accordance
with the invention.
[0043] FIG. 8 depicts an exploded perspective view of a liquid
crystal display module using the liquid crystal display device in
accordance with the invention, as shown in FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] Practically implemented embodiments of the present invention
will be explained in detail with reference to the accompanying
drawings. Note that in the drawings to be referred to in the
following explanation, those elements having the same functions are
designated by the same reference characters, and a repetitive
explanation thereof will be omitted maximally as possible.
[0045] FIG. 1 illustrates a schematic plan view of a first
embodiment of the liquid crystal display device in accordance with
this invention. Reference character PNL as used in this drawing
indicates a liquid crystal display panel, wherein a liquid crystal
layer is interposed between a first substrate 1 and a second
substrate 503. This panel has on a main surface of the first
substrate 1--that is, on the inner face opposing the second
substrate--a plurality of scan signal lines (referred to as gate
lines hereinafter) GL which extend in a first direction (horizontal
direction as will be referred hereinafter as "x" direction) and are
provided in parallel with a second direction (vertical direction to
be referred to hereafter as "y" direction). The panel also has a
plurality of image/video signal lines (referred to as drain lines
hereafter) DL which extend in the y direction and are
parallel-provided in the x direction, while being disposed to cross
or intersect the gate lines GL.
[0046] Active elements are disposed at crossing points of the gate
lines GL and the drain lines DL. These active elements may
preferably be thin-film transistors TFT which control turn-on and
turn-off of pixels. FIG. 2 is a circuit diagram of a single pixel
in the liquid crystal display device of FIG. 1, wherein a thin-film
transistor TFT is connected at a cross point of a gate line GL and
a drain line DL. Selection of this thin-film transistor TFT causes
liquid crystal layers C.sub.L1, C.sub.L2 to be driven. Reference
character V.sub.com denotes a counter electrode voltage. The liquid
crystal layer C.sub.L1 is pictorially represented as a liquid
crystal layer that contributes to image display in a transmission
mode; while, the liquid crystal layer C.sub.L2 is as a liquid
crystal layer that contributes to display in a reflection mode.
This pixel arrangement is the same in the other embodiments, as
will be described later.
[0047] A display area 50 is arranged as a region in the form of a
two-dimensional matrix array in which thin-film transistors TFT are
connected to the cross points of the plurality of gate lines GL and
the plurality of drain lines DL. A scan signal line driving circuit
(referred to as gate driver hereinafter) 51, which drives the gate
lines GL, is mounted on the first substrate 1 along its one side
(right side edge of FIG. 1). An image signal line driving circuit
(referred to as drain driver hereafter) 52, which drives the drain
lines DL, is mounted on the first substrate 1 along another side
(lower side edge of FIG. 1). The drain driver 52 is equipped with a
counter voltage selector circuit 520, which distinguishes between
turn-on and turn-off of an illumination device and then applies a
counter voltage select signal to a counter voltage generating
circuit, as provided in a power supply circuit 53 to be described
later.
[0048] The counter voltage generation circuit is operatively
responsive to receipt of the counter voltage select signal for
applying a first counter voltage to a counter electrode, when the
illumination device turns on, and, when it turns off, for applying
a second counter voltage to the counter electrode. Note that
reference character JT indicates a terminal for power supply to the
counter electrode. This embodiment is a liquid crystal display
panel of the so-called twisted nematic (TN) type having the counter
electrode formed on a main surface of the second substrate 503.
And, a back-light unit is disposed on the back face of this liquid
crystal display panel PNL.
[0049] Electrode terminals (not shown) are formed at the end of the
above-noted one side of the first substrate 1. A flexible printed
circuit board 300 is provided which has its one end connected to
the electrode terminals and the other end connected to an external
signal source (not shown). Mounted on this flexible printed circuit
board 300 is a power supply circuit 53, which supplies a voltage(s)
required for producing a display to the liquid crystal display
panel PNL. Additionally, the power supply circuit 53 has a counter
voltage generation circuit. Display data is supplied from an
interface substrate (not shown) as an interface signal I/F, and
then it is converted by the drain driver 52 into a gradation or
color-tone signal adapted to image displaying, which will then be
supplied to a drain line(s) DL.
