U.S. patent application number 15/473017 was filed with the patent office on 2018-02-22 for electrostatic pen.
The applicant listed for this patent is Wacom Co., Ltd.. Invention is credited to Tomohiro Kagami, Yasuo Oda.
Application Number | 20180052532 15/473017 |
Document ID | / |
Family ID | 56542697 |
Filed Date | 2018-02-22 |
United States Patent
Application |
20180052532 |
Kind Code |
A9 |
Kagami; Tomohiro ; et
al. |
February 22, 2018 |
ELECTROSTATIC PEN
Abstract
An electrostatic pen has a switch, control circuitry to control
the switch and a pen point electrode. The switch has first, second
and third terminals and a first diode having an anode coupled to
the first terminal and a cathode coupled to the third terminal. The
pen point electrode is coupled to the first terminal of the switch.
The control circuitry, in operation, supplies respective potentials
to the second terminal and the third terminal of the switch and
switches between two or more states including a first state in
which a potential of the second terminal is higher than a potential
of the third terminal and a second state in which the potential of
the second terminal is equal to or lower than the potential of the
third terminal.
Inventors: |
Kagami; Tomohiro; (Tokyo,
JP) ; Oda; Yasuo; (Saitama, JP) |
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Applicant: |
Name |
City |
State |
Country |
Type |
Wacom Co., Ltd. |
Saitama |
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JP |
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Prior
Publication: |
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Document Identifier |
Publication Date |
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US 20170220138 A1 |
August 3, 2017 |
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Family ID: |
56542697 |
Appl. No.: |
15/473017 |
Filed: |
March 29, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/JP2015/052447 |
Jan 29, 2015 |
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15473017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06F 3/0446 20190501;
G06F 3/0441 20190501; G06F 3/03545 20130101; G06F 3/0383 20130101;
G06F 3/0442 20190501; G06F 3/044 20130101 |
International
Class: |
G06F 3/038 20060101
G06F003/038; G06F 3/0354 20060101 G06F003/0354 |
Claims
1. An electrostatic pen, comprising: a switch having: first, second
and third terminals; and a first diode having an anode coupled to
the first terminal and a cathode coupled to the third terminal; a
pen point electrode coupled to the first terminal of the switch;
and control circuitry, which, in operation: supplies respective
potentials to the second terminal and the third terminal of the
switch; and switches between two or more states including a first
state in which a potential of the second terminal is higher than a
potential of the third terminal and a second state in which the
potential of the second terminal is equal to or lower than the
potential of the third terminal.
2. The electrostatic pen according to claim 1 wherein the switch
includes a reverse-current limiting circuit coupled between the
first terminal and the second terminal, and, in operation, the
reverse-current limiting circuit limits a current from flowing
between the first terminal and the second terminal.
3. The electrostatic pen according to claim 2 wherein the
reverse-current limiting circuit comprises a resistive element.
4. The electrostatic pen according to claim 3 wherein the
reverse-current limiting circuit comprises a second diode having an
anode coupled to the resistive element and having a cathode coupled
to the first terminal.
5. The electrostatic pen according to claim 1 wherein the control
circuitry, in operation, supplies a control signal to the second
terminal.
6. The electrostatic pen according to claim 5 wherein the control
signal is a binary signal, which, in operation, has a value of one
of a high level and a low level.
7. The electrostatic pen according to claim 5 wherein the control
circuitry, in operation, supplies an inverted signal of the control
signal to the third terminal.
8. The electrostatic pen according to claim 7 wherein the control
circuitry, in operation, controls a potential difference between
the control signal and the inverted signal to have one of two or
more levels.
9. The electrostatic pen according to claim 8 wherein the control
circuitry, in operation, controls the potential difference between
the control signal and the inverted signal to have one of two or
more levels in a non-positive range of the first diode.
10. The electrostatic pen according to claim 1 wherein the third
terminal is coupled to a ground.
11. The electrostatic pen according to claim 10, comprising: a main
body comprising a conductor, the main body supporting the pen point
electrode via an insulator, wherein the third terminal is coupled
to the conductor and the conductor, in operation, is grounded
through user contact with the main body.
