U.S. patent application number 14/568143 was filed with the patent office on 2015-04-09 for touch panel and driving method of the same.
The applicant listed for this patent is SEMICONDUCTOR ENERGY LABORATORY CO., LTD.. Invention is credited to Yoshiyuki KUROKAWA.
Application Number | 20150098031 14/568143 |
Document ID | / |
Family ID | 43380164 |
Filed Date | 2015-04-09 |
United States Patent
Application |
20150098031 |
Kind Code |
A1 |
KUROKAWA; Yoshiyuki |
April 9, 2015 |
TOUCH PANEL AND DRIVING METHOD OF THE SAME
Abstract
It is an object to provide a touch panel which includes an A/D
converter circuit and has a function of image shooting with high
resolution and high-level gray scale and at high operation speed. A
touch panel includes a plurality of pixels each provided with a
display element and a photo sensor, an A/D converter to which a
first potential is applied from a photo sensor, and a reading
circuit. The A/D converter includes an oscillation circuit which
changes the oscillating frequency of a first signal to be generated
in accordance with the first potential and stops oscillating when a
second potential is applied thereto from the reading circuit, and a
counter circuit which generates a second signal having a discrete
value determined in accordance with the oscillating frequency.
Inventors: |
KUROKAWA; Yoshiyuki;
(Sagamihara, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEMICONDUCTOR ENERGY LABORATORY CO., LTD. |
Atsugi-shi |
|
JP |
|
|
Family ID: |
43380164 |
Appl. No.: |
14/568143 |
Filed: |
December 12, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12816034 |
Jun 15, 2010 |
|
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14568143 |
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Current U.S.
Class: |
349/12 ;
250/206 |
Current CPC
Class: |
G06F 3/0412 20130101;
G06F 3/042 20130101; G06F 3/0416 20130101 |
Class at
Publication: |
349/12 ;
250/206 |
International
Class: |
G06F 3/042 20060101
G06F003/042 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2009 |
JP |
2009-150601 |
Jun 25, 2009 |
JP |
2009-150602 |
Claims
1. (canceled)
2. A semiconductor device comprising: a photo sensor; an
oscillation circuit operationally connected to the photo sensor;
and a counter circuit operationally connected to the photo sensor,
the counter circuit operationally connected to an output terminal
of the oscillation circuit, wherein the counter circuit is capable
of generating a first signal having a discrete value, wherein the
oscillation circuit is capable of generating a second signal having
an oscillation frequency, and wherein the discrete value is
determined by a signal from the photo sensor.
3. The semiconductor device according to claim 2, wherein the
second signal is determined by the signal from the photo
sensor.
4. The semiconductor device according to claim 2, wherein the
discrete value is determined by the oscillation frequency.
5. The semiconductor device according to claim 2, wherein a period
from when the oscillation circuit starts oscillating to when the
second signal has a toggle is approximately half an oscillation
cycle of the oscillation circuit.
6. The semiconductor device according to claim 2, wherein the photo
sensor comprises a photo diode.
7. The semiconductor device according to claim 2, further
comprising: a transistor including a semiconductor film, the
semiconductor film formed on a surface, wherein the photo sensor is
formed on the surface.
8. A touch panel comprising the semiconductor device according to
claim 2.
9. An electronic device comprising the touch panel according to
claim 8.
10. A semiconductor device comprising: a photo sensor; an
oscillation circuit operationally connected to the photo sensor;
and a counter circuit operationally connected to the photo sensor,
the counter circuit operationally connected to an output terminal
of the oscillation circuit, wherein the counter circuit is capable
of generating a first signal having a discrete value, wherein the
oscillation circuit is capable of generating a second signal having
an oscillation frequency, wherein the discrete value is determined
by a signal from the photo sensor, and wherein the photo sensor
includes a stacked structure vertically.
11. The semiconductor device according to claim 10, wherein the
second signal is determined by the signal from the photo
sensor.
12. The semiconductor device according to claim 10, wherein the
discrete value is determined by the oscillation frequency.
13. The semiconductor device according to claim 10, wherein a
period from when the oscillation circuit starts oscillating to when
the second signal has a toggle is approximately half an oscillation
cycle of the oscillation circuit.
14. The semiconductor device according to claim 10, wherein the
photo sensor comprises a photo diode.
15. The semiconductor device according to claim 10, further
comprising: a transistor including a semiconductor film, the
semiconductor film formed on a surface, wherein the photo sensor is
formed on the surface.
16. A touch panel comprising the semiconductor device according to
claim 10.
17. An electronic device comprising the touch panel according to
claim 16.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a touch panel including a
touch sensor and a driving method thereof. In particular, the
present invention relates to a touch panel in which pixels each
provided with a touch sensor are arranged in a matrix and a method
for driving the touch panel. Further, the present invention relates
to electronic devices including the touch panel.
[0003] 2. Description of the Related Art
[0004] In recent years, a display device provided with a touch
sensor has attracted attention. The display device provided with
the touch sensor is called a touch panel, a touch screen, and the
like (hereinafter simply referred to as a "touch panel"). Examples
of the touch sensor include a resistive touch sensor, a capacitance
touch sensor, and an optical touch sensor, which are different from
each other in operation principle. In any of the sensors, an object
to be detected is in contact with a display device or in the
vicinity of the display device, whereby data can be input.
[0005] By providing of a sensor (also referred to as a "photo
sensor") that detects light as an optical touch sensor for a touch
panel, a display screen serves as an input region. As an example of
a device including such an optical touch sensor, a display device
having an image capturing function, which is provided with a
contact area sensor that captures an image, is given (e.g., see
Patent Document 1). In the case of a touch panel including an
optical touch sensor, light is emitted from a touch panel. In the
case where an object to be detected exists at a given position of
the touch panel, light at the region where the object to be
detected exists is blocked by the object to be detected, and part
of light is reflected. A photo sensor (also referred to as a
"photoelectric conversion element") which can detect light is
provided in a pixel of the touch panel, and the photo sensor
detects the reflected light, so that the existence of the object to
be detected in the region where light is detected can be
recognized.
[0006] In addition, providing of a personal authentication function
or the like for an electronic device such as a mobile phone or a
portable information terminal has been attempted (for example, see
Patent Document 2). A finger print, a face, a hand print, a palm
print, a pattern of a hand vein, and the like are used for personal
authentication. In the case where a portion different from the
display portion has a personal authentication function, the number
of components increases, and the weight or price of the electronic
device could possibly increase.
