U.S. patent application number 11/548024 was filed with the patent office on 2007-04-26 for semiconductor device.
This patent application is currently assigned to SEMICONDUCTOR ENERGY LABORATORY CO., LTD.. Invention is credited to Seiko AMANO, Ryota FUKUMOTO, Hiroyuki MIYAKE, Mitsuaki OSAME, Yoshifumi TANADA.
Application Number | 20070090385 11/548024 |
Document ID | / |
Family ID | 37671966 |
Filed Date | 2007-04-26 |
United States Patent
Application |
20070090385 |
Kind Code |
A1 |
FUKUMOTO; Ryota ; et
al. |
April 26, 2007 |
SEMICONDUCTOR DEVICE
Abstract
The present invention provides a semiconductor device in which a
power line is not affected by noise due to a voltage drop caused by
instantaneous high-current consumption in the buffer portion and
that has no possibility that a logic portion malfunctions. In a
case where the same potential is supplied to a logic portion and a
buffer portion, by a method in which separate FPC terminals are
used for the logic portion and the buffer portion, or by a method
in which the FPC terminal is shared but a power line is branched
for the logic portion and the buffer portion at a point close to
the FPC terminal, a problem that the logic portion is affected by
noise generated by a voltage drop of the power line due to
instantaneous high-current consumption in the buffer portion can be
prevented.
Inventors: |
FUKUMOTO; Ryota;
(Atsugi-shi, Kanagawa-ken, JP) ; OSAME; Mitsuaki;
(Atsugi-shi, Kanagawa-ken, JP) ; MIYAKE; Hiroyuki;
(Atsugi-shi, Kanagawa-ken, JP) ; TANADA; Yoshifumi;
(Atsugi-shi, Kanagawa-ken, JP) ; AMANO; Seiko;
(Atsugi-shi, Kanagawa-ken, JP) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
SEMICONDUCTOR ENERGY LABORATORY
CO., LTD.
398, Hase
Atsugi-shi
JP
|
Family ID: |
37671966 |
Appl. No.: |
11/548024 |
Filed: |
October 10, 2006 |
Current U.S.
Class: |
257/99 ;
257/E27.111 |
Current CPC
Class: |
G02F 1/1345 20130101;
G09G 3/3225 20130101; H01L 27/12 20130101; G09G 2300/0426 20130101;
G09G 2310/0275 20130101; G09G 2330/02 20130101; G09G 3/20
20130101 |
Class at
Publication: |
257/099 |
International
Class: |
H01L 33/00 20060101
H01L033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 21, 2005 |
JP |
2005-307856 |
Claims
1. A semiconductor device comprising: a driver circuit including a
buffer portion and a logic portion, which is formed over a
substrate; a first connecting terminal over the substrate for
supplying a voltage from an external circuit; a second connecting
terminal over the substrate for supplying the voltage from the
external circuit; a first power line connecting the first
connecting terminal with the buffer portion electrically; and a
second power line connecting the second connecting terminal with
the logic portion electrically.
2. The semiconductor device according to claim 1, wherein a width
of the first power line is wider than a width of the second power
line.
3. The semiconductor device according to claim 1, wherein the
voltage has a ground potential.
4. The semiconductor device according to claim 1, wherein the
substrate has an insulating surface.
5. The semiconductor device according to claim 1, further
comprising a pixel portion connected to the buffer portion, the
pixel portion is formed over the substrate.
6. The semiconductor device according to claim 1, wherein the
driver circuit performs a line-sequential driving.
7. The semiconductor device according to claim 1, wherein the logic
portion comprises at least one of a latch circuit and a shift
register circuit.
8. The semiconductor device according to claim 1, wherein the
buffer portion comprises at least one of a level shifter circuit
and a buffer circuit.
9. The semiconductor device according to claim 1, wherein the
semiconductor device is a display device including a self-luminous
element, or a display device including a liquid crystal
element.
10. A semiconductor device comprising: a driver circuit including a
buffer portion and a logic portion, which is formed over a
substrate; a connecting terminal over the substrate for supplying a
voltage from an external circuit; and a power line extended from
the connecting terminal, wherein the power line is branched at a
point of 3/5or less of a length of the power line from the
connecting terminal to the buffer portion, a first branch of the
power line is electrically connected to the buffer portion and a
second branch of the power line is electrically connected to the
logic portion.
11. The semiconductor device according to claim 10, wherein a width
of the first branch of the power line is wider than a width of the
second branch of the power line.
12. The semiconductor device according to claim 10, wherein the
voltage has a ground potential.
13. The semiconductor device according to claim 10, wherein the
substrate has an insulating surface.
14. The semiconductor device according to claim 10, further
comprising a pixel portion connected to the buffer portion, the
pixel portion is formed over the substrate.
15. The semiconductor device according to claim 10, wherein the
driver circuit performs a line-sequential driving.
16. The semiconductor device according to claim 10, wherein the
logic portion comprises at least one of a latch circuit and a shift
register circuit.
17. The semiconductor device according to claim 10, wherein the
buffer portion comprises at least one of a level shifter circuit
and a buffer circuit.
18. The semiconductor device according to claim 10, wherein the
semiconductor device is a display device including a self-luminous
element, or a display device including a liquid crystal
element.
19. The semiconductor device according to claim 10, wherein the
power line is branched at a point of 1/3or less of the length of
the power line from the connecting terminal to the buffer
portion.
20. A semiconductor device comprising: a driver circuit including a
first circuit and a second circuit, which is formed over a
substrate; a first connecting terminal over the substrate for
supplying a voltage from an external circuit; a second connecting
terminal over the substrate for supplying the voltage from the
external circuit; a first power line connecting the first
connecting terminal with the first circuit electrically; and a
second power line connecting the second connecting terminal with
the second circuit electrically, wherein the first circuit and the
second circuit is connected electrically.
21. The semiconductor device according to claim 20, wherein a width
of the first power line is wider than a width of the second power
line.
22. The semiconductor device according to claim 20, wherein the
voltage has a ground potential.
23. The semiconductor device according to claim 20, wherein the
substrate has an insulating surface.