12. The electrostatic pen according to claim 1 wherein the first
diode is a positive-intrinsic-negative diode.
13. The electrostatic pen according to claim 7 wherein the first
diode is a positive-negative diode.
14. The electrostatic pen according to claim 1 wherein, the pen
point electrode, in operation, electrostatically couples to a
capacitance type sensor; and the control circuitry, in operation,
switches between the first state and the second state based on
information to be transmitted from the electrostatic pen to the
sensor.
15. The electrostatic pen according to claim 14 wherein the control
circuitry, in operation, maintains the first state when information
is not being transmitted to the sensor.
16. The electrostatic pen according to claim 14 wherein the control
circuitry, in operation, controls transmission of the information
by switching between the states, contents of the information being
associated with a transition of a transmission level.
17. An electrostatic pen, comprising: a pen point electrode;
grounding circuitry; a switch having a first terminal coupled to
the pen point electrode and having a second terminal coupled to the
grounding circuitry; and control circuitry, which, in operation,
controls transmission of information to an electronic apparatus
having a capacitive type sensor by controlling an on-off state of
the switch; and electrically couples the pen point electrode to the
grounding circuitry by setting the switch to an on state when
information is not being transmitted to the electronic
apparatus.
18. The electrostatic pen according to claim 17 wherein the control
circuitry, in operation, holds the switch in an on state for a
determined time before or after transmitting the information.
19. The electrostatic pen according to claim 17 wherein the control
circuitry, in operation, controls a switching rate of the switch to
generate an information signal of over 12 Hz.
20. The electrostatic pen according to claim 19 wherein the control
circuitry, in operation, controls the switching rate of the switch
at a frequency equal to or lower than half of a frequency
corresponding to a scanning rate of the sensor.
21. The electrostatic pen according to claim 20 wherein the control
circuitry, in operation, controls transmission of the information
by turning the switch on and off to change transmission levels of
the information signal, a direction of a transition of a
transmission level being associated with contents of the
information.
22. The electrostatic pen according to claim 21 wherein the
switching rate is 24 Hz, and half of the frequency corresponding to
the scanning rate of the sensor is 100 Hz.
23. The electrostatic pen according to claim 21 wherein the control
circuitry, in operation, controls transmission of the information
based on an association of a combination of the direction of the
transition of the transmission level and a magnitude of the
transition with the contents of the information.
24. The electrostatic pen according to claim 17 wherein the control
circuitry, in operation, controls transmission of a determined
start signal before starting transmission of the information, and
controls transmission of a determined stop signal after ending the
transmission of the information.
25. An electrostatic pen, comprising: a pen point electrode;
grounding circuitry; a switch having a first terminal coupled to
the pen point electrode and having a second terminal coupled to the
grounding circuitry; and control circuitry, which, in operation,
controls transmission of information to an electronic apparatus
including a capacitive type sensor by controlling an on-off state
of the switch to cause transitions of a transmission level, wherein
a direction of a transition of the transmission level is associated
with contents of the information.
26. A system, comprising: a capacitive sensor; and an electrostatic
pen including: a switch having: first, second and third terminals;
and a first diode having an anode coupled to the first terminal and
a cathode coupled to the third terminal; a pen point electrode
coupled to the first terminal of the switch; and control circuitry,
which, in operation: supplies respective potentials to the second
terminal and the third terminal of the switch; and switches between
two or more states including a first state in which a potential of
the second terminal is higher than a potential of the third
terminal and a second state in which the potential of the second
terminal is equal to or lower than the potential of the third
terminal.
27. The system according to claim 26 wherein the switch includes a
reverse-current limiting circuit coupled between the first terminal
and the second terminal, and, in operation, the reverse-current
limiting circuit limits a current from flowing between the first
terminal and the second terminal.
28. The system according to claim 27 wherein, the pen point
electrode, in operation, electrostatically couples to the
capacitance type sensor; and the control circuitry, in operation,
switches between the two or more states based on information to be
transmitted from the electrostatic pen to the capacitive sensor.
Description
BACKGROUND
[0001] Technical Field
[0002] The present disclosure relates to an electrostatic pen, and
particularly to a passive type electrostatic pen configured to send
information by turning on and off a switch provided between a main
body and a pen point.