[0007] In addition, in touch sensor systems, a technique for
selecting an image processing method by which the position of a
finger-tip is detected in accordance with brightness of external
light has been known (for example, see Patent Document 3).
REFERENCE
Patent Document
[0008] [Patent Document 1] Japanese Published Patent Application
No. 2001-292276
[0009] [Patent Document 2] Japanese Published Patent Application
No. 2002-033823
[0010] [Patent Document 3] Japanese Published Patent Application
No. 2007-183706
SUMMARY OF THE INVENTION
[0011] When a touch panel is used for an electronic device having a
personal authentication function, electrical signals which are
generated by photo sensors provided in respective pixels of the
touch panel by detecting light are collected and image processing
needs to be performed. In particular, a large amount of data
obtained by a number of photo sensors needs to be efficiently
collected in order to realize an electronic device with a personal
authentication function of high resolution and high-speed
operation. In addition, in order to realize a high degree of
personal authentication function, it is necessary to collect data
not in monochrome but in color, and further, with high-level gray
scale. In addition, since the electrical signals generated by photo
sensors are analog signals, conversion from an analog signal to a
digital signal (A/D conversion) is needed in order to perform image
processing. That is, an A/D converter circuit with high throughput
is required. However, if the circuit scale of the A/D converter
circuit is increased in order to achieve high throughput, a display
region of the touch panel becomes small. In addition, if power
consumption of the A/D converter circuit is increased in order to
achieve high throughput, power consumption of the touch panel is
also increased.
[0012] In view of the above problems, it is an object of one
embodiment of the disclosed invention to provide a touch panel
including an A/D converter circuit with smaller circuit scale and a
function of image shooting with high resolution and a driving
method thereof. It is an object of one embodiment of the disclosed
invention to provide a touch panel including an A/D converter
circuit with smaller circuit scale and a function of image shooting
with high-speed operation and a driving method thereof. It is an
object of one embodiment of the disclosed invention to provide a
touch, panel including an A/D converter circuit with smaller
circuit scale and a function of shooting with high-level gray scale
and a driving method thereof. Further, it is an object of one
embodiment of the present invention to provide a touch panel in
which power consumption can be suppressed and a driving method
thereof.
[0013] A first structure of a touch panel in one embodiment of the
present invention includes a display element and a photo sensor in
each pixel, an A/D converter corresponding to each of a plurality
of pixels, and a reading circuit of the photo sensor. The A/D
converter includes an oscillation circuit configured to change an
oscillation frequency in accordance with an output voltage
generated in the reading circuit and a counter circuit configured
to use an output signal from the oscillation circuit as a clock
signal. The discrete value of the counter circuit which is based on
the output voltage of the reading circuit is used as an output
value of the A/D converter. When the output value of the A/D
converter is determined, the output voltage of the reading circuit
is changed and oscillation of the oscillation circuit is stopped so
that the output value of the A/D converter is stabilized.
[0014] In addition, the touch panel in one embodiment of the
present invention has a structure in which an output signal does
not have a toggle when oscillation of the oscillation circuit stops
in addition to the first structure, so that output of the
oscillation circuit can be used as the least significant bit of an
output value of the A/D converter.
[0015] A second structure of a touch panel in one embodiment of the
present invention includes a display element and a photo sensor in
each pixel and an A/D converter corresponding to each of a
plurality of pixels. The A/D converter includes an oscillation
circuit configured to change an oscillation frequency in accordance
with an output voltage generated in a reading circuit of the photo
sensor and a counter circuit configured to use an output signal
from the oscillation circuit as a clock signal. The discrete value
of the counter circuit which is based on an output voltage of the
reading circuit is used as an output value of the A/D
converter.
[0016] In addition, the touch panel in one embodiment of the
present invention may further have a structure, in which the
oscillation circuit includes a latch circuit for storing a
potential of an output signal, in addition to the second structure.
When the output value of the A/D converter is determined, the
potential of the output signal of the oscillation circuit is stored
in the latch circuit and the clock signal of the counter circuit is
stopped, so that the output value of the A/D converter is
stabilized.
[0017] In addition, the touch panel in one embodiment of the
present invention may further have a structure in which an output
signal does not have a toggle when the output signal of the
oscillation circuit is stored in the latch circuit in addition to
the second structure, so that the output value of the oscillation
circuit can be used as the least significant bit of the output
value of the A/D converter.
[0018] The present invention can provide a touch panel which can
read images with high resolution and high-level gray scale at
high-speed and low power consumption while a display region is
secured. Alternatively, the present invention can provide a touch
panel which is capable of image reading of high resolution and
high-level gray scale at high speed and low power consumption and a
driving method thereof. Alternatively, the present invention can
provide a high-performance electronic device including the touch
panel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 illustrates a structure of a touch panel.
[0020] FIG. 2 illustrates a structure of a touch panel.
[0021] FIG. 3 illustrates a structure of a touch panel.
[0022] FIG. 4 illustrates a structure of a touch panel.
[0023] FIG. 5 illustrates a structure of a touch panel.
[0024] FIG. 6 illustrates a structure of a touch panel.
[0025] FIG. 7 illustrates a timing chart.
[0026] FIG. 8 illustrates a timing chart.
[0027] FIG. 9 illustrates a timing chart.
[0028] FIG. 10 illustrates a structure of a touch panel.
[0029] FIG. 11 illustrates a cross-sectional view of a touch
panel.
[0030] FIGS. 12A to 12E each illustrate an electronic device using
a touch panel.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Hereinafter, embodiments will be described in detail with
reference to the accompanying drawings. However, since embodiments
described below can be embodied in many different modes, it is
easily understood by those skilled in the art that the mode and the
detail can be variously changed without departing from the scope of
the present invention. Therefore, the present invention is not
interpreted as being limited to the description of the embodiments
below. In the drawings for explaining the embodiments, the same
parts or parts having a similar function are denoted by the same
reference numerals, and description of such parts is not
repeated.
Embodiment 1
[0032] In this embodiment, a touch panel will be described with
reference to FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5, FIG. 6, FIG.
7, FIG. 8, FIG. 9, and FIG. 10.
[0033] A structure of the touch panel will be described with
reference to FIG. 1. A touch panel 100 includes a pixel circuit
101, a display element control circuit 102, and a photo sensor
control circuit 103. The pixel circuit 101 includes a plurality of
pixels 104 arranged in a matrix of rows and columns. Each of the
pixels 104 includes a display element 105 and a photo sensor
106.