24. The semiconductor device according to claim 20, further
comprising a pixel portion connected to the first circuit, the
pixel portion is formed over the substrate.
25. The semiconductor device according to claim 20, wherein the
driver circuit performs a line-sequential driving.
26. The semiconductor device according to claim 20, wherein the
second circuit comprises at least one of a latch circuit and a
shift register circuit.
27. The semiconductor device according to claim 20, wherein the
first circuit comprises at least one of a level shifter circuit and
a buffer circuit.
28. The semiconductor device according to claim 20, wherein the
semiconductor device is a display device including a self-luminous
element, or a display device including a liquid crystal
element.
29. A semiconductor device comprising: a driver circuit including a
first circuit and a second circuit, which is formed over a
substrate; a connecting terminal over the substrate for supplying a
voltage from an external circuit; and a power line extended from
the connecting terminal, wherein the power line is branched at a
point of 3/5or less of a length of the power line from the
connecting terminal to the first circuit, a first branch of the
power line is electrically connected to the first circuit and a
second branch of the power line is electrically connected to the
second circuit, and wherein the first circuit and the second
circuit is connected electrically.
30. The semiconductor device according to claim 29, wherein a width
of the first branch of the power line is wider than a width of the
second branch of the power line.
31. The semiconductor device according to claim 29, wherein the
voltage has a ground potential.
32. The semiconductor device according to claim 29, wherein the
substrate has an insulating surface.
33. The semiconductor device according to claim 29, further
comprising a pixel portion connected to the first circuit, the
pixel portion is formed over the substrate.
34. The semiconductor device according to claim 29, wherein the
driver circuit performs a line-sequential driving.
35. The semiconductor device according to claim 29, wherein the
second circuit comprises at least one of a latch circuit and a
shift register circuit.
36. The semiconductor device according to claim 29, wherein the
first circuit comprises at least one of a level shifter circuit and
a buffer circuit.
37. The semiconductor device according to claim 29, wherein the
semiconductor device is a display device including a self-luminous
element, or a display device including a liquid crystal
element.
38. The semiconductor device according to claim 29, wherein the
power line is branched at a point of 1/3or less of the length of
the power line from the connecting terminal to the first circuit.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for leading a
power line in a field of a semiconductor device using a
semiconductor element.
[0003] 2. Description of the Related Art
[0004] A driver circuit such as a source driver or a gate driver
constituting a display device includes a logic circuit (hereinafter
referred to as a logic portion) which sequentially outputs pulses
according to desired timing and performs arithmetic processing such
as capture of data, such as a shift resister circuit or a latch
circuit, and a circuit (hereinafter referred to as a logic portion)
which amplifies signal amplitude such as a buffer circuit or a
level shifter circuit.
[0005] Such a driver circuit has been developed as a control
portion in a display device having a liquid crystal element
(hereinafter referred to as a liquid crystal display device) or a
display device having a self-luminous element (hereinafter referred
to as a light emitting device).
[0006] Conventionally, a power line supplying the same potential to
a logic portion and a buffer portion is shared by the logic portion
and the buffer portion, and the potential is applied to a necessary
part in the logic portion and the buffer portion by the same
wiring. In particular, a power line for supplying a ground
potential is usually shared by a logic portion and a buffer
portion. By sharing a wiring in this way, an area occupied by the
wiring can be decreased, and a frame of a display device is
narrowed.
[0007] As shown in FIG. 6, conventionally, a power line 601
supplying the same potential to a logic portion 105 and a buffer
portion 108 is led from one FPC (flexible printed circuit) terminal
600 for power, so that the logic portion 105 and the buffer portion
108 share the power line 601 led from the FPC terminal 600 for
power up to near the logic portion and the buffer portion. This is
because leading of the power line is easy and a space for layout
can be small when the power line is shared up to near the circuit
portions.
[0008] However, when the FPC terminal 600 for power and the power
line 601 led from the FPC terminal 600 for power are shared by the
logic portion 105 and the buffer portion 108, there is a
possibility that an instantaneous high-current consumed by the
buffer portion 108 at the time of writing into a pixel causes a
voltage drop of the power line 601, and noise is generated, which
leads to malfunction of the logic portion 105 affected by the
noise.
[0009] This results from the fact that the logic portion which is a
circuit for outputting a pulse consumes less current compared to
the buffer portion, and the buffer portion which amplifies signal
amplitude consumes more current compared to the logic portion.
[0010] In a case of a source driver, the above-described problem is
more serious, since a source driver operates faster than a gate
driver and has a higher load than a gate driver. In a source
driver, an instantaneous high-current is consumed at the time of
data writing, and the larger a current value is, the larger a
voltage drop of a power line becomes. Therefore, when a logic
portion and a buffer portion of the source driver share the power
line, there is a high possibility that the logic portion is
affected by noise generated due to a voltage drop of the power line
of the buffer portion, and that the logic portion malfunctions.
[0011] In addition, particularly in a case of line-sequential
driving, the above-described problem is serious, since a source
driver writes data for one line at a time in a case of the
line-sequential driving. Therefore, when a logic portion and a
buffer portion of a source driver performing line-sequential
driving share the power line, there is a high possibility that the
logic portion is largely affected by noise generated due to a
voltage drop of the power line of the buffer portion, and that the
logic portion malfunctions.
[0012] As is clear from Ohm's law, a voltage drop is expressed by
V=IR. V [V] represents a voltage (a value of a voltage drop); I
[A], a current; and R [.OMEGA.], resistance. In this case, R
[.OMEGA.] is wiring resistance and the value thereof is the same in
the logic portion and the buffer portion, but I [A] is different
between the logic portion and the buffer portion. For example, a
low potential side of a power line which is led from an FPC
terminal for power and connected to each of the logic portion and
the buffer portion is set to be the same, and different potentials
are applied to the logic portion and the buffer portion for a high
potential side. Generally, high output amplitude is necessary in a
buffer portion, so that a potential to be applied to the buffer
portion is set to be higher than the logic portion, and output load
capacitance of the buffer portion is higher than the logic
portion.
