U.S. patent application number 14/306307 was filed with the patent office on 2014-10-02 for display device and an electronic apparatus using the same.
The applicant listed for this patent is Semiconductor Energy Laboratory Co., Ltd.. Invention is credited to Jun Koyama, Shunpei Yamazaki.
Application Number | 20140292618 14/306307 |
Document ID | / |
Family ID | 32871252 |
Filed Date | 2014-10-02 |
United States Patent
Application |
20140292618 |
Kind Code |
A1 |
Yamazaki; Shunpei ; et
al. |
October 2, 2014 |
DISPLAY DEVICE AND AN ELECTRONIC APPARATUS USING THE SAME
Abstract
In a conventional, display device comprising a sub-display, the
display device is increased in thickness and in the number of
components as the number of displays is increased. In the present
invention, a dual emission display device is used so that either
surface of a display is used as a main display or a sub-display.
Accordingly, the display device can be reduced in thickness and in
the number of components. Further, mechanical reliability can be
enhanced when the invention is applied to a tablet PC, a video
camera and the like.
Inventors: |
Yamazaki; Shunpei; (Tokyo,
JP) ; Koyama; Jun; (Sagamihara, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Semiconductor Energy Laboratory Co., Ltd. |
Atsugi-shi |
|
JP |
|
|
Family ID: |
32871252 |
Appl. No.: |
14/306307 |
Filed: |
June 17, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13707647 |
Dec 7, 2012 |
8760375 |
|
|
14306307 |
|
|
|
|
13189852 |
Jul 25, 2011 |
8330670 |
|
|
13707647 |
|
|
|
|
11969232 |
Jan 4, 2008 |
8009145 |
|
|
13189852 |
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|
10799756 |
Mar 15, 2004 |
7327335 |
|
|
11969232 |
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Current U.S.
Class: |
345/1.2 |
Current CPC
Class: |
G06F 3/1423 20130101;
H01L 27/14678 20130101; G09G 2300/0842 20130101; G09G 2340/0492
20130101; G09G 3/3258 20130101; G09G 5/393 20130101; G09G 2300/023
20130101; H01L 27/3244 20130101; G09G 2310/0251 20130101; H01L
27/3269 20130101; G09G 2360/142 20130101; G09G 5/395 20130101; G09G
3/3266 20130101; G09G 2360/14 20130101; H01L 2251/5323 20130101;
F21V 21/00 20130101; G09G 3/2022 20130101; F21V 9/14 20130101; G09G
3/30 20130101 |
Class at
Publication: |
345/1.2 |
International
Class: |
G06F 3/14 20060101
G06F003/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 9, 2003 |
JP |
2003-105923 |
Apr 11, 2003 |
JP |
2003-108484 |
Claims
1. A display device comprising: light emitting elements formed over
a light transmissive substrate; a first display surface over one
surface of the light transmissive substrate; and a second display
surface over the other surface of the light transmissive substrate,
wherein an image is displayed on a first display screen formed on
the first display surface and a second display screen formed on the
second display surface using a light from the light emitting
elements, and wherein the first display screen is larger than the
second display screen.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 13/707,647, filed Dec. 7, 2012, now allowed, which is a
divisional of U.S. application Ser. No. 13/189,852, filed Jul. 25,
2011, now U.S. Pat. No. 8,330,670, which is a divisional of U.S.
application Ser. No. 11/969,232, filed Jan. 4, 2008, now U.S. Pat.
No. 8,009,145, which is a divisional of U.S. application Ser. No.
10/799,756, filed Mar. 15, 2004, now U.S. Pat. No. 7,327,335, which
claims the benefit of foreign priority applications filed in Japan
as Serial No. 2003-105923 on Apr. 9, 2003, and Serial No.
2003-108484 on Apr. 11, 2003, all of which are incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a display device having a
display screen which is formed on a flat plate surface by using a
light emitting element typified by an electro luminescence element,
and more particularly relates to an electronic apparatus using the
display device.
[0004] 2. Description of Related Art
[0005] In recent years, with the development in communication
technologies, portable telephone sets have been widely used: In
future, transmission of moving pictures and transmission of a large
volume of information are expected. On the other hand, through
reduction in weight of personal computers (PCs), those adapted for
mobile communication have been produced. Information terminals
called PDA originated in electronic notebooks have also been
produced in large quantities and widely used. In addition, with the
advance of display devices, most of those portable information
apparatuses are equipped with a flat panel display.
[0006] Among active matrix display devices, manufacturing of a
display device by the use of low temperature poly-silicon thin film
transistors (referred to as TFTs hereinafter) is promoted. The use
of low temperature poly-silicon TFTs has advantages in that in
addition to manufacturing of a pixel, a signal line driver circuit
can be integrally formed around a pixel portion in a display
device. Thus, it is possible to realize miniaturization and high
definition of a display device, and such a display device is
expected to be more widely used in future.
[0007] For portable PCs, tablet PCs have been developed. As shown
in FIGS. 2A and 2B, a tablet PC comprises a first housing 201, a
second housing 202, a keyboard 203, a touch pad 204, a display
portion 205 including a touch sensor, an axis of rotation 206, and
a touch pen 207. When using the keyboard 203 in such a tablet PC,
as shown in FIG. 2A, data can be input with the keyboard 203 while
looking at the display as in other notebook PCs. Meanwhile, when
characters and data are input without using the keyboard 203, as
shown in FIG. 2B, the display portion 205 including a touch sensor
and the touch pen 207 are used by rotating the first housing 201 in
a complicated way and covering the keyboard 203 with the first
housing 201.
[0008] As for portable telephone sets, bar-type phones have been
replaced by flip phones, and among flip phones, those having two
displays have been actively developed. FIGS. 3A, 3B and 3C show an
internal side, an external side and a lateral side of a flip phone,
respectively. The flip phone shown in FIGS. 3A to 3C comprises a
first housing 301, a second housing 302, a first display portion
303, a second display portion 304, a speaker 306, an antenna 307, a
hinge 308, a keyboard 309, a microphone 310, and a battery 311. As
shown in FIGS. 3A to 3C, a sub-display (the second display portion
304) is provided as well as a main display (the first display
portion 303), and thus the time, a battery charge status, a message
reception status and the like can be displayed on the sub-display
instead of on the main display (see Japanese Laid-Open Patent
Application No. 2001-285445, for example).