[0034] Each of the display elements 105 includes a thin film
transistor (TFT), a storage capacitor, a liquid crystal element
including a liquid crystal layer, a color filter, and the like.
Taking advantage of the change in the direction of a polarization
due to a voltage application to the liquid crystal layer, contrast
(gray scale) of light passing through the liquid crystal layer is
made, so that image display is realized. Outside light or light
from the rear side of a liquid crystal display device, which is
emitted by a light source (a backlight) is used as the light
passing through the liquid crystal layer. Further, the light which
has passed through the liquid crystal layer passes through a color
filter, so that a gray scale of a particular color (for example,
red (R), green (G), or blue (B)) can be produced and a color image
display is realized. The storage capacitor has a function of
holding a charge that corresponds to the voltage which is applied
to the liquid crystal layer. The thin film transistor has a
function of controlling injection or discharge of charge to the
storage capacitor.
[0035] Note that the case where each of the display elements 105
includes a liquid crystal element is described above; however,
other elements such as a light emitting element may be included
instead. The light emitting element is an element in which the
luminance is controlled by current or voltage. Specifically, light
emitting diode, OLED (organic light emitting diode), and the like
are given.
[0036] The photo sensor 106 includes an element such as a
photodiode, which has a function of generating an electrical signal
when receiving light, and a thin film transistor. Note that as
light which is received by the photo sensors 106, reflected light
or transmitted light obtained when outside light or light from a
backlight is delivered to an object to be detected can be used.
Here, the pixels 104 which emit light of colors of red (R), green
(G), and blue (B) by using a color filter are called an R pixel, a
G pixel, and a B pixel, respectively. Note that a red (R) color
component, a green (G) color component, and a blue (B) color
component in reflected light or transmitted light obtained when
outside light or light from a backlight is delivered to an object
to be detected can be detected by photo sensors in an R pixel, a G
pixel, and a B pixel, respectively.
[0037] The display element control circuit 102 controls the display
elements 105 and includes a display element driver circuit 107,
which inputs a signal to the display elements 105 through signal
lines (also referred to as source signal lines) such as video data
signal line, and a display element driver circuit 108 which inputs
a signal to the display elements 105 through scanning lines (also
referred to as gate signal lines). For example, the display element
driver circuit 108 on the scanning line side has a function of
selecting the display elements included in the pixels placed in a
particular line. Further, the display element driver circuit 107 on
the signal line side has a function of giving a predetermined
potential to the display elements 105 included in the pixels placed
in the selected line. Note that in the display elements 105 to
which the display element driver circuit 108 on the scanning line
side applies high potential, the thin film transistors are brought
into conduction and charges given by the display element driver
circuit 107 on the signal line side are supplied to the display
elements 105.
[0038] The photo sensor control circuit 103 controls the photo
sensors 106 and includes a photo sensor reading circuit 109 such as
a photo sensor output signal line and a photo sensor reference
signal line on the signal line side and a photo sensor driver
circuit 110 on the scanning line side. For example, the photo
sensor driver circuit 110 on the scanning line side has a function
of selecting the photo sensors 106 included in the pixels placed in
a predetermined line. Further, the photo sensor reading circuit 109
on the signal line side has a function of taking out an output
signal of the photo sensors 106 included in the pixels in the
selected line.
[0039] A circuit diagram of the pixel 104 will be described with
reference to FIG. 2. The pixel 104 includes the display element 105
including a transistor 201, a storage capacitor 202, and a liquid
crystal element 203, and the photo sensor 106 including a
photodiode 204, a transistor 205, and a transistor 206.
[0040] A gate of the transistor 201 is electrically connected to a
gate signal line 207, one of a source and a drain of the transistor
201 is electrically connected to a video data signal line 210, and
the other of the source and the drain of the transistor 201 is
electrically connected to one electrode of the storage capacitor
202 and one electrode of the liquid crystal element 203. The other
electrode of the storage capacitor 202 and the other electrode of
the liquid crystal element 203 are each held at a certain
potential. The liquid crystal element 203 is an element including a
pair of electrodes and a liquid crystal layer sandwiched between
the pair of electrodes.
[0041] When a potential at the High level "H" is applied to the
gate signal line 207, the transistor 201 applies the potential of
the video data signal line 210 to the storage capacitor 202 and the
liquid crystal element 203. The storage capacitor 202 holds the
applied potential. The liquid crystal element 203 changes light
transmittance in accordance with the applied potential.
[0042] One electrode of the photodiode 204 is electrically
connected to a photodiode reset signal line 208, and the other
electrode of the photodiode 204 is electrically connected to a gate
of the transistor 205. One of a source and a drain of the
transistor 205 is electrically connected to a photo sensor output
signal line 211, and the other of the source and the drain of the
transistor 205 is electrically connected to one of a source and a
drain of the transistor 206. A gate of the transistor 206 is
electrically connected to a gate signal line 209, and the other of
the source and the drain of the transistor 206 is electrically
connected to a photo sensor reference signal line 212.
[0043] Next, the structure of the photo sensor reading circuit 109
will be described with reference to FIG. 3.
[0044] The photo sensor reading circuit 109 includes a first A/D
converter (hereinafter referred to as a first ADC) 301 to a ninth
ADC 309; an ADC control circuit 310; a first spare reading circuit
341 to a ninth spare reading circuit 349; a first photo sensor
signal line 311 to a ninth photo sensor signal line 319; an output
signal line 320 of the photo sensor reading circuit 109; a first
ADC output signal line 321 to a ninth ADC output signal line 329; a
first ADC control signal line 331 to a ninth ADC control signal
line 339; and a first spare reading circuit control signal line 351
to a ninth spare reading circuit control signal line 359.
Specifically, the first photo sensor signal line 311 to the ninth
photo sensor signal line 319 are connected to the respective photo
sensor output signal lines 211 each included in the pixels 104 in
one column in the pixel circuit 101.
[0045] The ADC control circuit 310 generates a potential to be
output to the output signal line 320 of the photo sensor reading
circuit 109 based on the potential of each of the first ADC output
signal line 321 to the ninth ADC output signal line 329.
Specifically, one of the first ADC output signal line 321 to the
ninth ADC output signal line 329 is selected and the potential of
the selected signal line is output to the output signal line 320.
In addition, the ADC control circuit 310 generates a potential to
be output to each of the first ADC control signal line 331 to the
ninth ADC control signal line 339 and a potential output to each of
the first spare reading circuit control signal line 351 to the
ninth spare reading circuit control signal line 359.