[0013] Therefore, a large voltage drop can occur in the power line
in the buffer portion where an instantaneous high-current is
consumed. At this time, in a case where the logic portion and the
buffer portion share the power line supplying the same potential,
there is a possibility that the logic portion is affected by noise
generated due to a large voltage drop of the power line of the
buffer portion, and accurate data is not captured when capturing
data; thus causing a problem such as a display defect.
SUMMARY OF THE INVENTION
[0014] In view of the foregoing, it is an object of the present
invention to solve a problem that a logic portion is affected by
noise generated due to a large voltage drop of a power line of a
buffer portion, and that the logic portion malfunctions.
[0015] In view of the above-described problem, one feature of the
present invention is that separate power lines are used for a logic
potion and a buffer portion although it is possible to share one
power line between the logic portion and the buffer portion, so
that malfunction of the logic circuit affected by noise does not
occur. By using separate power lines for the logic portion and the
buffer portion instead of sharing one power line, the logic portion
can be prevented from being affected by noise caused by high power
consumption in the buffer circuit.
[0016] For example, in the present invention, a wiring for
supplying a ground potential which is the same potential for a
logic portion and a buffer portion is not shared by the logic
portion and the buffer portion, and separate connecting terminals
for an external signal (hereinafter referred to as FPC terminals)
are used for the logic portion and the buffer portion. By using
separate FPC terminals for the logic portion and the buffer
portion, instead of using one power line shared by the logic
portion and the buffer portion, the logic portion can be prevented
from being affected by noise caused by high power consumption in
the buffer circuit.
[0017] Alternatively, in the present invention, a power line
supplying a ground potential which is the same potential for a
logic portion and a buffer portion is branched at a point far from
a circuit to be supplied with the ground potential, specifically,
at a point far from the logic portion and the buffer portion, that
is, at a point close to an FPC terminal. By branching a power line
at a point close to the FPC terminal, the logic portion can be
prevented from being affected by noise caused by high power
consumption in the buffer circuit.
[0018] One mode of the present invention is a semiconductor device
including: an external circuit; a driver circuit including a buffer
portion and a logic portion, which is formed over a substrate
having an insulating surface; and over the substrate, a first
connecting terminal and a second connecting terminal, for inputting
a signal from the external circuit, which are provided on one side
of the substrate. In the semiconductor device, a first power line
extended from the first connecting terminal is electrically
connected to the buffer portion; a second power line extended from
the second connecting terminal is electrically connected to the
logic portion; and the first connecting terminal and the second
connecting terminal have the same potential.
[0019] Another mode of the present invention is a semiconductor
device including: an external circuit; a driver circuit including a
buffer portion and a logic portion, which is formed over a
substrate having an insulating surface; and over the substrate, a
first connecting terminal and a second connecting terminal, for
inputting a signal from the external circuit, which are provided on
one side of the substrate. In the semiconductor device, a first
power line extended from the first connecting terminal is
electrically connected to the buffer portion; a second power line
extended from the second connecting terminal is electrically
connected to the logic portion; the first connecting terminal and
the second connecting terminal have the same potential; and a width
of the first power line is wider than a width of the second power
line.
[0020] Another mode of the present invention is a semiconductor
device including: an external circuit; a driver circuit including a
buffer portion and a logic portion, which is formed over a
substrate having an insulating surface; and over the substrate, a
connecting terminal for inputting a signal from the external
circuit, which is provided on one side of the substrate. In the
semiconductor device, a power line extended from the connecting
terminal to the logic portion is branched at a point of 3/5or less
of a length of the power line from the connecting terminal so that
one of the branched power lines is electrically connected to the
buffer portion and the other is electrically connected to the logic
portion.
[0021] Another mode of the present invention is a semiconductor
device including: an external circuit; a driver circuit including a
buffer portion and a logic portion, which is formed over a
substrate having an insulating surface; and over the substrate, a
connecting terminal for inputting a signal from the external
circuit, which is provided on one side of the substrate. In the
semiconductor device, a power line extended from the connecting
terminal to the logic portion is branched at a point of 3/5or less
of a length of the power line from the connecting terminal so that
one of the branched power lines is electrically connected to the
buffer portion and the other is electrically connected to the logic
portion; and a width of the one of the branched power lines is
wider than a width of the other power line.
[0022] In the present invention, "the same potential" can be a
ground potential.
[0023] In the present invention, the driver circuit is provided in
a source driver.
[0024] In the present invention, the logic portion includes a latch
circuit and a shift resister circuit.
[0025] In the present invention, the driver circuit includes a
latch circuit for performing line-sequential driving.
[0026] In the present invention, the buffer portion includes a
level shifter circuit and a buffer circuit.
[0027] A semiconductor device of the present invention is a display
device including a self-luminous element, or a display device
including a liquid crystal element.
[0028] According to the present invention, a problem that a logic
portion is affected by noise generated by a voltage drop of a power
line due to high-current consumption in a buffer portion and that
the logic portion malfunctions can be solved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a view showing a driver portion provided with a
plurality of power lines each connected to an FPC terminal.
[0030] FIG. 2 is a view showing a driver portion provided with a
plurality of power lines connected to one FPC terminal.
[0031] FIGS. 3A and 3B are block diagrams each showing a light
emitting device of the present invention.
[0032] FIG. 4 is a view showing an FPC terminal portion of the
present invention.
[0033] FIG. 5 is a view showing a source driver portion of the
present invention.
[0034] FIG. 6 is a view showing a driver portion provided with a
conventional power line.
[0035] FIGS. 7A and 7B are views each showing a light emitting
device of the present invention.
[0036] FIGS. 8A to 8F are views each showing an example in which
the present invention is applied to an electronic device.
[0037] FIG. 9 is a diagram showing a pixel circuit of the present
invention.
[0038] FIGS. 10A and 10B are diagrams each showing a pixel circuit
of the present invention.