SUMMARY OF THE INVENTION
[0009] In the above-described conventional, tablet PC, the first
housing is required to be rotated around the axis of rotation in a
complicated way in order to use one display portion in different
positions. Therefore, mechanical reliability of the tablet PC is
lowered as compared with a PC using a simple hinge, thus machine
life is shortened.
[0010] In the above-described portable telephone set comprising
both a main display and a sub-display, control circuits for
controlling each of the displays are necessarily provided, leading
to the increase in the number of components, and the increase in
volume and cost of the portable telephone set. Further, the two
displays make the first housing thicker and also increase the
volume of the portable telephone set.
[0011] In view of the foregoing, it is a general object of the
invention to provide a display device having two displays while
reducing the number of components and volume and improving
mechanical reliability. It is another object of the invention to
provide an electronic apparatus using such a display device.
[0012] To solve the above-described problems, according to the
invention, a dual emission display is used, which serves as both a
main display and a sub-display. The dual emission display allows an
electronic apparatus to have a high reliability without using a
complicated axis of rotation.
[0013] A display device according to the invention comprises a
light emitting element formed over a light transmissive substrate,
wherein light from the light emitting element is emitted to the
light transmissive substrate side and to the opposite side thereof
so as to form a first display surface and a second display surface,
and a first display screen formed on the first display surface is
as large as a second display screen formed on the second display
surface.
[0014] A display device according to the invention comprises a
light emitting element formed over a light transmissive, substrate,
wherein light from the light emitting element is emitted to the
light transmissive substrate side and to the opposite side thereof
so as to form a first display surface and a second display surface,
and a first display screen formed on the first display surface is
larger than a second display screen formed on the second display
surface.
[0015] A display device according to the invention comprises a
light emitting element formed over a light transmissive substrate,
wherein light from the light emitting element is emitted to the
light transmissive substrate side and to the opposite side thereof
so as to form a first display surface and a second display surface,
and a plurality of display screens are formed on either the first
display surface or the second display surface.
[0016] In the above-described display device according to the
invention, the light emitting element may emit white light and a
color filter may be provided on the side of the first display surf
ace.
[0017] In the above-described display device according to the
invention, the first display surface and the second display surface
may be formed of a plurality of light emitting elements having
different emission colors.
[0018] In the above-described display device according to the
invention, the scan direction of the first display screen may be
different from that of the second display screen.
[0019] In the above-described display device according to the
invention, the first display screen and the second display screen
may comprise a signal line driver circuit in common and the signal
line driver circuit may have a switching means for changing the
scan direction.
[0020] The above-described display device according to the
invention may comprise a volatile storage means and a switching
means for changing the reading order of data stored in the volatile
storage means.
[0021] In the above-described display device according to the
invention, the first display surface and the second display surface
may be sandwiched between at least two polarizers having different
polarization directions.
[0022] The above-described display device according to the
invention may comprise a signal line driver circuit capable of
arbitrarily selecting a signal line from a plurality of signal
lines extending on the first display screen and the second display
screen, and capable of outputting an image signal to the signal
line.
[0023] In the above-described display device according to the
invention, a photoelectric converter is provided on either or both
of the first display screen and the second display screen.
[0024] An electronic apparatus according to the invention comprises
a light emitting element formed on a light transmissive substrate,
a first housing and a second housing which are connected to each
other so as to be used both in open position and closed position, a
display means mounted in the first housing, which emits light from
the light emitting element to the light transmissive substrate side
and the opposite side thereof so as to form a first display surface
and a second display surface, a detecting means for detecting a
signal corresponding to the angle between the first housing and the
second housing, and a switching means for changing the scan
direction of the display means in accordance with a signal output
from the detecting means.
[0025] An electronic apparatus according to the invention comprises
a light emitting element formed on a light transmissive substrate,
and a display means for emitting light from the light emitting
element to the light transmissive substrate side and the opposite
side thereof so as to form a first display surface and a second
display surface, wherein a first display screen formed on the first
display surface is as large as a second display screen formed on
the second display surface.
[0026] An electronic apparatus according to the invention comprises
a light emitting element formed on a light transmissive substrate,
and a display means for emitting light from the light emitting
element to the light transmissive substrate side and the opposite
side thereof so as to form a first display surface and a second
display surface, wherein a plurality of display screens are formed
on either the first display surface or the second display
surface.
[0027] An electronic apparatus according to the invention includes
a personal computer, a video camera, a digital camera, a portable
communication tool and the like each of which comprises a display
screen.
[0028] An electronic apparatus according to the invention may
comprise an electrical storage means and a light emission control
means for lighting a display screen when the electrical storage
means is charged.
[0029] The above-described light emission control means may be
added with a function for lighting or flashing a display screen or
an inverted display screen whose contrast is inverted from that of
a normal display screen, or a function for lighting a pixel which
is less in deterioration. That is, this light emission control
means may be added with a recording medium on which is recorded a
control program for lighting or flashing a display screen, a
recording medium on which is recorded a control program for
lighting or flashing an inverted display screen whose contrast is
inverted from that of a normal display screen, or a recording
medium on which is recorded a control program for lighting a pixel
which is less in deterioration.
[0030] In a conventional portable telephone set having a
sub-display, the two displays inhibit reduction in volume and cost
of the portable telephone set. Meanwhile, in a conventional tablet
PC, the use of one display rotated in a complicated way causes a
low mechanical reliability.
[0031] According to the invention, a dual emission display
functions as a plurality of displays and thus an electronic
apparatus which is reduced in volume and cost and exhibits an
improved mechanical reliability can be achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1A is a front elevational view of an embodiment mode of
the invention.
[0033] FIG. 1B is a rear elevational view of the embodiment mode of
the invention.
[0034] FIG. 1C is a side elevational view of the embodiment mode of
the invention.
[0035] FIG. 2A shows a conventional tablet PC in open position.