[0046] Next, the structure and operation of the first ADC 301 to
the ninth ADC 309 will be specifically described. As a
representative example, a structure of the first ADC 301 will be
described below with reference to FIG. 4.
[0047] The first ADC 301 includes a voltage control oscillation
circuit (hereinafter referred to as a VCO) 401 and a counter
circuit 402. In the VCO 401, the cycle of a toggle of the potential
of an output signal at the High level "H" and the potential of the
output signal at the Low level "L" (the cycle of change from "H" to
"L" or "L" to "H") varies in accordance with the potential of the
first photo sensor signal line 311. An output signal from the VCO
401 is output to the output signal line 403. Here, half the number
of toggles per unit time is the oscillation frequency of the VCO
401. In addition, regardless of the potential of the first photo
sensor signal line 311, an output signal from the VCO 401 can have
a fixed value by a stop signal transmitted from a stop signal line
404. For example, when the stop signal is at "H", the output signal
can be at "L".
[0048] The counter circuit 402 operates using an output signal from
the VCO 401 as a clock signal. The discrete value of the counter
circuit 402 is increased in accordance with the oscillation
frequency of the VCO 401. The discrete value of the counter circuit
402 can be set to an initial value by a reset signal transmitted
from a reset signal line 405. For example, when the reset signal is
at "H", the initial value can be "0". In addition, the discrete
value of the counter circuit 402 is output as a digital value to
the first ADC output signal line 321 in accordance with a set
signal transmitted from a set signal line 406. For example, the
discrete value of the counter circuit 402 at the time of when the
level of the set signal is changed from "L" to "H" can be output as
a digital signal to the first ADC output signal line 321.
[0049] Note that the stop signal line 404, the reset signal line
405, and the set signal line 406 correspond to the first ADC
control signal line 331.
[0050] Here, if the oscillation frequency of the VCO 401 is low (or
high) when the potential of the first photo sensor signal line 311
is high (or low), the discrete value within a predetermined period
is small (or large) because the counter circuit 402 is operated by
a clock signal with a low (or high) frequency. Thus, a digital
value output to the first ADC output signal line 321 is small (or
large). In other words, the digital signal based on the potential
of the first photo sensor signal line 311 which is an analog value
is output; A/D conversion is performed.
[0051] Next, an example of the VCO 401 and the counter circuit 402
is described with reference to FIG. 5. The VCO 401 in FIG. 5
includes a NOR circuit 500, a first n-channel TFT 501 to a sixth
n-channel TFT 506, and a first p-channel TFT 507 to a twelfth
p-channel TFT 518. The lower the potential of the first photo
sensor signal line 311 becomes, the higher the oscillation
frequency of the VCO 401 in FIG. 5 becomes. In addition, when the
stop signal line 404 is set at "H", an output signal is at "L"
regardless of the potential of the first photo sensor signal line
311. Note that the first n-channel TFT 501, the first p-channel TFT
507, and the seventh p-channel TFT 513 constitute a first voltage
control NOT circuit. By controlling the gate voltage of the seventh
p-channel TFT 513 in accordance with the potential of the first
photo sensor signal line 311, the driving capability of the seventh
p-channel TFT 513 is changed, whereby a delay time in the first
voltage control NOT circuit is changed. Similarly, a second voltage
control NOT circuit to a sixth voltage control NOT circuit include
the second n-channel TFT 502 to the sixth n-channel TFT 506, the
second p-channel TFT 508 to the sixth p-channel TFT 512, and the
eighth p-channel TFT 514 to the twelfth p-channel TFT 518,
respectively.
[0052] Note that in FIG. 5, although the VCO 401 includes seven
stages of the NOR circuit 500 and the first voltage control NOT
circuit to the sixth voltage control NOT circuit, the VCO can have
a different number of stages as long as an odd number of stages are
provided. In addition, in the case where the VCO has a structure in
which the higher the potential of the first photo sensor signal
line 311 becomes, the higher the oscillation frequency of the VCO
becomes, a voltage control NOT circuit may have a structure in
which the gate voltage of an n-channel TFT is controlled in
accordance with the potential of the first photo sensor signal line
311. Further, by replacing the NOR circuit with a NAND circuit, a
VCO can have a structure in which an output signal is at "H" when
the stop signal line 404 is set at "L" regardless of the potential
of the first photo sensor signal line 311.
[0053] On the other hand, the counter circuit 402 in FIG. 5
includes a first reset flip-flop 519 to a fourth reset flip-flop
522, a first flip-flop 523 to a fourth flip-flop 526, and a first
NOT circuit 527 to a fourth NOT circuit 530. The first reset
flip-flop 519 to the fourth reset flip-flop 522 and the first NOT
circuit 527 to the fourth NOT circuit 530 constitute 4-bit
non-synchronous counter. Values in a zeroth bit to a third bit of
the discrete value of the non-synchronous counter are output to
signal lines 531 to 534. The discrete value of the non-synchronous
counter is set to an initial value of "0000" by setting the reset
signal line 405 at "H". In addition, the non-synchronous counter
operates using an output signal from the VCO 401 supplied through
the output signal line 403 as a clock signal.
[0054] When the level of the potential of the set signal line 406
is changed from "L" to "H", the discrete value of the
non-synchronous counter is stored in the first flip-flip 523 to the
fourth flip-flop 526 and is output to a zeroth bit signal line 535
to a third bit signal line 538 as a digital value. Note that the
zeroth bit signal line 535 to the third bit signal line 538
constitute the first ADC output signal line 321.
[0055] Note that in FIG. 5, although the counter circuit 402
includes the 4-bit non-synchronous counter and the 4-bit
flip-flops, a given number of bits can be employed for the counter
circuit. In addition, instead of the non-synchronous counter, a
synchronous counter can be employed. Since the number of flip-flops
which operate at high speed can be reduced with the use of the
non-synchronous counter, it is suitable for reduction in power
consumption. In addition, although a structure in which the
flip-flop configured to operate with a rising edge of a set signal,
that is, with a change of the level of the potential of the set
signal line 406 from "L" to "H" is employed in order to obtain the
discrete value of a counter, a structure in which the flip-flop
which operate with a falling edge can be employed. Alternatively, a
structure in which a level sensitive latch operates when the set
signal is at "H" or "L" may be employed.