[0039] FIGS. 11A and 11B are views each showing a light emitting
device of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0040] Embodiment modes of the present invention will be described
hereinafter with reference to the drawings. However, the present
invention can be carried out in various modes, and it is easily
understood by those skilled in the art that the modes and details
can be changed in various ways without departing from the spirit
and scope of the present invention. Therefore, the present
invention is not interpreted as being limited to the following
description of the embodiment modes. In all the drawings for
describing the embodiment modes, the same reference numerals and
symbols are used for denoting the same portions or portions having
the same functions, and repeated descriptions thereof will be
omitted.
(Embodiment Mode 1)
[0041] In the present embodiment mode, an example method for
leading a power line extended from an FPC terminal will be
described.
[0042] In FIG. 1, a semiconductor device including a source driver
provided with a portion performing line-sequential driving is
shown. FIG. 1 is a view showing a way of leading a power line in
the vicinity of an FPC terminal portion provided on one side of a
substrate and a source driver circuit, as a method for leading a
power line of the present invention. Hereinafter, a structure of
the FPC terminal portion and the inside of the source diver will be
described.
[0043] The semiconductor device includes an FPC terminal portion
100, a source driver 109, and a pixel portion 112, provided over an
insulating surface. The FPC terminal portion includes a plurality
of FPC terminals. The number of FPC terminals may be set according
to need. However, when the number of FPC terminals is large, there
is a possibility that poor connection occurs at the time of
connection with an external circuit, so that the number is
preferably small. The source driver 109 includes a shift resister
circuit 103, a latch circuit 104, a level shifter circuit 106, and
a buffer circuit 107. In the source driver, data for one line is
written at a time into the latch circuit 104, and line-sequential
driving is performed. A low current consumption portion in which a
pulse is sequentially outputted according to desired timing and
capture of data or the like is performed, such as the shift
resister circuit 103 and the latch circuit 104, is a logic portion
105, and a high current consumption portion in which signal
amplitude is amplified and an instantaneous high-current is
consumed, such as the buffer circuit 107 and the level shifter
circuit 106, is a buffer portion 108. In addition, an output of the
buffer circuit 107 is Sline, and expressed by Sline_01 to Sline_n
(n is a natural number). The Sline_01 to Sline_n are electrically
connected to a signal line included in the pixel portion 112, and a
predetermined video signal is inputted thereto.
[0044] The logic portion and the buffer portion are respectively
connected to separate power lines (that is, wirings) which are
respectively led from separated FPC terminals. As a result, a
problem that the logic portion is affected by noise generated by a
voltage drop of the power line caused by high-current consumption
in the buffer portion and that the logic portion malfunctions, can
be solved.
[0045] Specifically, the FPC terminal portion 100 includes a first
FPC terminal 101 and a second FPC terminal 102, and the
semiconductor device further includes a first power line 110
extended from the first FPC terminal 101 and a second power line
111 extended from the second FPC terminal 102. Potential of the
first power line 110 and the second power line 111 are set to be
the same potential, which potential may be potential of a high
potential side or a low potential side. For example, the potential
of the first power line 110 and the second power line 111 can be
4.5 to 5.5 V in a case of a high potential side, and can be 0 V in
a case of a low potential side. It is to be noted that the
potential differs depending on a power line used for the
semiconductor device. For example, the potential of the first power
line 110 and the second power line 111 can be a ground
potential.
[0046] In particular, a wiring supplying a fixed potential such as
a ground potential is conventionally shared by many circuits in
order to reduce a wiring region. However, a feature of the present
invention is that separate wirings or separate FPC terminals for
supplying a common potential are used. That is, as shown in FIG. 1,
as FPC terminals for power, supplying the same potential to the
logic portion and the buffer portion, the separate first FPC
terminal 101 and second FPC terminal 102 are used. And the first
power line 110 and the second power line 111 are led from the first
FPC terminal 101 and the second FPC terminal 102 toward the logic
portion 105 and the buffer portion 108, respectively. Since the
first FPC terminal 101 and the second FPC terminal 102 have the
same potential, the first power line 110 and the second power line
111 also have the same potential.
[0047] In such a display device of line-sequential driving, since
writing into pixels for one line in a pixel portion 112 is
performed at once in the buffer portion 108, transistors
(typically, thin film transistors: TFFs) included in the buffer
portion 108 are driven all at once. Then, an instantaneous
high-current is consumed in the buffer portion 108. Due to this
instantaneous high-current consumption, a potential of the first
power line 110 instantaneously becomes low in a case where it is a
power line of a high potential side, or a potential of the first
power line 110 instantaneously becomes high in a case where it is a
power line of a low potential side. Accordingly, a phenomenon of a
voltage drop occurs. In the present invention, however, the
separate first FPC terminal 101 and second FPC terminal 102 are
used, and the first power line 110 connected to the logic portion
105 and the second power line 111 connected to the buffer portion
108 are provided separately. Therefore, it becomes possible to
reduce the problem that the logic portion 105 is affected by noise
generated by a voltage drop of the first power line 110.
[0048] As described above, by using separate FPC terminals for
power, supplying the same potential to the logic portion and the
buffer portion, instead of sharing a power line and an FPC terminal
for power as in a conventional case, it becomes possible to reduce
the problem that the logic portion 105 is affected by noise and
malfunctions, even when a voltage of the first power line drops and
noise is generated, since the logic portion and the buffer portion
do not share the power line.
[0049] In the present embodiment mode, the explanation is made
setting a low current consumption portion in which a pulse is
sequentially outputted according to desired timing and capture of
data or the like is performed, such as the shift resister circuit
and the latch circuit, to be a logic portion, and setting a high
current consumption portion in which signal amplitude is amplified
and an instantaneous high-current is consumed, such as the buffer
circuit and the level shifter circuit, to be a buffer circuit.
However, the gist of the explanation of the present invention is
that separate power lines are used in a case of supplying power
lines having the same potential to a circuit with large current
consumption and a circuit with small current consumption.
Therefore, a scope where the present invention can be applied is
not limited to the logic portion and the buffer portion. For
example, the present invention can be applied to a shift resister
circuit and a latch circuit in a logic portion.