[0036] FIG. 2B shows the conventional tablet PC in closed
position.
[0037] FIG. 3A shows an internal side of a conventional portable
telephone set.
[0038] FIG. 3B shows an external side of the conventional portable
telephone set.
[0039] FIG. 3C shows a lateral side of the conventional portable
telephone set.
[0040] FIG. 4A shows a tablet PC of the invention in open
position.
[0041] FIG. 4B shows the tablet PC of the invention in closed
position.
[0042] FIG. 5A shows an internal side of a portable telephone set
of the invention.
[0043] FIG. 5B shows an external side of the portable telephone set
of the invention.
[0044] FIG. 5C shows a lateral side of the portable telephone set
of the invention.
[0045] FIG. 6 is a circuit diagram of a source signal line driver
circuit.
[0046] FIG. 7 is a circuit diagram of a gate signal line driver
circuit with a decoder.
[0047] FIGS. 8A and 8B show a display panel with a built-in
sensor.
[0048] FIG. 9 is a block diagram of a display controller.
[0049] FIGS. 10A and 10B show an embodiment of a dual emission
display device.
[0050] FIGS. 11A and 11B show a video camera using the
invention.
[0051] FIGS. 12A to 12D show a digital camera using the
invention.
[0052] FIGS. 13A and 13B show a wristwatch communication tool using
the invention.
[0053] FIG. 14 is a block diagram of an electronic apparatus using
the invention.
[0054] FIG. 15A shows a pixel of an active matrix light emitting
device.
[0055] FIG. 15B is a timing chart of the same.
[0056] FIG. 16A shows a pixel of an active matrix light emitting
device.
[0057] FIG. 16B is a timing chart of the same.
[0058] FIGS. 17A to 17C show an embodiment mode of the invention in
the case of using polarizers.
[0059] FIG. 18 is a schematic diagram of a dual emission display
device.
[0060] FIG. 19 shows a pixel of a display device of the
invention.
[0061] FIG. 20 is a block diagram of an electronic apparatus using
the invention.
[0062] FIG. 21 is a block diagram of a display controller:
[0063] FIG. 22 shows an electronic apparatus using the invention
during charging.
[0064] FIG. 23 shows an example of a pixel circuit using the
invention.
[0065] FIG. 24 shows a dual emission display panel using the
invention.
DETAILED DESCRIPTION OF THE INVENTION
Embodiment Mode
[0066] Although the present invention will be fully described by
way of example with reference to the accompanying drawings, it is
to be understood that various changes and modifications will be
apparent to those skilled in the art. Therefore, unless otherwise
such changes and modifications depart from the scope of the
invention hereinafter defined, they should be constructed as being
included therein.
[0067] With reference to FIGS. 1A to 1C, Embodiment Mode of the
invention will be described hereinafter. FIG. 1A is a view of a
display device according to the invention, seen from a first
display surface, FIG. 1B is a view of the same seen from a second
display surface, and FIG. 1C is a side elevational view of the
display device according to the invention. In FIGS. 1A to 1C, the
display device of the invention comprises light transmissive
substrates 101 and 102, and display screens 105 to 108. A display
screen 105 is provided on the first display surface, and display
screens 106 to 108 are provided on the second display surface.
Driver circuits 103 and 104 for driving the display screens 105 to
108 are made up of TFTs and provided on the light transmissive
substrate 101. An image signal and a control signal are input to
the driver circuits 103 and 104 through FPCs (Flexible Printed
Circuits) 109 and 110 each connected to the light transmissive
substrate 101, and thereby drive the display screens 105 to
108.
[0068] The display screen 105 on the first display surface displays
an image by using substantially the whole of the first display
surface. Meanwhile, the display screens 106 to 108 on the second
display surface occupy a part of the second display surface to
display an image. Accordingly, the display screen 105 can be used
as a main display and the display screens 106 to 108 can be used as
sub-displays. In FIG. 1B, a received e-mail, the reception status
of the radio wave, and the time are displayed on the display
screens. 106, 107, and 108 respectively. However, displayed content
is not limited to these and other content can be displayed.
Further, the number of sub-display screens is not limited to three
as shown in FIG. 1B, and one or more display screens can be
provided arbitrarily.
[0069] As for a part of the second display surface, on which no
image is displayed, a black display may be kept on or a black
matrix may be provided on this part, or the part may be covered
with a material of the housing when the display device is put in
the housing.
[0070] It is to be noted that the number, the form and the size of
sub-display screens are not limited to examples shown in FIG. 1B,
and can be determined arbitrarily. The emission color of the main
display screen can also be selected arbitrarily. For example, when
a white light emitting element is used for a Light emitting element
of the display device, a full color display may be performed on the
main display screen by using color filters, and a white display may
be performed on the sub-display screens without using color
filters. Alternatively, a light emitting element including a
plurality of emission colors may be used.
[0071] The display device according to the invention described
above has a built-in driver circuit, though the driver circuit is
not necessarily implemented in the display device. An LSI may be
bonded with TAB or a chip may be attached directly on a light
transmissive substrate. Also, the display portion is not limited to
an active matrix type using poly-silicon TFTs, and an active matrix
type using amorphous TFTs or a passive matrix type may also be
used.
[0072] FIG. 18 is a schematic diagram of a dual emission display
device according to the invention. In FIG. 18, the display device
comprises light transmissive substrates 1801 and 1802, and
transparent or quasi-transparent electrodes 1803 to 1805 and 1809
interposed between the two substrates. Light emitting elements 1806
to 1808 are sandwiched between the electrodes 1803 to 1805 and
1809. On a surface of the light transmissive substrate 1801, color
filters 1810 to 1812 are disposed. When the light emitting elements
1806 to 1808 emit a white light, a full color display can be
performed on the first light emitting surface and a white display
can be performed on the second light emitting surface. The color
filters are not necessarily provided and the light emitting
elements 1806 to 1808 may include a plurality of emission colors.
In the latter case, the same color is displayed on each of the
first light emitting surface and the second light emitting surface.
For the light emitting elements 1806 to 1808, light emitting
elements typified by electro luminescence (EL) elements are used.
According to such a structure, the dual emission display device can
be achieved.