[0056] Next, a structure of the first spare reading circuit 341 to
the ninth spare reading circuit 349 is described. The structure of
the first spare reading circuit 341 is described below as a typical
example with reference to FIG. 6. The first spare reading circuit
341 illustrated in FIG. 6 includes a p-channel TFT 601 and a
storage capacitor 602.
[0057] In the first spare reading circuit 341, the potential of the
photo sensor signal line is set to a reference potential before
operation of a photo sensor in a pixel. In FIG. 6, by setting the
first spare reading circuit control signal line 351 at "L", the
first photo sensor signal line 311 can be set to have a high
potential which is a reference potential. Note that the storage
capacitor 602 is not necessarily provided in the case where the
parasitic capacitance of the first photo sensor signal line 311 is
high. Note that the reference potential can be a low potential. In
that case, an n-channel TFT is used instead of the p-channel TFT
601 and the first spare reading circuit control signal line 351 is
set at "H", whereby the first photo sensor signal line 311 can be
set to have a low potential which is a reference potential.
[0058] Next, reading operation of a photo sensor in this touch
panel is described with reference to a timing chart in FIG. 7. In
FIG. 7, a signal 701 corresponds to the potential of the photodiode
reset signal line 208; a signal 702 corresponds to the potential of
the gate signal line 209 to which the gate of the transistor 206 is
connected; a signal 703 corresponds to the potential of a gate
signal line 213 to which the gate of the transistor 205 is
electrically connected; and a signal 704 corresponds to the
potential of the photo sensor output signal line 211 in FIG. 2. In
addition, the signal 705 corresponds to the potential of the spare
reading circuit control signal line 351 in FIG. 6. Further, signals
706 to 717 correspond to the potential of the stop signal line 404,
the potential of the output signal line 403 of the VCO, the
potential of the reset signal line 405, the potential of the signal
line 531, the potential of the signal line 532, the potential of
the signal line 533, the potential of the signal line 534, the
potential of the set signal line 406, the potential of the zeroth
signal line 535, the potential of the first signal line 536, the
potential of the second signal line 537, and the potential of the
third bit signal line 538 in FIG. 5, respectively.
[0059] Here, the case where light delivered to a photodiode is more
intense in a second period 722 than that in a first period 721 is
described. Note that the oscillation cycles of the VCO 401 are TV
CO1 and TV CO2 in the first period 721 and the second period 722,
respectively. Thus, the oscillation frequencies are 1/TVCO1 and
1/TVCO2 in the first period 721 and the second period 722,
respectively. Here, TVCO1 is longer than TVCO2.
[0060] First, the first period 721 is described. In a time A1, when
the potential of the photodiode reset signal line 208 (signal 701)
is at "H", the photodiode 204 is brought into conduction and the
potential of the gate signal line 213 (signal 703) to which the
gate of the transistor 205 is connected is at "H". In addition,
when the potential of the spare reading circuit control signal line
351 (signal 705) is at "L", the potential of the photo sensor
output signal line 211 (signal 704) is precharged with "H".
[0061] In a time B1, when the potential of the photodiode reset
signal line 208 (signal 701) is at "L", the potential of the gate
signal line 213 to which the gate of the transistor 205 is
connected (signal 703) is lowered because of off current of the
photodiode 204. The off current of the photodiode 204 increases
when light is delivered to the photodiode 204; therefore, the
potential of the gate signal line 213 to which the gate of the
transistor 205 is connected (signal 703) varies in accordance with
the amount of the light delivered to the photodiode 204. That is,
current between a source and a drain of the transistor 205
varies.
[0062] In a time C1, when the potential of the gate signal line 209
(signal 702) is at "H", the transistor 206 is brought into
conduction and electrical continuity is established between the
photo sensor reference signal line 212 and the photo sensor output
signal line 211 through the transistor 205 and the transistor 206.
Then, the potential of the photo sensor output signal line 211
(signal 704) is decreased. Note that before the time C1, the
potential of the spare reading circuit control signal line 351
(signal 705) is set at "H" and precharge of the photo sensor output
signal line 211 is completed. Here, the rate at which the potential
of the photo sensor output signal line 211 (signal 704) decreases
depends on the current between the source and the drain of the
transistor 205. That is, the rate of decreasing the potential of
the photo sensor output signal line 211 varies in accordance with
the amount of light which is delivered to the photodiode 204.
[0063] In a time D1, when the potential of the gate signal line 209
(signal 702) is at "L", the transistor 206 is turned off, whereby
the potential of the photo sensor output signal line 211 (signal
704) is kept at a fixed value after the time D1.
[0064] In a time E1, when the potential of the stop signal line 404
(signal 706) is set from "H" to "L", the VCO 401 start oscillating
at an oscillation frequency which is based on the potential of the
photo sensor output signal line 211 (signal 704) and the output
signal becomes like a signal 707.
[0065] In a time F1, when the potential of the reset signal line
405 (signal 708) is set from "H" to "L", the non-synchronous
counter starts counting. Note that when the potential of the reset
signal line 405 is at "H", the non-synchronous counter is set to
the initial value "0000"; therefore, the potentials of the signal
lines 531 to 534 (signal 709 to 712) are all set to "L". Note that
by making timing of when the potential of the reset signal line 405
(signal 708) is set from "H" to "L" come at the same time as or
earlier than timing of when the potential of the stop signal line
404 (signal 706) is set from "H" to "L", a period during which the
non-synchronous counter counts can be made longer. Therefore, an
ADC with a high throughput can be achieved, which is
preferable.
[0066] In a time G1, when the potential of the set signal line 406
(signal 713) is set from "L" to "H", the discrete values of the
non-synchronous counter, that is, the values of the signal lines
531 to 534 are stored in the first flip-flop 523 to the fourth
flip-flop 526, whereby the potentials of the zeroth bit signal line
535 to the third bit signal line 538 (signals 714 to 717) vary.
Here, the potentials of the zeroth bit signal line 535 to the third
bit signal line 538 are "H", "H", "H", and "L", respectively. They
are "7" in decimal notation.
[0067] Next, the second period 722 is described. Signals in times
A2, B2, C2, D2, E2, and F2 differ from the signals in the times A1,
B1, C1, D1, E1, and F1 in the intensity of light delivered to the
photodiode. Specifically, since the intensity of light in the
second period 722 is high, the potential of the gate signal line
213 to which the gate of the transistor 205 is connected (signal
703) is reduced more quickly after the time B2 than that after the
time B1. Thus, the potential of the photo sensor output signal line
211 (signal 704) in the time D2 is lower than that in the time D1.