(Embodiment Mode 2)
[0050] In the present embodiment mode, a mode will be described, in
which an FPC terminal for power is shared by a logic portion and a
buffer portion, and a power line is branched at a point which is as
far from a circuit to be driven as possible, preferably at a point
close to the FPC terminal, so that a problem that noise is
generated due to a voltage drop of the power line and that a logic
portion malfunctions by being affected by the noise is reduced.
[0051] FIG. 2 shows an example of the present embodiment mode. In
the present embodiment mode, an explanation will be made taking a
source driver capable of line-sequential driving as an example, in
the same way as FIG. 1. FIG. 2 is a view showing a way of leading a
power line in the vicinity of an FPC terminal portion and a source
driver circuit, as a method for leading a power line of the present
invention. Hereinafter, a structure of the FPC terminal portion and
the inside of the source diver will be described.
[0052] In the same way as the above-described embodiment mode, a
semiconductor device includes an FPC terminal portion 100, a source
driver 109, and a pixel portion 112, provided over an insulating
surface. A difference from the above-described embodiment mode is
that a power line led from an FPC terminal 200 and branched into
two wirings, one of which is a first power line 201, and the other
of which is a second power line 202, at a point close to the FPC
terminal 200, is provided. The branching point may be provided at a
point of 3/5or less of a length of the power line from the FPC
terminal, and preferably, at a point of 1/3or less of a length of
the power line from the FPC terminal. For example, in a case where
a length of the power line from the FPC terminal to the buffer
portion is 12000 .mu.m, the branching point may be provided at a
point 2300 .mu.m from the FPC terminal. In this way, the longer a
distance between the buffer portion which generates noise and the
branching point of the power line is, the better the problem can be
prevented, in which the logic portion is affected by noise and
malfunctions. This is because the longer a distance from the buffer
portion is, the smaller the noise generated by a voltage drop on
the power line from the buffer portion to the FPC terminal is.
[0053] Potential of the first power line 201 and the second power
line 202 may be potential of a high potential side or a low
potential side. For example, the potential of the first power line
201 and the second power line 202 can be 4.5 to 5.5 V in a case of
a high potential side, and can be 0 V in a case of a low potential
side. It is to be noted that the potential differs depending on a
power line used for a semiconductor device. It is to be noted that
the first power line 201 and the second power line 202 share the
FPC terminal 200, so that the same potential is applied to each of
them. For example, the potential of the first power line 201 and
the second power line 202 can be a ground potential.
[0054] As shown in FIG. 2, the first power line 201 and the second
power line 202, which are connected to the FPC terminal 200 having
the same potential and branched at a point close to the FPC
terminal, are connected to the logic portion 105 and the buffer
portion 108, respectively. Since the first power line 201 and the
second power line 202 share the FPC portion 200, they have the same
potential. In addition, in a case where the FPC terminal for the
power line with the same potential is shared and the power line is
branched, it is preferable that the power line be branched at a
point far from a circuit to be driven, that is, at a point close to
the FPC terminal 200. This is because an effect of noise caused by
a voltage drop cannot be prevented if the power line with the same
potential is branched at a point close to circuits such as the
logic portion 105 and the buffer portion 108.
[0055] In such a display device, when the buffer portion 108
performs writing into a pixel and TFT's are driven all at once, the
buffer portion 108 consumes an instantaneous high-current. Due to
this instantaneous high-current consumption, a potential of the
first power line 201 instantaneously becomes low in a case where it
is a power line of a high potential side, or a potential of the
first power line 201 instantaneously becomes high in a case where
it is a power line of a low potential side. Accordingly, a
phenomenon of a voltage drop occurs. In the present invention,
however, the power line is branched at a point close to the FPC
terminal 200 into the first power line 201 connected to the logic
portion 105 and the second power line 202 connected to the buffer
portion 108. Therefore, it becomes possible to reduce the problem
that the logic portion 105 is affected by noise generated by a
voltage drop of the first power line 201.
[0056] As described above, by branching a power line at a point
close to an FPC terminal while the FPC terminal for power is
shared, although the power line with the same potential is
conventionally shared, it becomes possible to reduce the problem
that the logic portion is affected by noise and malfunctions, even
when a voltage of the first power line 201 drops and noise is
generated.
[0057] Since an FPC terminal for power for a power line with the
same potential can be shared in the present embodiment, effects of
the present invention can be obtained without increasing the number
of FPC terminals.
(Embodiment Mode 3)
[0058] In the present embodiment mode, an appearance of one mode of
a light emitting device of the present invention will be described
with reference to FIGS. 7A and 7B. FIG. 7A is a top view of a panel
which is formed by sealing a TFT and a light emitting element
formed over a first substrate between the first substrate and a
second substrate, using a sealant. FIG. 7B corresponds to a
cross-sectional view along a line A-A' in FIG. 7A.
[0059] Over a first substrate 4001, a pixel portion 4002, a source
driver 4003 including a logic portion 4023 and a buffer portion
4013, and a gate driver 4004 are provided, and a sealant 4005 is
also provided so as to surround the pixel portion. In addition, a
second substrate 4006 is provided over the pixel potion 4002 with
the sealant 4005 interposed therebetween. In the display device
shown in FIGS. 7A and 7B, the pixel portion 4002, the source driver
4003, and the gate driver 4004 are sealed with a filler 4007 by the
first substrate 4001, the sealant 4005, and the second substrate
4006.
[0060] The pixel portion 4002, the source driver 4003, and the gate
driver 4004 formed over the first substrate 4001 have a plurality
of TFTs, and a TFT 4008 included in the source driver 4003 and a
TFT 4009 included in the pixel portion 4002 are shown as examples
in FIG. 7B.
[0061] Reference numeral 4011 corresponds to the light emitting
element, and part of a wiring 4017 connected to a drain of the TFT
4009 functions as a first electrode of the light emitting element
4011. A transparent conductive film 4012 functions as a second
electrode of the light emitting element 4011. It is to be noted
that a structure of the light emitting element 4011 is not limited
to the structure shown in the present embodiment mode. As the
above-described embodiment modes, the structure of the light
emitting element 4011 can be arbitrarily changed according to a
direction of light emitted from the light emitting element 4011,
polarity of the TFT 4009, or the like. The direction of light
emitted from the light emitting element 4011 can be the first
substrate 4001 side, the second substrate 4006 side, or both the
first substrate 4001 side and the second substrate 4006 side.