[0050] A source voltage V.sub.S for use as a drain driver power
supply voltage is supplied from the power supply circuit 53 to the
drain driver 52. A gate driver power supply voltage V.sub.G and a
gate control signal C.sub.G are supplied therefrom to the gate
driver 51. A power supply circuit control signal C.sub.P is
supplied from the drain driver 52 to the power supply circuit 53.
Based on this power supply circuit control signal C.sub.P, a
voltage and a control signal being supplied to the drain driver 52
are generated.
[0051] FIG. 3 is a diagram showing a plan view of the first
embodiment of the liquid crystal display device in accordance with
the invention, for more detailed explanation of its arrangement. As
seen in FIG. 3, the power supply circuit 53 of FIG. 1 has a first
counter voltage (V.sub.com1) generation circuit 531, a second
counter voltage (V.sub.com2) generation circuit 532, and a counter
voltage selector circuit 533. This selector circuit operates in
response to a power supply circuit control signal C.sub.P that is
output from the counter voltage selector circuit 520 included in
the drain driver 52, to thereby select one of the outputs
(V.sub.com1), (V.sub.com2) of the first counter voltage generation
circuit 531 and second counter voltage generation circuit 532. Any
one of the first counter voltage (V.sub.com1) and the second
counter voltage (V.sub.com2) which is selected by this counter
voltage selector circuit 533 is supplied to the power supply
terminal JT as the counter electrode voltage V.sub.C. The counter
voltage generation circuit as described has the first counter
voltage generation circuit 531, second counter voltage generation
circuit 532 and counter voltage selector circuit 533. The other
arrangements are the same as those in FIG. 1.
[0052] With such an arrangement, the power supply circuit 53
operates in response to the counter voltage select signal output
from the drain driver 52 based on turn-on and turn-off operations
of the backlight so as to apply to the counter electrode either the
first counter voltage optimized for the transmission mode when the
backlight turns on or the second counter voltage optimized for the
reflection mode when the backlight turns off. Thus, it is possible
to obtain high-quality on-screen display images that are free from
flicker or the like in a respective display mode.
[0053] FIG. 4 depicts a schematic plan view of a second embodiment
of the liquid crystal display device in accordance with the
invention, for explanation of its arrangement. This embodiment is
made up of a liquid crystal display panel PNL1 that is used to
display images in the transmission mode, and a liquid crystal
display panel PNL2 that is used for displaying in the reflection
mode. More specifically, the first liquid crystal display panel
PNL1 has a first liquid crystal layer which is interposed between
the main surface of a first substrate 1 and the main surface of a
second substrate 503, and it also has a number of gate lines GL-1
which extend in the x direction of the main surface of first
substrate 1 and are provided in parallel to the y direction, as
well as a number of drain lines DL-1 extending in the y direction
and being parallel-provided in the x direction, while intersecting
the gate lines GL-1.
[0054] The second liquid crystal display panel PNL2 has a second
liquid crystal layer which is sandwiched between the main surface
of a first substrate 1' and the main surface of a second substrate
503', and it also has a number of gate lines GL-2 which extend in
the x direction of the main surface of first substrate 1' and are
provided in parallel to the y direction; as well as a number of
drain lines DL-2 extending in the y direction and being
parallel-provided in the x direction, while crossing the gate lines
GL-2. A power supply circuit 53 is provided, for applying to a
counter electrode, that is provided on the first liquid crystal
display panel PNL1, either a first counter voltage (V.sub.com1)
optimized for the transmission mode or a second counter voltage
(V.sub.COM2) optimized for the reflection mode, as a counter
electrode voltage V.sub.C that is supplied to a power supply
terminal JT-1. The remaining arrangements are the same as those of
FIG. 3.
[0055] The power supply circuit 53 that is used in this embodiment
is equipped with a counter voltage selector circuit 534 for
selectively applying a counter electrode voltage to the power
supply terminal JT-1 of the counter electrode, as provided at the
first liquid crystal display panel PNL1, and a power supply
terminal JT-2 of the counter electrode, as provided at the second
liquid crystal display panel PNL2. The counter voltage selector
circuit 534 is operable in response to a power supply circuit
control signal C.sub.P which is output from the counter voltage
selector circuit 520 of the drain driver 52 to select one of the
outputs (V.sub.COM1), (V.sub.COM2) of the first counter voltage
generation circuit 531 and second counter voltage generation
circuit 532, and then apply a selected one to either the power
supply terminal JT-1 or the power supply terminal JT-2.