Therefore, the oscillation frequency of the output signal of the
VCO 401 (signal 707) after the time E2 is higher than that after
the time E1.
[0068] On the other hand, in the time G2, when the potential of the
set signal line 406 (signal 713) is set from "L" to "H", the
discrete values of the non-synchronous counter, that is, the values
of the signal lines 531 to 534 are stored in the first flip-flop
523 to the fourth flip-flop 526, whereby the potentials of the
zeroth bit signal line 535 to the third bit signal line 538
(signals 714 to 717) vary. Here, the potentials of the zeroth bit
signal line 535 to the third bit signal line 538 are "L", "L", "L",
and "L", respectively. They are "0" in decimal notation.
[0069] Thus, although light delivered to the photodiode is intense,
an output value of the ADC in the second period 722 is smaller than
that in the first period 721, which is incoherence. A cause of such
malfunction can be described below. In the case of the structure
illustrated in FIG. 5, a clock signal that drives the
non-synchronous counter, that is, the output signal of the VCO 401
(signal 707) does not synchronize with the set signal supplied from
the set signal line 406 (signal 713). Therefore, there is a
possibility that the discrete values of the non-synchronous counter
are stored in the first flip-flop 523 to the fourth flip-flop 526
while the discrete values are changing. In that case, wrong data is
output to the first ADC output signal line 321.
[0070] In view of this, a first structure according to one
embodiment of the present invention discloses the following driving
method: the photo sensor output signal line 211 is precharged just
before the discrete values of the non-synchronous counter are
stored in the first flip-flop 523 to the fourth flip-flop 526. The
driving method is described with reference to FIG. 8.
[0071] FIG. 8 is different from FIG. 7 in that the potential of the
spare reading circuit control signal line 351 (signal 805) is set
at "L" and the photo sensor output signal line 211 is precharged in
a time H1 and a time H2. At that time, the potential of the photo
sensor output signal line 211 is similar to that of a signal 804.
When the photo sensor output signal line 211 is precharged, the
oscillation of the VCO 401 stops; thus, the potential of the output
signal line 403 is kept as a value just before the time H1 and the
time H2 like the signal line 807.
[0072] Next, in the time G1 and the time G2, the potential of the
set signal line 406 (signal 713) is set from "L" to "H" and the
discrete value of the non-synchronous counter, that is, the
potentials of the signal lines 531 to 534 (signals 809 to 812) are
stored in the first flip-flop 523 to the fourth flip-flop 526. In
the first period 721, the potentials of the zeroth bit signal line
535 to the third bit signal line 538 (signals 814 to 817) are "L",
"H", "H", and "L", respectively. They are "6" in decimal notation.
On the other hand, in the second period 722, the potentials of the
zeroth bit signal line 535 to the third bit signal line 538
(signals 814 to 817) are "H", "H", "H", and "L", respectively. They
are "7" in decimal notation. That is, an output value of the ADC in
the second period 722 in which light delivered to photo diode is
intense is smaller than that in the first period 721, which means
that a correct result is obtained.
[0073] Alternatively, a second structure according to one
embodiment of the present invention discloses a driving method
illustrated in FIG. 10. A latch signal line 900 is additionally
provided for the first ADC 301. Note that the latch signal line
900, the stop signal line 404, the reset signal line 405, and the
set signal line 406 correspond to the first ADC control signal line
331. In addition, a latch circuit 901 is additionally provided for
the VCO 401. Here, an example in which the latch circuit 901
includes an analog switch 902, a clocked inverter 903, an inverter
904, and an inverter 905 is illustrated.
[0074] When the potential of the latch signal line 900 is at "H",
the latch circuit 901 outputs the potential of the signal line 906
as the potential of the output signal line 403. In addition, when
the potential of the latch signal line 900 is "L", as the potential
of the output signal line 403, the latch circuit 901 outputs the
potential of the signal line 906 at the time of when the potential
of the latch signal line 900 is set from "H" to "L".
[0075] Here, the potential of the latch signal line 900 is set at
"L" just before the discrete values of the non-synchronous counter
are stored in the first flip-flop 523 to the fourth flip-flop 526.
The driving method is described with reference to FIG. 9. Since
signals in FIG. 9 are similar to the signals 701 to 705 to in FIG.
7, they are omitted. In addition, FIG. 9 includes the potential of
the latch signal line 900 (signal 800) and the potential of the
signal line 906 (signal 801) added to the chart in FIG. 7.
[0076] In FIG. 9, the potential of the latch signal line (signal
800) is set at "H" before the time E1 and the time E2, i. e.,
before the potential of the stop signal line 404 (signal 706) is
set from "H" to "L" and the VCO 401 oscillates.
[0077] Next, by setting the potential of the latch signal line 900
(signal 800) at "L" in the time H1 and the time H2, the potential
of the output signal line 403 (signal 807) is kept as the same
value as the potential of the signal line 906 (signal 801) just
before the time H1 and the time H2.
[0078] Next, in the time G1 and the time G2, the potential of the
set signal line 406 (signal 713) is set from "L" to "H" and the
discrete value of the non-synchronous counter, that is, the
potentials of the signal lines 531 to 534 (signals 809 to 812) are
stored in the first flip-flop 523 to the fourth flip-flop 526. In
the first period 721, the potentials of the zeroth bit signal line
535 to the third bit signal line 538 (signals 814 to 817) are "L",
"H", "H", and "L", respectively. They are "6" in decimal notation.
On the other hand, in the second period 722, the potentials of the
zeroth bit signal line 535 to the third bit signal line 538
(signals 814 to 817) are "H", "H", "H", and "L", respectively. They
are "7" in decimal notation. That is, an output value of the ADC in
the second period 722 in which light delivered to photo diode is
intense is smaller than that in the first period 721, which means
that a correct result is obtained.
[0079] Note that by employing the driving method illustrated by the
timing chart in FIG. 8 or FIG. 9, an output signal of the VCO 401
can be used as the least significant bit of the non-synchronous
counter. In that case, since the number of bits can be increased
without providing an additional circuit, an ADC with high accuracy
and low power consumption can be achieved, which is preferable.
Further, by making timing of when the potential of the reset signal
line 405 (signal 708 in FIG. 8 or FIG. 9) is set from "H" to "L"
come at the same time as or earlier than timing of when the
potential of the stop signal line 404 (signal 706 in FIG. 8 or FIG.