[0062] Although not shown in the cross-sectional view of FIG. 7B,
various signals and voltage are supplied to the source driver 4003,
the gate driver 4004, or the pixel portion 4002, from an FPC
terminal 4016 via power lines 4014 and 4015.
[0063] In the present embodiment, the FPC terminal 4016 is formed
of the same conductive film as the first electrode of the light
emitting element 4011. Furthermore, the power line 4014 is formed
of the same conductive film as a wiring 4017. In addition, the
power line 4015 is formed of the same conductive film as a gate
included in each of the TFT 4009 and the TFT 4008.
[0064] The FPC terminal 4016 is electrically connected to a
terminal included in an FPC 4018 via an anisotropic conductive film
4019. As seen from the cross-sectional view in FIG. 7B, in a power
line separating portion 4020, a voltage is supplied from the FPC
terminal 4016 via the power lines 4014 and 4015, and the power line
can be separated or branched into the desired number of power lines
to be led to desired portions.
[0065] The first substrate 4001 and the second substrate 4006 are
substrates having insulating surfaces, and specifically, glass, a
metal (stainless-steel, typically), ceramics, plastic or the like
can be used. As plastic, an FRP (fiberglass-reinforced plastics)
sheet, a PVF (polyvinyl fluoride) film, a mylar film, a polyester
film, or an acrylic resin film can be used. In addition, a sheet in
which an aluminum foil is sandwiched by the PVF film or the mylar
film can also be used.
[0066] However, the substrate which is located on a side where
light from the light emitting element 4011 is emitted needs to have
a light-transmitting property. For example, in a case where light
is emitted through the second substrate 4006 side, the second
substrate 4006 needs to have a light-transmitting property. In that
case, a material with a light-transmitting property, such as a
glass plate, a plastic sheet, a polyester film, or an acrylic film
is used.
[0067] As the filler 4007, an ultraviolet curable resin or a
thermoset resin can be used, in addition to an inert gas such as
nitrogen or argon. Specifically, PVC (polyvinyl chloride), acrylic,
polyimide, an epoxy resin, a silicon resin, PVB (polyvinyl
butyral), EVA (ethylene vinyl acetate) or the like can be used. In
the present embodiment mode, nitrogen is used as the filler.
[0068] In this way, the light emitting device can be manufactured.
As described above, separate FPC terminals for power are used,
instead of sharing an FPC terminal for a power line with the same
potential between a logic portion and a buffer portion as in a
conventional case, or the power line is branched at a point close
to the FPC terminal, instead of sharing the power line with the
same potential between a logic portion and a buffer portion as in a
conventional case. By doing so, it becomes possible to reduce the
problem that the logic portion included in the light emitting
device is affected by noise and malfunctions, even when a voltage
of the power line drops and noise is generated.
[0069] The present embodiment mode can be freely combined with the
above-described embodiment modes.
(Embodiment Mode 4)
[0070] In the present embodiment mode, a structure of a light
emitting device is shown in a block diagram of FIG. 3A as an
example.
[0071] The light emitting device shown in FIG. 3A includes a panel
300, a controller 301, and a table 302 over an insulating surface.
In addition, the panel 300 includes a pixel portion 303 with pixels
each of which has a light emitting element, a source driver 304,
and a gate driver 305.
[0072] FIG. 3B is an example of a more specific structure of the
panel 300 shown in FIG. 3A. In FIG. 3B, the source driver 304
includes a logic portion 313 having a shift resister circuit 306, a
first latch circuit 307, and a second latch circuit 308; and a
buffer portion 314 having a level shifter circuit 311 and a buffer
circuit 312. It is to be noted that a circuit which can select a
signal line, such as a decoder, may be used instead of the shift
resister circuit 306.
[0073] The gate driver 305 includes a shift resister circuit 309
and a buffer circuit 310. The gate driver 305 may further include a
level shifter. It is to be noted that a circuit which can select a
signal line, such as a decoder, may be used instead of the shift
resister circuit 309.
[0074] In such a light emitting device, separate FPC terminals for
power are used, instead of sharing an FPC terminal for a power line
with the same potential between a logic portion and a buffer
portion as in a conventional case, or the power line is branched at
a point close to the FPC terminal, instead of sharing a power line
with the same potential between a logic portion and a buffer
portion as in a conventional case. By doing so, it becomes possible
to reduce the problem that the logic portion included in the light
emitting device is affected by noise and malfunctions, even when a
voltage of the power line drops and noise is generated.
Furthermore, the present invention can be applied to a shift
resister circuit and a latch circuit in a logic portion. As a
result, noise of a signal for display is reduced and a light
emitting device with less flickering can be provided.
(Embodiment Mode 5)
[0075] In the present embodiment mode, a circuit structure of the
above-described light emitting device will be described.
[0076] FIG. 9 shows an example of an equivalent circuit diagram of
a pixel, and a signal line 6114, a power line 6115, a scanning line
6116, a light emitting element 6113, transistors 6110 and 6111, and
a capacitative element 6112 are included. A video signal is
inputted to the signal line 6114 by a source driver. The transistor
6110 can control supply of a potential of the video signal to a
gate of the transistor 6111 in accordance with a selection signal
inputted to the scanning line 6116. The transistor 6111 can control
supply of a current to the light emitting element 6113 in
accordance with the potential of the video signal. The capacitative
element 6112 can maintain a voltage between a gate and a source of
the transistor 6111. It is to be noted that, although the
capacitative element 6112 is shown in FIG. 9, the capacitative
element 6112 is not necessarily provided in a case where its
function can be covered by gate capacitance of the transistor 6111
or other parasitic capacitance.