[0073] With reference to FIGS. 4A and 4B, an embodiment mode of the
invention, which is applied to a tablet PC, will be described. The
tablet PC shown in FIGS. 4A and 4B comprises a first housing 401, a
second housing 402, hinges 409 and 410 for connecting the first
housing 401 with the second housing 402, a keyboard 403, a touch
pad 404, a main display screen 405, sub-display screens 406 to 408,
and a touch pen 411. Since the sub-display screen 406 includes a
touch sensor as described in the related art, users can enjoy the
advantage of the tablet PC by using the touch pen 411.
[0074] In the conventional tablet PC described in the related art,
the display device comprises only one display portion and the
housing is rotated around the axis of rotation in order to use the
display portion for both a main display and a tablet display. In
the embodiment mode shown in FIGS. 4A and 4B, however, the
complicated axis of rotation described in the related art is
dispensed with by using the display device of the invention shown
in FIGS. 1A to 1C, and only the hinges 409 and 410 are required.
According to such a structure, the mechanical reliability which is
acknowledged as a problem in the conventional tablet PC can be
enhanced.
[0075] FIGS. 5A to 5C shows an embodiment mode of a portable
telephone set using the display device of the invention. The
portable telephone set shown in FIGS. 5A to 5C comprises a first
housing 501, a second housing 502, a first display screen 503, a
second display screen 504, a third display screen 505, a speaker
506, an antenna 507, a hinge 508, a keyboard 509, a microphone 510,
and a battery 511. FIGS. 5A, 5B, and 5C show an internal side, an
external side, and a lateral side of the portable telephone set,
respectively. The display device of the invention is mounted in the
first housing 501. Accordingly, the first housing 501 of the
display device according to the invention can be reduced in
thickness as compared with that of the conventional portable
telephone set shown in the related art, in which the two display
devices are mounted.
[0076] The number of sub-display screens is not limited to two as
shown in FIG. 5B, and one or three or more sub-display screens may
be used.
[0077] Although the tablet PC and the portable telephone set are
described in this embodiment mode, the invention is not exclusively
applied to these, and can be applied to electronic apparatuses
using various display devices, such as a PDA, a video camera, a
digital camera, a portable DVD (Digital Versatile Disc), a portable
TV, and a game machine.
Embodiment 1
[0078] With reference to FIG. 6, explanation will be made on a
source signal line driver circuit used for the display devices of
the invention. Since images are displayed on both sides of the
display device in the invention, the images are displayed in
opposite directions viewing from the opposite side. Therefore, the
driving direction of the screen has to be changed depending on the
direction from which the screen is viewed. Thus, in the display
device of the invention, a source signal line driver circuit is
formed as shown in FIG. 6.
[0079] A source signal line driver circuit shown in FIG. 6
comprises a shift register 601, a NAND circuit 607, a buffer
circuit 608, and analog switches 609 to 612. The operation is
explained hereinafter. The shift register 601 is formed with a
series of DFFs 602, each of which comprises clocked inverters 603
and 604 and an inverter 605. A signal is input to the DFF 602 from
a terminal SSP and transferred to the subsequent DFF 602 by clock
signals (CL and CLK). A switch 606 is controlled by a SL/R to
select whether to transfer a pulse to the precedent stage or to the
subsequent stage. When the precedent stage is selected by the
switch 606, a pulse is transferred from left to right, and when the
subsequent stage is selected, a pulse is transferred from right to
left.
[0080] These pulses are transferred to the NAND circuit 607 and
then to the buffer circuit 608 to drive the analog switches 609 to
612. Image signals are sampled through the analog switches 609 to
612 and transferred to source signal lines S1 to S4.
[0081] In this manner, the switch 606 enables the image direction
to change to the left or right, and the source signal line driver
circuit can be applied to the dual emission display device of the
invention. It is to be noted that such driver circuit may be formed
on a light transmissive substrate by using TFTs, an LSI may be
bonded with TAB, or an LSI may be attached directly on a light
transmissive substrate.
Embodiment 2
[0082] FIGS. 15A and 15B show an example of a light emitting
display device using time gray scale. FIG. 15A shows a pixel for
driving a light emitting element 1503 by using time gray scale. The
pixel comprises a driving TFT 1502, a storage capacitor 1505 and a
switching TFT 1501 as well as the light emitting element 1503. A
gate of the switching TFT 1501 is connected to a gate signal line
G1. When the gate signal line G1 is high, the switching TFT 1501 is
turned ON and data on a source signal line S1 is written to the
storage capacitor 1505 and a gate of the driving TFT 1502. When the
driving TFT 1502 is turned ON, a current is supplied from a power
supply line V1 to the light emitting element 1503 through the
driving TFT 1502. This state is held until the next writing is
done.
[0083] FIG. 15B is a timing chart of time gray scale. In this
embodiment, 4-bit time gray scale is taken as an example, though
the invention is not exclusively limited to 4-bit. One frame is
composed of four sub-frames SF1 to SF4. The sub-frames SF1 to SF4
each include address periods (writing periods) Ta1 to Ta4, and
sustain periods (lighting periods) Ts1 to Ts4, respectively. When
the ratio between the sustain periods Ts1:Ts2:Ts3:Ts4 is set equal
to 8:4:2:1, each bit corresponds to each sustain period, thus time
gray scale can be achieved. The address periods emit no light at
this time, and perform only writing.
[0084] In order to drive the display device by using such time gray
scale, a display controller and a memory are required for
generating sub-frames. The display controller and the memory also
enable to change the image direction to the left and right. FIG. 9
shows a display controller and a memory. In this example a 4-bit
digital video signal is divided into sub-frames, though the
invention is not exclusively limited to the 4-bit signal. The
operation will be described hereinafter. First; a display
controller 902 inputs a digital video signal to a memory A 904
through a switch 903. After all the data in the first frame is
input to the memory A 904, the switch 903 is switched to a memory B
905 to write a digital video signal in the second frame.