9) is set from "H" to "L", the least significant bit, that is, an
output signal of the VCO 401 is set at "L" as an initial value and
set at "H" after approximately half a cycle (TVCO/2); therefore,
accuracy of the ADC can be increased.
[0080] In one embodiment of the present invention, since the A/D
converter including the VCO and the counter circuit is used, a
circuit scale can be made small as compared to the case where a
successive-comparison type A/D converter including a comparison
circuit, a register circuit, and a D/A converter circuit is used,
for example. In other words, a display region of a touch panel can
be secured. In addition, in the case where on output of the VCO is
used as the least significant bit of the counter, the A/D converter
with low power consumption and a high throughput can be
achieved.
[0081] Therefore, a touch panel can be provided which is capable of
image reading of high resolution and high-level gray scale at high
speed with low power consumption while a display region is secured.
In addition, a driving method of a touch panel of high performance
can be provided.
Embodiment 2
[0082] In this embodiment, a cross-sectional structure of a touch
panel in one embodiment of the present invention is described.
[0083] FIG. 11 illustrates an example of a cross-sectional view of
the touch panel. In the touch panel illustrated in FIG. 11, a
photodiode 1002, a transistor 1003, a storage capacitor 1004, and a
liquid crystal element 1005 are formed over a substrate 1001 having
an insulating surface.
[0084] The photodiode 1002 and the storage capacitor 1004 can be
formed at the same time as the transistor 1003 is formed in a
manufacturing process of the transistor 1003. The photodiode 1002
is a lateral junction pin diode. A semiconductor film 1006 included
in the photo diode 1002 has a region having p-type conductivity (p
layer), a region having i-type conductivity (i layer), and a region
having n-type conductivity (n layer). Note that although the case
where the photodiode 1002 is a pin diode is illustrated in this
embodiment, the photodiode 1002 may be a pn diode. With lateral pin
junction or lateral pn junction, an impurity imparting p-type
conductivity and an impurity imparting n-type conductivity can be
added to respective particular regions in the semiconductor film
1006.
[0085] In addition, although the case where the photo diode 1002 is
a lateral junction diode in which a p layer and an n layer are
formed in different regions is illustrated, the photodiode 1002 may
be a vertical-junction diode in which a p layer and an n layer
overlap with each other in direction perpendicular to the substrate
1001. The vertical pin junction can be obtained by stacking a
semiconductor film having p-type conductivity, a semiconductor film
having i-type conductivity, and a semiconductor film having n-type
conductivity. Similarly, vertical pn junction can be obtained by
stacking a semiconductor film having p-type conductivity and a
semiconductor film having n-type conductivity.
[0086] The liquid crystal element 1005 includes a pixel electrode
1007, liquid crystals 1008, and a counter electrode 1009. The pixel
electrode 1007 is formed over the substrate 1001 and is
electrically connected to the transistor 1003 through the storage
capacitor 1004 and a conductive film 1010. In addition, the counter
electrode 1009 is formed on the substrate 1013 and the liquid
crystals 1008 are interposed between the pixel electrode 1007 and
the counter electrode 1009. Note that although a transistor used
for a photo sensor is not illustrated in this embodiment, the
transistor can be formed over the substrate 1001 together with the
transistor 1003 in the manufacturing process for the transistor
1003.
[0087] A cell gap between the pixel electrode 1007 and the counter
electrode 1009 can be controlled by using a spacer 1016. In FIG.
11, the cell gap is controlled by using the columnar spacer 1016
selectively formed by photolithography. Alternatively, the cell gap
can be controlled by dispersing spherical spacers between the pixel
electrode 1007 and the counter electrode 1009.
[0088] In addition, the liquid crystals 1008 are surrounded by a
sealing material between the substrate 1001 and the substrate 1013.
The liquid crystals 1008 may be injected by a dispenser method
(droplet method) or a dipping method (pumping method).
[0089] For the pixel electrode 1007, a light-transmitting
conductive material such as indium tin oxide (ITO), indium tin
oxide containing silicon oxide (ITSO), organic indium, organic tin,
indium zinc oxide (IZO) containing zinc oxide (ZnO), zinc oxide
(ZnO), ZnO containing gallium (Ga), tin oxide (SnO.sub.2), indium
oxide containing tungsten oxide, indium zinc oxide containing
tungsten oxide, indium oxide containing titanium oxide, indium tin
oxide containing titanium oxide, or the like can be used.
[0090] In addition, since the transparent liquid crystal element
1005 is given as an example, the above-described light-transmitting
conductive material can be used also for the counter electrode 1009
like in the case of the pixel electrode 1007.
[0091] An alignment film 1011 is provided between the pixel
electrode 1007 and the liquid crystals 1008 and an alignment film
1012 is provided between the counter electrode 1009 and the liquid
crystals 1008. The alignment film 1011 and the alignment film 1012
can be formed using an organic resin such as polyimide or polyvinyl
alcohol. An alignment treatment such as rubbing is performed on
their surfaces in order to align liquid crystal molecules in
certain direction. Rubbing can be performed by rolling a roller
wrapped with cloth of nylon or the like while applying pressure on
the alignment film so that the surface of the alignment film is
rubbed in certain direction. Note that by using an inorganic
material such as silicon oxide, the alignment film 1011 and the
alignment film 1012 each having an alignment property can be
directly formed by evaporation method without performing an
alignment treatment.
[0092] Further, a color filter 1014 which can pass light in a
certain wavelength range is formed over the substrate 1013 so as to
overlap with the liquid crystal element 1005. The color filter 1014
can be selectively formed by photolithography after application of
an organic resin such as an acrylic-based resin in which colorant
is dispersed on the substrate 1013. Alternatively, color filter
1014 can be selectively formed by etching after application of a
polyimide-based resin in which colorant is dispersed on the
substrate 1013. Alternatively, the color filter 1014 can be
selectively formed by a droplet discharge method such as an ink jet
method.
[0093] Furthermore, a shielding film 1015 which can block light is
formed over the substrate 1013 so as to overlap with the photodiode
1002. By providing of the shielding film 1015, light from a
backlight that passes through the substrate 1013 and enters the
touch panel can be prevented from being directly delivered to the
photodiode 1002. Further, disclination due to disorder of alignment
of the liquid crystals 1008 among pixels can be prevented from
being viewed. An organic resin containing black colorant such as
carbon black or titanium lower oxide in which the number of oxides
is smaller than that of titanium dioxide can be used for the
shielding film 1015. Alternatively, a film of chromium can be used
for the shielding film 1015.