[0077] FIG. 10A is an equivalent circuit diagram of a pixel in
which a transistor 6118 and a scanning line 6119 are newly added to
the pixel shown in FIG. 9. Since a condition where no current flows
in the light emitting element 6113 can forcibly be made by the
transistor 6118 by making the gate and the source of the transistor
6111 have the same potential, a length of a sub-frame period can be
shorter than a period in which a video signal is inputted to all
the pixels. This is preferable when display of high gradation
number is performed while suppressing the drive frequency.
[0078] FIG. 10B is an equivalent circuit diagram of a pixel in
which a transistor 6125 and a wiring 6126 are newly added to the
pixel shown in FIG. 10A. A potential of a gate of the transistor
6125 is fixed by the wiring 6126. The transistor 6111 and the
transistor 6125 are connected in series between the power line 6115
and the light emitting element 6113. Accordingly, in FIG. 10B, a
value of a current to be supplied to the light emitting element
6113 is controlled by the transistor 6125, and whether or not the
current is supplied to the light emitting element 6113 can be
controlled by the transistor 6111.
[0079] In such a light emitting device, separate FPC terminals for
power are used, instead of sharing an FPC terminal for a power line
with the same potential between a logic portion and a buffer
portion as in a conventional case, or the power line is branched at
a point close to the FPC terminal, instead of sharing a power line
with the same potential between a logic portion and a buffer
portion as in a conventional case. By doing so, it becomes possible
to reduce the problem that the logic portion included in the light
emitting device is affected by noise and malfunctions, even when a
voltage of the power line drops and noise is generated.
Furthermore, the present invention can be applied to a shift
resister circuit and a latch circuit in a logic portion. As a
result, noise of a power line is reduced and a light emitting
device with less flickering can be provided.
[0080] It is to be noted that a pixel circuit included in a display
device of the present invention is not limited to the structure
shown in the present embodiment mode. In addition, the present
embodiment mode can be freely combined with the above-described
embodiment modes.
(Embodiment Mode 6)
[0081] In the present embodiment mode, an appearance of a mode of a
liquid crystal display device which is different from the
above-described embodiment mode will be described with reference to
FIGS. 11A and 11B. FIG. 11A is a top view of a panel which is
formed by sealing a TFT and a liquid crystal element formed over a
first substrate between the first substrate and a second substrate,
using a sealant in the same way as the above-described embodiment
mode. FIG. 11B corresponds to a cross-sectional view along a line
A-A' in FIG. 11A.
[0082] In the liquid crystal display device, the liquid crystal
element 4112 is sandwiched between a first substrate 4001 and a
second substrate 4006. The liquid crystal element 4112 controls
transmission of light from a backlight by a change in an
orientation condition made by a TFT 4009 in a pixel portion 4002
and an opposite electrode 4115 provided on the second substrate
4006 side, so that display can be performed. In order to align the
orientation of the liquid crystal element 4112, an orientation film
may be preferably provided for a surface to be connected to the
liquid crystal element 4112, that is, over the TFT 4009 and TFT
4008, and over the second substrate 4006. In addition, a color
filter may be provided for the first substrate 4001 or the second
substrate 4006, for full-color display.
[0083] In the same way as the above-described embodiment mode, an
FPC terminal 4016 is electrically connected to a terminal included
in an FPC 4018 via an anisotropic conductive film 4019. In
addition, as seen from the cross-sectional view in FIG. 11B, in a
power line separating portion 4020, a voltage is supplied from the
FPC terminal 4016 via the power lines 4014 and 4015 and the power
line can be separated or branched into the desired number of power
lines to be led to desired portions.
[0084] The structure other than this is similar to the
above-described embodiment mode, so that the explanation is omitted
here.
[0085] In this way, the liquid crystal display device can be
manufactured. As described above, separate FPC terminals for power
are used, instead of sharing an FPC terminal for a power line with
the same potential between a logic portion and a buffer portion as
in a conventional case, or the power line is branched at a point
close to the FPC terminal, instead of sharing a power line with the
same potential between a logic portion and a buffer portion as in a
conventional case. By doing so, it becomes possible to reduce the
problem that the logic portion included in the liquid crystal
display device is affected by noise and malfunctions, even when a
voltage of the power line drops and noise is generated.
[0086] The present embodiment mode can be freely combined with the
above-described embodiment modes.
(Embodiment Mode 7)
[0087] As described in the embodiment modes above, in the present
invention, in a case where the same potential is supplied to a
logic portion and a buffer portion, separate FPC terminals are used
for the logic portion and the buffer portion, or the FPC terminal
is shared but a power line is branched for the logic portion and
the buffer portion at a point close to the FPC terminal, so that a
problem such as a display defect caused by malfunction of a circuit
in the logic portion being affected by noise can be reduced, even
when noise is generated by a voltage drop of the power line due to
instantaneous high-current consumption in the buffer portion.
Therefore, the present invention can be preferably used for a
display portion of a battery-powered electronic device, a display
device with a large-sized screen, a display portion of an
electronic device, or the like. The following can be given as
examples: a television device (a TV or a television receiver), a
camera such as a digital camera or a digital video camera, a
cellular phone device (a cellular phone handset), a portable
information terminal such as PDA, a portable game machine, a
monitor, a computer, an audio reproducing device such as a car
audio, an image reproducing device provided with a recording medium
such as a home game machine, and the like. Specific examples
thereof will be described with reference to FIGS. 8A to 8F.
[0088] A portable information terminal device shown in FIG. 8A
includes a main body 9201, a display portion 9202, and the like. A
display device of the present invention can be applied to the
display portion 9202. As a result, a portable information terminal
device in which a problem such as a display defect caused by
malfunction of a circuit being affected by noise is reduced can be
provided.
[0089] A digital video camera shown in FIG. 8B includes a display
portion 9701, a display portion 9702, and the like. A display
device of the present invention can be applied to the display
portion 9701. As a result, a digital video camera in which a
problem such as a display defect caused by malfunction of a circuit
being affected by noise is reduced can be provided.
[0090] A cellular phone handset shown in FIG. 8C includes a main
body 9101, a display portion 9102, and the like. A display device
of the present invention can be applied to the display portion
9102. As a result, a cellular phone handset in which a problem such
as a display defect caused by malfunction of a circuit being
affected by noise is reduced can be provided.