[0056] The liquid crystal display device with such an arrangement
is capable of using the first liquid crystal display panel PNL1 as
a main display panel, while the second liquid crystal display panel
PNL2 is used as a supplementary or auxiliary display panel, to
thereby mount them in electronic equipment. As an example, the
first liquid crystal display panel PNL1 is employable as a
communication information display screen of a mobile wireless
telephone handset, whereas the second liquid crystal display panel
PNL2 is usable as a display panel providing a lesser amount of
information, such as an incoming-call display window or the
like.
[0057] With the arrangement of this embodiment, in addition to the
effects and advantages obtainable by the arrangement of the
previous embodiment, it is possible for the power supply circuit 53
to establish a display in the transmission mode, while the
backlight turns on during communication operations using the first
liquid crystal display panel PNL1, and alternatively to establish a
display in the reflection mode when the backlight turns off during
non-communication operations, such as call-waiting events or the
like, thereby enabling achievement of selective use of respective
features.
[0058] Optionally, it is also possible to form the first liquid
crystal display panel PNL1 and the second liquid crystal display
panel PNL2, as described with reference to FIG. 4, on the same
substrate, to thereby permit usage in an independent form for
performing "two-in-one" display operations on the same plane with a
portion of the main display area serving as a sub-display area.
[0059] Although the selection between the transmission mode and
reflection mode in each of the above-noted embodiments is carried
out such that the counter voltage selector circuit 520 provided in
the drain driver 52 automatically judges based on the backlight
turn-on/off signal, as stated above, it may also be arranged so
that a changeover switch or an operation unit of a variable
resistor is provided in the application equipment, thereby enabling
manual switching or free adjustment of the counter electrode
voltage value(s) on a case-by-case basis.
[0060] Next, an explanation will be given of one example of the
pixel configuration of a display panel which makes up a
partial-transmissive/reflective liquid crystal display device,
which is the liquid crystal display device of the invention.
[0061] FIG. 5 is a plan view diagram of one example of the pixel
configuration of the partial-transmissive/reflective liquid crystal
display device, and FIGS. 6A to 6C are diagrams each showing a
cross-sectional view of main part of FIG. 6. Note here that FIG. 5
shows a planar configuration of four adjacent pixels. FIGS. 6A-6C
show cross-sections as taken along lines A-A', B-B' and C-C' of
FIG. 5, respectively. Also note that FIG. 5 and FIGS. 6A-6C show
only one substrate side on which active elements (for example,
thin-film transistors) are formed for performing pixel selection,
wherein any illustration of the other substrate with more than one
color filter and counter electrode provided thereon is omitted.
[0062] In FIG. 5 and FIGS. 6A-6C, a pixel structure body is formed
on or above a buffer film which overlies a nonalkali glass
substrate 1, and it is comprised of a Si.sub.3N.sub.4 film 200
having a thickness of 50 nanometers (nm) and a SiO.sub.2 film 2
with a thickness of 120 nm. Formed on this buffer film is a
polycrystalline silicon (poly-Si) film 30 with a thickness of 50
nm, which constitutes thin-film transistors TFT. Gate lines 10
(corresponding to GL in FIGS. 1-4) made of Mo with a thickness of
200 nm are formed over the poly-Si film 30, with a 100-nm thick
SiO.sub.2 gate dielectric film 20 sandwiched therebetween.
[0063] And, a common electrode 11 for charge accumulation is formed
by using the same Mo as the gate lines 10. This common electrode 11
is indicated by dotted contour lines in FIG. 5. An interlayer
dielectric film 21 made of SiO.sub.2 with a thickness of 10 nm is
formed to overlie and cover the common electrode 11. Drain lines 12
(corresponding to DL in FIGS. 1-4) comprised of a three-layer
metallic film of a Mo layer 12a and an Al layer 12b, plus a Mo
layer 12c and a reflective electrode 13, which also acts as source
electrodes of the thin-film transistors, are connected by way of
contact through-holes TH1, TH2 that are provided in the interlayer
dielectric film 21.