[0094] Furthermore, a polarizing plate 1017 is provided on a
surface which is the reverse side of a surface of the substrate
1001 over which the pixel electrode 1007 is formed and a polarizing
plate 1018 is provided on a surface which is the reverse side of a
surface of the substrate 1013 over which the counter electrode 1009
is formed.
[0095] Light from the backlight passes through the liquid crystal
element 1005 and is delivered to an object 1021 to be detected on
the substrate 1001 side as shown by an arrow 1020. Then, light
reflected by the object 1021 to be detected enters the photodiode
1002 as shown by an arrow 1022.
[0096] The liquid crystal element may be a TN (twisted nematic)
mode liquid crystal element, a VA (vertical alignment) mode liquid
crystal element, an OCB (optically compensated birefringence) mode
liquid crystal element, an IPS (in-plane switching) mode liquid
crystal element, or the like. Note that although an example of the
liquid crystal element 1005 in which the liquid crystals 1008 are
interposed between the pixel electrode 1007 and the counter
electrode 1009 is given in this embodiment, the touch panel in one
embodiment of the present invention is not limited to this
structure. A liquid crystal element in which a pair of electrodes
are formed on the substrate 1001 side like an IPS mode liquid
crystal element may also be employed.
[0097] In addition, although an example in which a thin
semiconductor film is used for the photodiode 1002, the transistor
1003, and the storage capacitor 1004 is illustrated in this
embodiment, a single crystal semiconductor substrate, an SOI
substrate, or the like can be used for the photodiode 1002, the
transistor 1003, and the storage capacitor 1004.
Example 1
[0098] The touch panel in one embodiment of the present invention
has a characteristic of image reading of high resolution and
high-level gray scale at high speed and with low power consumption.
Therefore, an electronic device using the touch panel in one
embodiment of the present invention can be provided with
applications with higher performance by employing a touch panel as
its component. In particular, in the case of a portable electronic
device which cannot be constantly supplied with electric power, by
employing a touch panel as its component, an advantage that
continuous operating time is made longer can be obtained in
addition to an advantage that the portable electronic device can be
provided with applications with higher performance. The touch panel
in the present invention can be included in display devices, laptop
computers, and image reproducing devices provided with recording
media (typically devices which reproduce the content of recording
media such as DVDs (digital versatile disc) and have displays for
displaying the reproduced images). Other than above, as an
electronic device which can use the touch panel in one embodiment
of the present invention, mobile phones, portable game machines,
portable information terminals, e-book readers, video cameras,
digital still cameras, goggle-type displays (head mounted
displays), navigation systems, audio reproducing devices (e.g., car
audio components and audio components), copiers, facsimiles,
printers, multifunction printers, automated teller machines (ATM),
vending machines, and the like can be given. FIGS. 12A to 12E
illustrate specific examples of these electronic devices.
[0099] FIG. 12A illustrates a display device including a housing
5001, a display portion 5002, a supporting base 5003, and the like.
The touch panel in one embodiment of the present invention can be
used for the display portion 5002. By using the touch panel in one
embodiment of the present invention for the display portion 5002,
image reading of high resolution and high-level gray scale can be
performed at high speed and with low power consumption and a
display device with applications of higher performance can be
provided. Note that a display device includes all display devices
for displaying information, such as display devices for personal
computers, for receiving television broadcast, and for displaying
advertisement, in its category.
[0100] FIG. 12B illustrates a portable information terminal
including a housing 5101, a display portion 5102, a switch 5103, an
operation key 5104, an infrared rays port 5105, and the like. The
touch panel in one embodiment of the present invention can be used
for the display portion 5102. By using the touch panel in one
embodiment of the present invention for the display portion 5102,
image reading of high resolution and high-level gray scale can be
performed at high speed and with low power consumption and a
portable information terminal with applications of higher
performance can be provided.
[0101] FIG. 12C illustrates an automated teller machine including a
housing 5201, a display portion 5202, a coin slot 5203, a bill slot
5204, a card slot 5205, a bankbook slot 5206, and the like. The
touch panel in one embodiment of the present invention can be used
for the display portion 5202. By using the touch panel in one
embodiment of the present invention for the display portion 5202,
image reading of high resolution and high-level gray scale can be
performed at high speed and with low power consumption and an
automated teller machine with applications of higher performance
can be provided. The automated teller machine using the touch panel
in one embodiment of the present invention can read information of
living body such as a finger print, a face, a handprint, a palm
print, a pattern of a hand vein, an iris, and the like which are
used for biometrics with higher accuracy. Therefore, a false
non-match rate which is false recognition of a person to be
identified as a different person and a false acceptance rate which
is false recognition of a different person as a person to be
identified can be suppressed.
[0102] FIG. 12D illustrates a portable game machine including a
housing 5301, a housing 5302, a display portion 5303, a display
portion 5304, a microphone 5305, speakers 5306, an operation key
5307, a stylus 5308, and the like. The touch panel in one
embodiment of the present invention can be used for the display
portion 5303 or the display portion 5304. By using the touch panel
in one embodiment of the present invention for the display portion
5303 or the display portion 5304, image reading of high resolution
and high-level gray scale can be performed at high speed and with
low power consumption and a portable game machine with applications
of higher performance can be provided. Note that although the
portable game machine illustrated in FIG. 12D includes two display
portions 5303 and 5304, the number of display portions included in
the portable game machine is not limited to two.
[0103] FIG. 12E illustrates an electronic black board which
includes a housing 5401, a drawing portion 5402, and the like.
Information such as texts or drawings can be written on the drawing
portion 5402 of the electronic black board with the stylus 5403, a
marker using oil-based ink, or the like. Further, the electronic
black board can make information written on the drawing portion
5402 electronic data by using a photo sensor. In the case of using
the stylus 5403, the information written on the drawing portion
5402 is made electronic data by the photo sensor and then displayed
on the drawing portion 5402 by a display element. The touch panel
in one embodiment of the present invention can be used for the
drawing portion 5402. By using the touch panel in one embodiment of
the present invention for the drawing portion 5402, image reading
of high resolution and high-level gray scale can be performed at
high speed and with low power consumption and an electronic black
board with applications of higher performance can be provided.
[0104] This embodiment can be implemented by being combined as
appropriate with any of the aforementioned embodiments and
example.
[0105] This application is based on Japanese Patent Application
serial no. 2009-150602 filed with Japan Patent Office on Jun. 25,
2009, the entire contents of which are hereby incorporated by
reference.
* * * * *