[0091] A portable television device shown in FIG. 8D includes a
main body 9301, a display portion 9302, and the like. A display
device of the present invention can be applied to the display
portion 9302. As a result, a portable television device in which a
problem such as a display defect caused by malfunction of a circuit
being affected by noise is reduced can be provided. In addition,
the display device of the present invention can be widely applied
to various television devices such as a small-sized one
incorporated in a portable terminal such as a cellular phone
handset, a medium-sized one which is portable, and a large-sized
one (for example, 40 inches or more in size).
[0092] A laptop computer shown in FIG. 8E includes a main body
9401, a display portion 9402, and the like. A display device of the
present invention can be applied to the display portion 9402. As a
result, a laptop computer in which a problem such as a display
defect caused by malfunction of a circuit being affected by noise
is reduced can be provided.
[0093] A television device shown in FIG. 8F includes a main body
9501, a display portion 9502, and the like. A display device of the
present invention can be applied to the display portion 9502. As a
result, a television device in which a problem such as a display
defect caused by malfunction of a circuit being affected by noise
is reduced can be provided.
[0094] In this way, by applying a display device of the present
invention, electronic devices in which a problem such as a display
defect caused by malfunction of a circuit being affected by noise
is reduced can be provided.
[Embodiment]
[0095] In the present embodiment, an embodiment of the present
invention in a case where an example specification of the
above-described light emitting device is set to be as follows: a
display size, 2.0 inches; a pixel configuration, QVGA; the number
of pixels, 240.times.RGB.times.320; and a potential of a power
line, a low potential, that is, GND (0 V); will be described.
[0096] FIG. 4 is a simplified schematic showing an FPC terminal
portion for a ground (hereinafter referred to as GND) potential.
Although a power line or a signal line is led from other FPC
terminals than the FPC terminal for GND practically, a wiring led
from the other FPC terminals than the FPC terminal for GND is not
shown here in order to describe separation of a power line for GND
(hereinafter referred to as a GND line) led from the FPC terminal
for GND. Hereinafter, the FPC terminal portion for GND will be
described.
[0097] An FPC terminal portion 400 includes an FPC terminal 401 for
GND, another FPC terminal for power, and another FPC terminal for a
signal. For branching a first GND line 402 led from the FPC
terminal 401 for GND at a point close to the FPC terminal 401 for
GND, the first GND line 402 is connected to a second GND line 404
through a contact 403, and the second GND line 404 is connected to
a fourth GND line 408 for a buffer portion in a source driver
through a contact 410 and to a fifth GND line 409 for a logic
portion in the source driver through a contact 411; thereby
branching the GND line in each contact. That is, by connecting the
second GND line 404 to the fourth GND line 408 and the fifth GND
line 409 through the contacts, branching of the GND line can be
performed. A point where the GND line is branched can be set
according to a layout space or condition, but it needs to be far
from a circuit to be driven, that is, close to the FPC terminal 401
for GND. Specifically, branching is performed at a point of 1/3to
3/5of a length of the GND line extended from the FPC terminal to
the circuit. In addition, the GND line is also branched into a
sixth GND line 405, a seventh GND line 406, and a third GND line
407 for a gate driver, through a contact 412.
[0098] In the above-described way, one GND line is branched into
five lines to be led to desired circuits in FIG. 4, but the number
of branched GND lines is not limited to this. However, narrowing
the GND line too much to supply a sufficient current has to be
avoided. Branching of the GND line is performed in a scope which is
possible in operation of the circuit and in layout.
[0099] A width d1 of the fourth GND line 408 is set to be wider
than a width d2 of the fifth GND line 409 in FIG. 4. For example,
the width of the fourth GND line 408 may be 2 to 5 times that of
the fifth GND line 409, such as follows: the width of the fourth
GND line 408, 120 .mu.m; and the width of the fifth GND line 409,
40 .mu.m.
[0100] A reason why there is a difference in width between the GND
line connected to the logic portion and the GND line connected to
the buffer portion will be described. In the logic portion in which
a pulse is sequentially outputted according to a timing signal and
capture of data is performed, charging and discharging of many
nodes at a time is not often performed, so that instantaneous
high-current consumption does not occur. On the other hand, in the
buffer portion, such as a buffer portion performing line-sequential
driving specifically, data processing for one line is performed at
a time. That is, in the light emitting device shown in FIG. 3A and
3B, buffer circuits for 240.times.RGB columns perform charging and
discharging at a time. Therefore, in this moment, a high-current is
consumed, in other words, a high-current flows. For this reason,
the GND line for the buffer portion is led with a larger width than
a width of the GND line for the logic portion.
[0101] Next, a way of leading the GND line in the vicinity of a
logic portion 500 and a buffer portion 505 in a source driver will
be described. In FIG. 5, several power lines and various signal
lines are shown in addition to the fourth GND line 408 and the
fifth GND line 409.
[0102] The fifth GND line 409 is used as a GND line 508 for a shift
resister circuit 501 and a first latch circuit 503 in the logic
portion 500, and a GND line 509 for a second latch circuit 504.
[0103] In addition, the fourth GND line 408 is used as a GND line
for a level shifter circuit 506 and a buffer circuit 507 in the
buffer portion 505.
[0104] As described above, separate or branched power lines can be
used for the logic portion 500 as a low current consumption portion
in which a pulse is sequentially outputted according to desired
timing and capture of data or the like is performed, such as the
shift resister circuit 501, the first latch circuit 503, and the
second latch circuit 504; and the buffer portion 505 as a high
current consumption portion in which signal amplitude is amplified
and an instantaneous high-current is consumed, such as the buffer
circuit 507 and the level shifter circuit 506. As a result, the
conventional problem that a logic portion is affected by noise
generated by a voltage drop of a GND line in a buffer portion and
that the logic portion malfunctions, leading to a problem such as a
display defect, can be reduced.
[0105] This application is based on Japanese Patent Application
serial No. 2005-307856 filed in Japan Patent Office on Oct. 21st,
in 2005, the contents of which are hereby incorporated by
reference.
* * * * *