[0003] Description of the Related Art
[0004] Capacitance type input systems are known which are
configured to enable an indicator such as a finger, a conductive
touch pen, or the like to indicate a position within the surface of
a touch sensor. In a capacitance type input system, the touch
sensor using a projective type mutual capacitance system is a
position detecting device configured to be able to detect the
position of an indicator. The position detecting device includes,
within a sensor surface, a plurality of X-direction electrodes each
extending in an X-direction and a plurality of Y-direction
electrodes each extending in a Y-direction. When a signal including
an alternating-current component (which signal will hereinafter be
referred to simply as a "current") is fed from an X-direction
electrode to a Y-direction electrode in a state in which the
indicator has approached the point of intersection of the
X-direction electrode and the Y-direction electrode, part of the
current that should normally flow to the Y-electrode branches and
flows to the indicator. Thus, the current detected in the
Y-direction electrode is decreased. The position detecting device
is configured to detect the position of the indicator by detecting
the change in the detected current in each of the plurality of
Y-direction electrodes.
[0005] The current flows from the position detecting device used in
the capacitance type input system to the indicator because the
indicator is grounded through a human body and a current path
occurs between the tip of the indicator and a grounding terminal.
Many of the pens now commercially available as pens for a touch
sensor (which pens are referred to as a touch pen, a stylus for the
capacitance type, a passive ES (electrostatic) pen, and the like,
and will hereinafter be referred to as "passive type electrostatic
pens") have a grounding section in contact with the human body at
some position of a casing, and thus provide the current path.
Hence, when the indicator is formed of an insulator, for example,
the current path as described above does not occur, and therefore
the position detecting device cannot detect the position of the
indicator.
[0006] Currently existing passive type electrostatic pens cannot
transmit information other than an indicated position (which
information is pen pressure, a pen type, the on-off state of a
switch, and the like) to the position detecting device unless the
passive type electrostatic pens are configured to be able to use a
separate communication channel such as Bluetooth (registered
trademark) or the like. However, a technology is known which
utilizes the above-described property and enables even a passive
type electrostatic pen to transmit information such as pen pressure
and the like to the position detecting device without a special
communication channel being prepared. This technology will be
described in detail in the following.
[0007] An electrostatic pen capable of transmitting information
includes: a main body formed of a conductor; a pen point electrode
that is a conductor insulated from the main body; a switch provided
between the pen point electrode and the main body; and a control
section that controls the on-off state of the switch according to
the transmission information. When the switch is on, the
above-described current path occurs, so that the current detected
in a Y-direction electrode is relatively decreased. When the switch
is off, on the other hand, the above-described current path does
not occur, so that the current detected in the Y-direction
electrode is relatively increased. The position detecting device
can obtain the on-off state of the switch from such a change in the
detected current, and can therefore obtain the information
transmitted by the electrostatic pen.
[0008] U.S. Patent Application Publication No. 2012/0,327,040
(hereinafter referred to as Patent Document 1) discloses an example
of an electrostatic pen capable of transmitting information. In
this electrostatic pen, a MOS (metal oxide semiconductor)
transistor is used as the above-described switch. In addition,
Patent Document 1 discloses a technology that enables
identification of the kind of a touching indicator (whether the
touching indicator is an electrostatic pen or another kind of
indicator such as a finger or the like) and identification of an
individual indicator by transmitting a signal of an arbitrary
frequency from the electrostatic pen (see paragraph [0044] and the
like) and a technology that enables transmission of information
from the electrostatic pen by transmission of a signal encoded by
using Morse code, for example (see paragraph [0043] and the
like).
BRIEF SUMMARY
[0009] However, when a MOS transistor is used as the switch for
changing a conduction state between the pen point electrode and the
main body, the accuracy of information detection in the position
detecting device is lowered. That is, the MOS transistor has a very
high stray capacitance (for example 10 pF). Thus, even after the
MOS transistor is turned off, a current flows from the position
detecting device to the electrostatic pen through this stray
capacitance. The flow of such a current reduces a difference
between the current detected in the Y-direction electrode when the
switch is on and the current detected in the Y-direction electrode
when the switch is off. As a result, the accuracy of information
detection in the position detecting device is lowered (bit error
occurrence rate is increased). Incidentally, a similar problem
occurs also when an ordinary bipolar transistor is used as the
switch. Some bipolar transistors for high frequencies have a stray
capacitance of 1 pF or less. However, the bipolar transistors for
high frequencies are susceptible to static electricity, and
therefore cannot be reliably used in practice.