[0085] On the other hand, a switch 906 is sequentially connected to
memories A 904-1 to 904-4, and the signal stored in the memory A
904 is input to a display 901. After all the data in the second
frame is input to the memory B 905, the switch 903 is switched to
the memory A 904 to write a digital video signal in the third
frame. Meanwhile, the switch 906 is sequentially connected to
memories B 905-1 to 905-4, and the signal stored in the memory B
905 is input to the display 901. By repeating such an operation,
sub-frames can be generated.
[0086] In the case where an image direction, is changed to the left
and right, signals are reversely called up per column of a display
when the memory A 904 or the memory B 905 is called up. In this
manner, in the display device in which sub-frames are generated,
dual emission can be achieved by changing the order of calling up
the memory.
Embodiment 3
[0087] FIGS. 16A and 16B show an example of a light emitting
display device using time gray scale. FIG. 16A shows a pixel for
driving a light emitting element 1603 by using time gray scale. The
pixel comprises a driving TFT 1602, an erasing TFT 1606, a storage
capacitor 1605 and a switching TFT 1601 as well as the light
emitting element 1603. A gate of the switching TFT 1601 is
connected to a gate signal line G1. When the gate signal line G1 is
high, the switching TFT 1601 is turned ON, and data on a source
signal line S1 is written to the storage capacitor 1605 and a gate
of the driving TFT 1602. When the driving TFT 1602 is turned ON, a
current is supplied from a power supply line V1 to the light
emitting element 1603 through the driving TFT 1602. This state is
held until the next writing is done.
[0088] FIG. 16B is a timing chart of time gray scale. In this
embodiment, 4-bit time gray scale is taken as an example, though
the invention is not exclusively limited to 4-bit. One frame is
composed of four sub-frames SF1 to SF4. The sub-frames include
address periods (writing periods) Ta1 to Ta4, sustain periods
(lighting periods) Ts1 to Ts4, and an erase period Te. When the
ratio between the sustain periods Ts1:Ts2:Ts3:Ts4 is set equal to
8:4:2:1, each bit corresponds to each of the sustain periods, thus
time gray scale can be achieved. By providing the erase period Te
in this pixel, it is possible to use time effectively. Light can be
emitted in the address periods in the example shown in FIGS. 16A
and 16B, though it is not possible in the example shown in FIGS.
15A and 15B. The erase period Te is required in the case where the
lighting period is shorter than the address period. Thus, an
erasing TFT 1606 and an erase line E1 are added for erasing in the
pixel in FIG. 16A.
[0089] As in Embodiment 2, the image direction can be, changed to
the left and right by changing the order of calling up the memory
circuit.
[0090] FIG. 19 shows an example of a pixel which is different from
that in FIG. 16A. FIG. 19 shows a pixel for driving a light
emitting element 1903 by using time gray scale. The pixel comprises
a driving TFT 1907, an erasing TFT 1906, a storage capacitor 1905
and switching TFTs 1901 and 1902 as well as the light emitting
element 1903. A gate of the switching TFT 1901 is connected to a
gate signal line G1. When the gate signal line G1 is high, the TFT
1901 is turned ON, and data on a source signal line S1 is written
to the storage capacitor 1905 and a gate of the switching TFT 1902.
When the switching TFT 1902 is turned ON, a current is supplied
from a power supply line V1 to the light emitting element 1903
through the switching TFT 1902 and the driving TFT 1907. This state
is held until the next writing is done. A gate of the driving TFT
1907 is connected to a power supply line V2 which has a fixed
potential. When the switching TFT 1902 is turned ON, a current
corresponding to a potential difference between the V1 and the V2
is supplied to the light emitting element 1903. Such a pixel is
suitable for constant current drive in which the driving TFT 1907
is used in a saturation region.
Embodiment 4
[0091] FIG. 7 shows an example of a gate signal line driver circuit
using a decoder. The decoder inputs address signals from address
lines 1, 1b, 2, 2b, 3, 3b, 4, and 4b to NAND circuits 701 and 702,
and outputs the address signals to a gate signal line G001 through
a NOR circuit 703 and inverters 704 and 705. In the above-described
shift register, a signal line can not be selected arbitrarily
because pulses are sequentially shifted, while in the decoder, a
signal line can be selected arbitrarily by performing addressing.
Accordingly, by using the decoder, the display screen shown in
Embodiment Mode can be lighted partially, and the lighted part can
be used for a sub-display.
Embodiment 5
[0092] FIGS. 13A and 13B show a wristwatch communication tool using
the invention. FIG. 13A is the wristwatch communication tool in
closed position and FIG. 13B is the same in open position.
Reference numeral 1301 denotes a first housing and 1302 denotes a
second housing. The display device of the invention is mounted in
the second housing 1302. Reference numerals 1303 and 1304 denote
belts, 1305 denotes a first display surface, 1306 denotes a second
display surface, 1307 denotes a camera, 1308 denotes a keyboard,
1309 denote's a microphone, and 1310 denotes a speaker.
[0093] In the case of using the communication tool in closed
position, the time is displayed on the first display surface 1305,
and the communication tool can be used as a common wristwatch. When
using it in open position, various images can be displayed on the
second display surface 1306. When the communication tool has the
videophone function, for example, it is possible to display the
face of the person at the other end of the line. Alternatively, the
second display surface 1306 can be used as a Web terminal by
accessing to the Internet. Also, other software applications or TV
programs can be displayed on it. The first display surface 1305 may
display a message reception status or a battery charge status as
well as the time.
Embodiment 6
[0094] FIGS. 11A and 11B show a video camera using the invention.
Generally in a video camera, a liquid crystal display is used for a
monitor. When a videographer records a video image of others or
objects, a monitor has to be turned to the opposite direction of a
camera lens. On the other hand, when a videographer records a video
image of himself, the monitor has to be turned to the same
direction of the camera lens. Therefore, it is necessary to rotate
the monitor with respect to a main body of the camera. Thus, a
complicated axis of rotation as provided in the conventional tablet
PC is required, which causes the decrease of reliability. In the
video camera using the invention, images can be displayed on both
the first display surface and the second display surface.
Accordingly, a simple hinge can be used as a substitute for a
complicated axis of rotation, thus reliability can be improved.