[0064] Of the three-layer metal film of the Mo layer 13a and Al
layer 13b, plus the Mo layer 13c, making up this reflective
electrode 13, the Mo layer 13a that underlies the Al layer 13b is
provided for reduction of the contact resistance between the Si
film 30 and Al layer 13b. Similarly, the Mo layer 13c is provided
to reduce the resistance between it and pixel electrodes 14. In
FIG. 6A, two gate electrodes 10 are formed above the Si film 30.
One of these two gate electrodes 10 is the so-called main line
which extends along a plurality of pixel regions provided in
parallel. The other of them is a branch line which is projected or
protruded from this main line toward one certain pixel region (see
FIG. 5).
[0065] Of the reflective electrode 13 portion which serves also for
use as a source electrode 15, the Mo film 13c at an upper layer
level is left only at a contact portion with an ITO film making up
the pixel electrode 14 and its peripheral portions, and the Mo film
of the upper layer is removed away at the remaining portions. The
main surface of a thin-film transistor substrate is covered or
coated with both a protective dielectric film 22 made of
Si.sub.3N.sub.4 with a thickness of 200 nm and an organic
protective film 23 mainly comprised of acrylic resin material with
a thickness of 2 micrometers (.mu.m). A pixel electrode 14 made of
ITO is connected to the source electrode 15 (reflective electrode
13) of a thin-film transistor via a contact through-hole TH3, which
is provided in the protective dielectric film 22 and the organic
dielectric film 23. A charge accumulation capacitive element is
formed by the reflective electrode 13 and the common electrode 11
of the charge accumulation capacitance, having the interlayer
dielectric film 21 sandwiched therebetween.
[0066] Since the pixel electrode 14 is provided on the upper side
(i.e. liquid crystal side not shown) of the reflective electrode
13, it is possible for the reflective electrode 13 to offer the
functionality for control of the orientation or alignment
directions of liquid crystal molecules in the liquid crystal layer
even in the so-called reflective display area. With such an
arrangement, it is possible to provide the intended
partial-transmissive/reflective liquid crystal display device with
increased aperture ratios and enhanced brightness or
luminosity.
[0067] FIG. 7 is a plan view showing an example of the outer
appearance of the liquid crystal display device in accordance with
the invention. The first substrate 1 and second substrate 503 make
up a liquid crystal display panel having an active-matrix array
(display area) 50, with a scan signal line drive circuit 51 and
image signal line drive circuit 52 mounted at peripheral portions
thereof. These circuits are formed of integrated circuit chips. A
power supply circuit 53 is mounted on a flexible printed circuit
board 300.
[0068] FIG. 8 is an exploded perspective view of the liquid crystal
display module using the liquid crystal display device in
accordance with the invention as shown in FIG. 7. This LCD module
has on the first substrate 1 an active-matrix array (display area)
50 along with a scan signal line drive circuit 51 and image signal
line drive circuit 52, with a color filter CF and counter electrode
(not shown) formed on or above the main surface (inner surface) of
a second substrate 503. A liquid crystal layer is sealed between
the first substrate 1 and the second substrate 503. Further, a
phase difference film 504 and an optical polarization film 505 are
provided on or above the back face of the first substrate 1.
Similarly, a phase difference film 509 and a polarization film 501
are provided on or above the back surface of the second substrate
503 also.
[0069] The scan signal line drive circuit 51 and the image signal
line drive circuit 52 are mounted at the periphery of the first
substrate 1. One end of the flexible printed circuit board 300, on
which the power supply circuit 53 that is made up of more than one
integrated circuit chip is mounted, is connected to a mount side
edge of the image signal line drive circuit 52. Terminals 301 at
the other end are connected to an external signal source (not
shown). An illumination device (backlight), which is constituted
from a light-emitting diode 506 and a light guide plate 507, is
disposed on the back face of the liquid crystal display panel.
These constituent components are made integral by a lower case 508
and an upper case 500, to thereby complete the liquid crystal
display module. This liquid crystal display module is designed for
use as the display means in cellular telephone handsets and/or
mobile information terminals, such as palmtop computers and
personal digital assistant (FDA) tools.
[0070] As apparent from the foregoing description, according to the
present invention, it is possible to improve the display quality in
each display mode in a partial-transmissive/reflective liquid
crystal display device having both a transmission mode displaying
function and a reflection mode display function, thereby enabling
achievement of a liquid crystal display device that is capable of
performing high-quality image/video displaying operations in either
display mode.
* * * * *