[0010] An embodiment facilitates providing an electrostatic pen
that increases the accuracy of information detection in the
position detecting device.
[0011] In addition, the conventional electrostatic pens of the type
performing information transmission are designed on an assumption
that the information transmission continues to be performed at all
times. Patent Document 1 does not disclose anything about cases
where the electrostatic pen of the type performing information
transmission does not perform information transmission. In such a
situation, if the electrostatic pen of the type performing
information transmission is provided with a period in which
information transmission is not performed, and the above-described
switch is off during that period, a state in which no current path
is formed between the tip of the indicator and the grounding
terminal is continued. A problem thus occurs in position
detection.
[0012] An embodiment facilitates providing an electrostatic pen
that does not cause a problem in position detection even when the
electrostatic pen of the type performing information transmission
is provided with a period in which information transmission is not
performed.
[0013] Further, it is difficult to obtain an intermediate state
between an on state and an off state in MOS transistors and bipolar
transistors. As a result, conventional input systems cannot use
multilevel modulation for transmission of information from the
electrostatic pen.
[0014] An embodiment facilitates providing an electrostatic pen
that transmits information using multilevel modulation.
[0015] In an embodiment, an electrostatic pen includes: a switch
section having first to third terminal parts; a pen point electrode
coupled to the first terminal part; and a control section switching
between a first state in which a potential of the second terminal
part is higher than a potential of the third terminal part and a
second state in which the potential of the second terminal part is
equal to or lower than the potential of the third terminal part, by
supplying the second terminal part and the third terminal part with
the respective potentials; the switch section including a first
diode having an anode connected to the first terminal part and
having a cathode connected to the third terminal part.
[0016] In the electrostatic pen, the switch section may include a
reverse-current preventing unit disposed between the first terminal
part and the second terminal part, the reverse-current preventing
unit preventing a current from flowing from the first terminal part
to the second terminal part.
[0017] In an embodiment, in the electrostatic pen, the control
section may supply a control signal to the second terminal part and
supply an inverted signal of the control signal to the third
terminal part, and control a potential difference between the
control signal and the inverted signal to two levels or more.
[0018] In an embodiment, there is provided an electrostatic pen for
use together with an electronic apparatus including a capacitance
type sensor, the electrostatic pen including: a pen point
electrode; a grounding section; a switch section having one
terminal connected to the pen point electrode and having another
terminal connected to the grounding section; and a control section
configured to be able to transmit information to the electronic
apparatus by controlling an on-off state of the switch section;
when the control section does not transmit information to the
electronic apparatus, the control section setting the pen point
electrode and the grounding section in a state of being
electrically connected to each other by setting the switch section
in an on state.
[0019] In an embodiment, there is provided an electrostatic pen for
use together with an electronic apparatus including a capacitance
type sensor, the electrostatic pen including: a pen point
electrode; a grounding section; a switch section having one
terminal connected to the pen point electrode and having another
terminal connected to the grounding section; and a control section
configured to be able to transmit information to the electronic
apparatus by controlling an on-off state of the switch section; the
control section transmitting the information on a basis of a system
that associates a direction of a transition of a transmission
level, the transition of the transmission level being effected by
turning on or off the switch section, with contents of the
information.
[0020] According to an embodiment, the first diode passes a current
in the first state, and the first diode does not pass the current
in the second state. That is, the first diode functions as the
switch. The stray capacitance of the diode is lower than that of
MOS transistors and ordinary bipolar transistors. Hence, according
to an embodiment, the accuracy of information detection in the
position detecting device may be increased.
[0021] In an embodiment, because the reverse-current preventing
unit that prevents a current from flowing from the first terminal
part to the second terminal part is provided, the flow of the
current from the first terminal part to the second terminal part is
prevented particularly in the second state.