[0095] The video camera shown in FIGS. 11A and 11B comprises a main
body 1101, a lens 1102, a microphone 1103, a finder 1104, a dual
emission display 1105, and a hinge 1106. The dual emission display
1105 includes a first display surface 1107 and a second display
surface 1108. FIG. 11A shows the case in which the dual emission
display 1105 is used in closed position and an image is displayed
on the first display surface 1107. FIG. 11B shows the case in which
the dual emission display 1105 is used in open position and an
image can be displayed on both the first display surface 1107 and
the second display surface 1108. In this manner, a monitor can be
used in either direction without a complicated axis of rotation,
leading to the improvement in the mechanical reliability.
Embodiment 7
[0096] FIGS. 12A to 12D show a digital camera using the invention.
A digital camera in this embodiment comprises a main body 1201, a
shutter 1202, a finder 1203, a lens 1204, a monitor display portion
1205, and a hinge 1206. The monitor display portion 1205 includes a
first display surface 1207 and a second display surface 120B. A
conventional digital camera has a built-in monitor display portion
which is fixed in it. In the invention, the monitor display portion
can be used in either open position or closed position by using the
dual emission display device and the hinge 1206. FIG. 12A is a
front elevational view of the digital camera, FIG. 12B is a rear
elevational view of the same, FIG. 12C is a front elevational view
of the monitor in open position, and FIG. 12D is a rear elevational
view of the monitor in open position. In this manner, an image can
be monitored from either side with the monitor in open
position.
Embodiment 8
[0097] With reference to FIGS. 10A and 10B, an embodiment of the
invention will be explained. In this embodiment, a structure of a
dual emission display panel including first and second display
screens is described in detail. FIG. 10A shows an active element
using transistors, and FIG. 10B shows a passive matrix element.
[0098] In FIG. 10A, a driving transistor 1001, a first electrode
(pixel electrode) 1002, a light emitting layer 1003, and a second
electrode (counter electrode) 1004 are provided over a light
transmissive, substrate 1000. An overlapping area of the first
electrode 1002, the light emitting layer 1003 and the second
electrode 1004 corresponds to a light emitting element 1025. In the
invention, the first electrode 1002 and the second electrode 1004
are formed of a light transmissive material. Therefore, the light
emitting element 1025 emits light in the direction of the substrate
1000 (first direction) and in the opposite direction thereof
(second direction), and has a first display region 1005 and a
second display region 1006. It is to be noted that for a light
transmissive material of the first electrode 1002 and the second
electrode 1004, used is a light transmissive conductive film such
as ITO or aluminum having a thickness enough to transmit light.
[0099] In FIG. 10B, a first electrode (pixel electrode) 1060, a
light emitting layer 1061 and a second electrode (counter
electrode) 1062 are formed over the light transmissive substrate
1000. An overlapping area of the first electrode 1060, the light
emitting layer 1061 and the second electrode 1062 corresponds to
the light emitting element 1025. An insulating layer 1063 and a
resin layer 1064 are also provided to serve as banks.
[0100] As described above, the passive element has a structure in
which the light emitting layer 1061 is sandwiched between the
electrodes. For the light emitting layer 1061, a material composed
mainly of inorganic substances may be used. In this case, an
insulating layer may be provided between the first electrode 1060
and the light emitting layer 1061 or between the second electrode
1062 and the light emitting layer 1061. For this insulating layer,
aluminum oxide (Al.sub.2O.sub.3) and titanium oxide (TiO.sub.2) may
be alternately laminated by thermal CVD using absorption reaction
on a deposited surface.
[0101] This embodiment can be implemented in combination with other
embodiments.
Embodiment 9
[0102] With reference to FIGS. 8A and 8B, an embodiment of the
invention will be explained. In this embodiment, a structure of a
dual emission display panel which includes first and second display
screens and image sensor is described in detail.
[0103] In FIG. 8A, a driving transistor 801 and an emitting device
825 having a first electrode (pixel electrode) 802 formed of a
light transmissive material, a light emitting layer 803, and a
second electrode (counter electrode) 804 formed of a light
transmissive material are formed over a light transmissive
substrate 800. A light emitting element 825 emits light in the
direction of the substrate 800 (first direction) and in the
opposite direction thereof (second direction). An insulating layer
835 is formed on the second electrode 804. Over the insulating
layer 835 formed over the second electrode 804, provided are a
photoelectric converter 838 formed by laminating a P-type layer
831, an I-type (intrinsic) layer 832 and an N-type layer 833, an
electrode 830 connected to the P-type layer 83.1, and an electrode
834 connected to the N-type, layer 833.
[0104] In the above mentioned dual emission display panel, the
light emitting element 825 is used as a light source, and the
photoelectric converter 838 is used as an image sensor. The light
emitting element 825 and the photoelectric converter 838 are formed
over the same substrate 800. A light emitted from the light
emitting element 825 is reflected by an object 837 and directed to
the photoelectric converter 838. Then, a potential difference
between the two electrodes 830 and 834 of the photoelectric
converter 838 is changed and a current corresponding to the changed
potential difference is supplied between the two electrodes 830 and
834. Thus, data of the object 837 can be obtained by detecting the
amount of the supplied current, and the obtained data can be
displayed by using the light emitting element 825. It is to be
noted that when using an image sensor function, the object 837 is
desirably used closely contact with the display surface so that a
light emitted from the light emitting element 825 as a light source
is reflected by the object 837.
[0105] In other words, the light emitting element 825 is used for
both displaying an image and for the light source in reading data
of the object 837. Further, the dual emission display panel has two
functions: an image sensor function for reading data of the object
837 and a display function for displaying an image. In spite of
having these two functions, it is not necessary to provide a light
source and a light diffusing screen separately in the display
panel, which are usually required for using an image sensor
function. Therefore, the dual emission display panel of this
embodiment allows the display device to be reduced significantly in
size, thickness, and weight.