[0022] In an embodiment, the capacitance change in the diode due to
the potential difference at an off time is smoother than when the
MOS transistor is used as the switch. Thus, when the potential
difference between the control signal and the inverted signal is
controlled to a plurality of levels, a current flowing from the
first terminal part to the third terminal part can be controlled to
a plurality of levels. Hence, information can be transmitted using
multilevel modulation.
[0023] In an embodiment, the control section is configured to be
able to transmit information to the electronic apparatus, and the
control section sets the switch section in an on state (sets the
pen point electrode and the grounding section in a state of being
electrically connected to each other) when not transmitting
information to the electronic apparatus. Thus, even when the
electrostatic pen of the type performing information transmission
is provided with a period in which information transmission is not
performed, the touch sensor can perform position detection without
any problem. In an embodiment, the signal detected during the
period during which the transmission is not performed can also be
used as a signal in an idling time necessary to reliably detect a
start bit indicating a start of transmission of information from
the electrostatic pen. The touch sensor can therefore reliably
detect the start position of a signal corresponding to
information.
[0024] In an embodiment, the control section transmits information
on the basis of the system that associates the direction of a
transition of a signal level, the transition of the signal level
being affected by turning on or off the switch section, with
contents of the information. Thus, a time in which the position
detecting device can detect the presence of the electrostatic pen
can be mixed within a time of communication of information of one
bit irrespective of the contents of the information. Therefore
information communication can be performed while enabling position
detection without depending on the contents of the information
(deviation of binary values).
[0025] In an embodiment, an electrostatic pen comprises: a switch
having: first, second and third terminals; and a first diode having
an anode coupled to the first terminal and a cathode coupled to the
third terminal; a pen point electrode coupled to the first terminal
of the switch; and control circuitry, which, in operation: supplies
respective potentials to the second terminal and the third terminal
of the switch; and switches between two or more states including a
first state in which a potential of the second terminal is higher
than a potential of the third terminal and a second state in which
the potential of the second terminal is equal to or lower than the
potential of the third terminal. In an embodiment, the switch
includes a reverse-current limiting circuit coupled between the
first terminal and the second terminal, and, in operation, the
reverse-current limiting circuit limits a current from flowing
between the first terminal and the second terminal. In an
embodiment, the reverse-current limiting circuit comprises a
resistive element. In an embodiment, the reverse-current limiting
circuit comprises a second diode having an anode coupled to the
resistive element and having a cathode coupled to the first
terminal. In an embodiment, the control circuitry, in operation,
supplies a control signal to the second terminal. In an embodiment,
the control signal is a binary signal, which, in operation, has a
value of one of a high level and a low level. In an embodiment, the
control circuitry, in operation, supplies an inverted signal of the
control signal to the third terminal. In an embodiment, the control
circuitry, in operation, controls a potential difference between
the control signal and the inverted signal to have one of two or
more levels. In an embodiment, the control circuitry, in operation,
controls the potential difference between the control signal and
the inverted signal to have one of two or more levels in a
non-positive range of the first diode. In an embodiment, the third
terminal is coupled to a ground. In an embodiment, the
electrostatic pen comprises: a main body comprising a conductor,
the main body supporting the pen point electrode via an insulator,
wherein the third terminal is coupled to the conductor and the
conductor, in operation, is grounded through user contact with the
main body. In an embodiment, the first diode is a
positive-intrinsic-negative diode. In an embodiment, the first
diode is a positive-negative diode. In an embodiment, the pen point
electrode, in operation, electrostatically couples to a capacitance
type sensor; and the control circuitry, in operation, switches
between the first state and the second state based on information
to be transmitted from the electrostatic pen to the sensor. In an
embodiment, the control circuitry, in operation, maintains the
first state when information is not being transmitted to the
sensor. In an embodiment, the control circuitry, in operation,
controls transmission of the information by switching between the
states, contents of the information being associated with a
transition of a transmission level.
[0026] In an embodiment, an electrostatic pen comprises: a pen
point electrode; grounding circuitry; a switch having a first
terminal coupled to the pen point electrode and having a second
terminal coupled to the grounding circuitry; and control circuitry,
which, in operation, controls transmission of information to an
electronic apparatus having a capacitive type sensor by controlling
an on-off state of the switch; and electrically couples the pen
point electrode to the grounding circuitry by setting the switch to
an on state when information is not being transmitted to the
electronic apparatus. In an embodiment, the control circuitry, in
operation, holds the switch in an on state for a determined time
before or after transmitting the information. In an embodiment, the
control circuitry, in operation, controls a switching rate of the
switch to generate an information signal of over 12 Hz. In an
embodiment, the control circuitry, in operation, controls the
switching rate of the switch at a frequency equal to or lower than
half of a frequency corresponding to a scanning rate of the sensor.
In an embodiment, the control circuitry, in operation, controls
transmission of the information by turning the switch on and off to
change transmission levels of the information signal, a direction
of a transition of a transmission level being associated with
contents of the information. In an embodiment, the switching rate
is 24 Hz, and half of the frequency corresponding to the scanning
rate of the sensor is 100 Hz. In an embodiment, the control
circuitry, in operation, controls transmission of the information
based on an association of a combination of the direction of the
transition of the transmission level and a magnitude of the
transition with the contents of the information. In an embodiment,
the control circuitry, in operation, controls transmission of a
determined start signal before starting transmission of the
information, and controls transmission of a determined stop signal
after ending the transmission of the information.
[0027] In an embodiment, an electrostatic pen comprises: a pen
point electrode; grounding circuitry; a switch having a first
terminal coupled to the pen point electrode and having a second
terminal coupled to the grounding circuitry; and control circuitry,
which, in operation, controls transmission of information to an
electronic apparatus including a capacitive type sensor by
controlling an on-off state of the switch to cause transitions of a
transmission level, wherein a direction of a transition of the
transmission level is associated with contents of the
information.
[0028] In an embodiment, a system comprises: a capacitive sensor;
and an electrostatic pen including: a switch having: first, second
and third terminals; and a first diode having an anode coupled to
the first terminal and a cathode coupled to the third terminal; a
pen point electrode coupled to the first terminal of the switch;
and control circuitry, which, in operation: supplies respective
potentials to the second terminal and the third terminal of the
switch; and switches between two or more states including a first
state in which a potential of the second terminal is higher than a
potential of the third terminal and a second state in which the
potential of the second terminal is equal to or lower than the
potential of the third terminal. In an embodiment, the switch
includes a reverse-current limiting circuit coupled between the
first terminal and the second terminal, and, in operation, the
reverse-current limiting circuit limits a current from flowing
between the first terminal and the second terminal. In an
embodiment, the pen point electrode, in operation,
electrostatically couples to the capacitance type sensor; and the
control circuitry, in operation, switches between the two or more
states based on information to be transmitted from the
electrostatic pen to the capacitive sensor.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0029] FIG. 1 is a diagram showing a system configuration of a
touch type input system according to an embodiment;
[0030] FIG. 2 is a sectional view showing an example internal
configuration of an electrostatic pen shown in FIG. 1;
[0031] FIG. 3 is a diagram showing an internal configuration of an
example control section and an example switch section shown in FIG.
2;
[0032] FIG. 4A is a flowchart showing an example operation of a
transmission control circuit shown in FIG. 3, FIG. 4B is a diagram
showing an example of a signal in a case where binary modulation is
used, and FIG. 4C is a diagram showing an example of a signal in a
case where multilevel modulation is used;
[0033] FIGS. 5A and 5B are flowcharts showing example operations of
an information extraction processing section shown in FIG. 1, FIG.
5A illustrating a case where binary modulation is used, and FIG. 5B
illustrating a case where multilevel modulation is used;
[0034] FIG. 6 is a diagram showing the switch section of an
electrostatic pen according to a first embodiment;
[0035] FIGS. 7A and 7B are diagrams showing example operating
principles of the electrostatic pen shown in FIG. 6, FIG. 7A
illustrating transmission of a high level, and
[0036] FIG. 7B illustrating transmission of a low level;
[0037] FIG. 8 is a diagram showing the switch section of an
electrostatic pen according to a second embodiment;
[0038] FIGS. 9A and 9B are diagrams showing example operating
principles of the electrostatic pen shown in FIG. 8, FIG. 9A
illustrating transmission of a high level, and
[0039] FIG. 9B illustrating transmission of a low level;
[0040] FIG. 10 is a diagram showing the switch section of an
electrostatic pen according to a third embodiment;
[0041] FIGS. 11A and 11B are diagrams showing example operating
principles of the electrostatic pen shown in FIG. 10, FIG. 11A
illustrating transmission of a high level, and FIG. 11B
illustrating transmission of a low level; and
[0042] FIG. 12 is a diagram showing the reverse
voltage-interterminal capacitance characteristic of an ordinary
diode.