[0106] With reference to FIG. 8B, explanation is made on an example
of an equivalent circuit used for the above-described dual emission
display panel. One pixel 850 is shown in FIG. 8B. The pixel 850
comprises a subpixel 817 including the light emitting element 825
and a subpixel 849 including a photoelectric converter 838. The
subpixel 817 comprises a signal line 820, a power supply line 821,
a scan line 822, a switching transistor 823 for controlling a video
signal input, and a driving transistor 824 for supplying to the
light emitting element 825 a current corresponding to the input
video signal. It is to be noted that the configuration of the
subpixel 817 can also be applied to a typical circuit configuration
in a cross section of the transistor and the light emitting element
shown in FIG. 8A.
[0107] On the other hand, the subpixel 849 comprises a signal line
840, scan lines 842 and 843, a reset transistor 846 for resetting a
potential difference between two electrodes of the photoelectric
converter 83.8, an amplifier transistor 845 in which a current
corresponding to the potential difference between the two
electrodes of the photoelectric converter 838 is supplied between
the source and drain thereof, and a switching transistor 844 for
controlling an input of a signal which is read from the
photoelectric converter 838 to driving circuits.
[0108] It is to be noted that the active light emitting element and
the photoelectric converter are formed over the same substrate in
this embodiment, though the passive light emitting element and the
photoelectric converter as shown in FIG. 10B may be formed over the
same substrate. Further, although each pixel comprises the light
emitting element 825 and the photoelectric converter 838 in this
embodiment, the photoelectric converter 838 is not necessarily
provided in each pixel, and may be provided every several pixels in
accordance with an object to be read or usage of the portable
terminal. Accordingly, the open area ratio of the light emitting
element 825 is increased, thus bright images can be achieved.
[0109] This embodiment can be implemented in combination with other
embodiments.
Embodiment 10
[0110] FIG. 14 is a block diagram of a tablet PC using the
invention. The tablet PC in this embodiment corresponds to the one
described in Embodiment Mode. The tablet PC in this embodiment
comprises a CPU 1401, a HDD 1414, a keyboard 1415, an external
interface 1408, a nonvolatile memory 1407, volatile memory 1406, a
communication circuit 1405, a microphone 1412, a speaker 1413, an
audio controller 1409, a touch panel 1410, a touch panel controller
1411, a display controller 1404, a dual emission display 1403, and
a display select circuit 1402. The dual emission display 1403 in
this embodiment has to be changed the scan direction and images to
be displayed depending on a used display surface.
[0111] In view of the foregoing, the invention provides a structure
for selecting a display surface by detecting the angle of a hinge
1416 which connects a first housing with a second housing. When the
hinge 1416 is in open position (when using the keyboard 1415),
images corresponding to a main display are output. That is, the
display select circuit 1402 detects the angle data of the hinge
1416 and sends the data to the CPU 1401. Then, the CPU 1401
instructs the display controller 1404 to send data for the main
display to the dual emission display 1403.
[0112] When the hinge 1416 is in closed position (when using a
touch pen), images corresponding to a sub-display are output. That
is, the display select circuit 1402 detects the angle data of the
hinge 1416 and sends the data to the CPU 1401. Then, the CPU 1401
instructs the display controller 1404 to send data for the
sub-display to the dual emission display 1403. In such a manner,
the display surface can be changed.
Embodiment 11
[0113] In this embodiment, another embodiment of a dual emission
display panel used for the portable terminal of the invention is
explained with reference to FIGS. 17A to 17C. In FIGS. 17A and 17B,
reference numerals 1701 and 1702 denote polarizers, and 1703
denotes a dual emission display panel. FIG. 17A is a front
elevational view and FIG. 178 is a side elevational view. In this
embodiment, the dual emission display panel 1703 is interposed
between the polarizers 1701 and 1702. The two, polarizers are
arranged so that their polarization directions cross each other,
thus outside light can be cut off. The crossing angle between the
two polarization directions is in the range of 40 to 90 degrees,
preferably from 70 to 90 degrees, and if possible, at 90 degrees.
Light from the dual emission display panel 1703 transmits through
either of the two polarizers to display an image. Accordingly, a
black display is performed in the region in which no light is
emitted and no image is displayed. Thus, the far side of the dual
emission display panel is not transmitted in viewing from either
side.
[0114] Either or both of the polarizers 1701 and 1702 may be
rotatable, and the transmittance of the dual emission display panel
can be changed by changing the crossing angle. That is, a
brightness control function may be additionally provided.
[0115] An antireflective coating or an antireflective film may be
provided outside the polarizers 1701 and 1702 in order to reduce
the reflectance, and thereby improve the visual quality. Otherwise,
a half-wave plate or a quarter-wave plate (or the relevant films)
may be added. In this manner, an added film having an optical
function allows to enhance the visual quality and in particular, to
perform a black display more clearly.
[0116] This embodiment can be implemented in combination with other
embodiments.
Embodiment 12
[0117] FIG. 22 shows a portable telephone set using the display
device of the invention, which is charging. In FIG. 22, a portable
telephone set 2201 is charged in open position by using a battery
charger 2202, and display portions emit light on both sides of the
portable telephone set 2201. The portable telephone set 2201 may
also be charged in closed position. Generally in a display device
using a light emitting element, a light emitting element
deteriorates over time, and the brightness is decreased. In the
case of a display device having a light emitting element in each
pixel, in particular, lighting frequency of pixel is different by
location, thus degree of deterioration varies by location.
Therefore, a higher lightning frequency causes a pixel to
deteriorate quickly and image persistence which decreases the image
quality. In order to alleviate image persistence, an image is
displayed during charging and the like, in which the portable
telephone set is not used normally, and a pixel less frequently
used is lighted. As for an image displayed during charging, used
are an image displayed by lighting all the pixels, an image
obtained by inverting contrast of normal screen (idle screen, for
example), an image displayed by detecting pixels less frequently
used, and the like.
[0118] FIG. 20 is a block diagram corresponding to FIG. 22. In this
embodiment, the portable telephone set 2201 comprises a CPU 2001, a
HDD 2014, a keyboard 2015, an external interface 2008, a
nonvolatile memory 2007, a volatile memory 2006, a communication
circuit 2005, a microphone 2012, a speaker 2013, an audio
controller 2009, a touch panel 2010, a touch panel controller 2011,
a display controller 2004, a dual emission display 2003, and a
display select circuit 2002. A battery charger 2017 detects a
signal showing a charge status and sends the signal to the CPU
2001. Then, the CPU 2001 instructs the display controller 2004 to
display the corresponding signal, thus the dual emission display
2003 emits light.
[0119] FIG. 21 shows an example of a controller for producing the
above-described image whose contrast is inverted from that of
normal display screen. An output signal from an image signal select
switch 2106 is input to a switch 2107. A display controller 2102
determines whether the output signal from the image signal select
switch 2106 is input directly to a display 2101 or input after
being inverted. When contrast has to be inverted, the signal may be
input after being inverted. A switch 2103, a memory A 2104 and a
memory B 2105 in FIG. 21 function as a switch 903, a memory A 904
and a memory B 905 in FIG. 9, respectively. In the case of
displaying an image using all the pixels lighted, a constant
voltage may be input to the display 2101 (not shown).
[0120] In such a manner, deterioration of visual quality can be
prevented by emitting light during charging so as to alleviate
image persistence. This embodiment can be implemented in
combination with other embodiments.
Embodiment 13
[0121] Another example of pixel applied to the invention will be
explained with reference to FIGS. 23 and 24. A pixel shown in a
circuit diagram of FIG. 23 comprises a light emitting element 2304,
a switching transistor 2301 for controlling a video signal input to
the pixel, and transistors 2302 and 2303 for controlling current
supply to the light emitting element 2304. In this embodiment, the
transistor 2302 corresponds to a driving transistor, and the
transistor 2303 corresponds to a current control transistor. A
capacitor 2305 for storing a video signal potential may be
additionally provided in the pixel as in Embodiment Mode of the
invention.
[0122] The driving transistor 2302 and the current control
transistor 2303 have the same conductivity. Both of them have
P-type conductivity in this embodiment, though they may have N-type
conductivity. A threshold voltage of the driving transistor 2302 is
set higher than that of the current control transistor 2303, and
more preferably, the driving transistor 2302 is to be a normally-ON
transistor. Further, in the invention, the ratio of the channel
length to the channel width (L/W) of the driving transistor 2302 is
larger than that of the current control transistor 2303, thereby
the driving transistor 2302 is operated in saturation region and
the current control transistor 2302 is operated in linear region.
Specifically, in the driving transistor 2302, the channel length
(L) is set longer, preferably five times longer or more, than the
channel width (W). Meanwhile, in the current control transistor
2303, the channel length (L) is set equal to or shorter than the
channel width (W).
[0123] The gate of the switching transistor 2301 is connected to a
scan line Gj (j=1 to y). One of the source and drain of the
switching transistor 2301 is connected to a signal line Si (i=1 to
x) and the other is connected to the gate of the driving transistor
2302 and the gate of the current control transistor 2303. The
driving transistor 2302 and the current control transistor 2303 are
connected in series. The driving transistor 2302 and the current
control transistor 2303 are connected to a power supply line Vi
(i=1 to x) and the light emitting element 2304 so that a current
from the power supply line Vi is supplied to the light emitting
element 2304 as a drain current of the driving transistor 2302 and
of the current control transistor 2303. In this embodiment, the
source of the current control transistor 2303 is connected to the
power supply line Vi (i=1 to x), and the drain of the driving
transistor 2302 is connected to a pixel electrode of the light
emitting element 2304.
[0124] The light emitting element 2304 comprises an anode, a
cathode and an electro luminescent layer interposed between the
anode and the cathode. When the anode is connected to either the
driving transistor 2302 or the current control transistor 2303, the
anode is used as a pixel electrode and the cathode is a counter
electrode. Meanwhile, when the cathode is connected to either the
driving transistor 2302 or the current control transistor 2303, the
cathode is used as a pixel electrode and the anode is a counter
electrode. A voltage is supplied from a power supply to each of the
counter electrode of the light emitting element 2304 and the power
supply line Vi so as to supply a forward bias current to the light
emitting element 2304.
[0125] One of the two electrodes of the capacitor 2305 is connected
to the power supply line Vi and the other is connected to the gates
of the driving transistor 2302 and the current control transistor
2303. The capacitor 2305 is provided to store the gate voltage of
the driving transistor 2302 and of the current control transistor
2303, when the switching transistor 2301 is turned OFF. Although
the capacitor 2305 is provided in FIG. 23, the invention is not
exclusively limited to this configuration, and the capacitor is not
necessarily provided.
[0126] In the case where the source or the drain of the driving
transistor 2302 is connected to the anode of the light emitting
element 2304, it is desirable that the driving transistor 2302 has
P-type conductivity. On the other hand, in the case where the
source or the drain of the driving transistor 2302 is connected to
the cathode of the light emitting element 2304, it is desirable
that the driving transistor 2302 has N-type conductivity.
[0127] With reference to FIG. 24, explanation will be made on a
structure of a dual emission display panel which includes first and
second display surfaces and uses the pixel circuit shown in FIG.
23. In FIG. 24, a driving transistor 2401, a current control
transistor 2407, a first electrode (pixel electrode) 2402, a light
emitting layer 2403, and a second electrode (counter electrode)
2404 are provided over a light transmissive substrate 2400. The
driving transistor 2401 is formed so as to be a normally-ON
transistor. For example, elements such as boron, which imparts one
conductivity, is added in a channel forming region by ion
implantation or ion doping.
[0128] A light emitting element 2425 is formed by laminating the
first electrode 2402, the light emitting layer 2403 and the second
electrode 2404. In this embodiment, the first electrode 2402 and
the second electrode 2404 are formed of a light transmissive
material. Accordingly, the light emitting element 2425 emits light
in the direction of the substrate 240 (first direction) and the
opposite direction thereof (second direction), and comprises a
first display region 2405 and a second display region 2406. It is
to be noted that for a light transmissive material for the first
electrode 2402 and the second electrode 2404, used are aluminum
having a thickness enough to transmit light, or a light
transmissive conductive film such as indium tin oxide, zinc oxide,
or indium tin oxide added with silicon oxide, gallium, zinc oxide,
tungsten oxide and the like.
[0129] This embodiment can be implemented in combination with other
embodiments.
* * * * *