DETAILED DESCRIPTION
[0043] Example embodiments will hereinafter be described in detail
with reference to the accompanying drawings. In the present
specification, three embodiments are cited to describe touch type
input systems according to embodiments. Description will first be
made of parts common to the three embodiments, and thereafter
description will be made of each of the three embodiments.
[0044] First, with regard to the parts common to the three
embodiments, as shown in FIG. 1, a touch type input system 1
according to an embodiment includes an electrostatic pen 2 and a
touch sensor 3.
[0045] The electrostatic pen 2 is an indicator for a human to
indicate a position on the touch sensor 3. The electrostatic pen 2
includes: a main body 20 (grounding section) formed of a
cylindrical conductor; a pen point tip 21, which is an insulator or
a dielectric; a pen point electrode 24 housed within the pen point
tip 21; and a switch section 27 to control a conduction state
between the pen point electrode 24 and the main body 20. The
electrostatic pen 2 is generally used in a state in which a hand 4
illustrated in FIG. 1 holds the main body 20. Therefore the main
body 20 is usually grounded through a human body, as shown in FIG.
1.
[0046] The touch sensor 3 is for example a position detecting
device (electronic apparatus) having a flat sensor, such as a
digitizer, a tablet PC (personal computer), or the like. The touch
sensor 3 is configured to detect a position indicated by the
electrostatic pen 2 on the sensor by a cross-point type mutual
capacitance system as a kind of projective type capacitance system.
Specifically, the sensor of the touch sensor 3 has a configuration
formed by arranging m X-direction electrodes 35 (X-direction
electrodes 35-1 to 35-m) each extending in an X-direction at equal
intervals and n Y-direction electrodes 36 (Y-direction electrodes
36-1 to 36-n) each extending in a Y-direction (direction orthogonal
to the X-direction within the surface of the sensor) at equal
intervals.
[0047] As shown in FIG. 1, the touch sensor 3 includes, in addition
to the sensor, circuitry including a transmission signal processing
section 30, a received signal processing section 31, a control
section 32, and an information extraction processing section
33.
[0048] The transmission signal processing section 30 has a function
of sequentially outputting a determined alternating-current signal
to the m X-direction electrodes 35. Timing in which the
transmission signal processing section 30 outputs the signal is
controlled by the control section 32. The alternating-current
signal supplied to an X-direction electrode 35 by the transmission
signal processing section 30 is supplied to each Y-direction
electrode 36 through a capacitance occurring between the
X-direction electrode 35 and each Y-direction electrode 36
vertically opposed to the X-direction electrode 35. The received
signal processing section 31 has an analog-to-digital converter to
receive the alternating-current signal that has thus arrived at
each Y-direction electrode 36. The received signal processing
section 31 digitizes the value (level) of the received signal from
each Y-direction electrode 36 by the analog-to-digital converter,
and outputs the signal value to the control section 32. The control
section 32 detects the position of the electrostatic pen 2 on the
touch sensor 3 from the thus supplied signal value and supplies the
supplied signal value to the information extraction processing
section 33. The information extraction processing section 33 has a
function of receiving information transmitted by the electrostatic
pen 2 on the basis of the signal value supplied from the control
section 32.
[0049] Description will be made of detection of the position of the
electrostatic pen 2. First, at a point of intersection of an
X-direction electrode 35-k (k is an integer of 1 to m) and a
Y-direction electrode 36-j (j is an integer of 1 to n) (see, e.g.,
FIGS. 7A, 7B, 9A, 9B, 11A and 11B), for example, there is a
capacitance obtained by combining capacitances C1 and C2 shown in
FIG. 1 with each other when the pen point tip 21 of the
electrostatic pen 2 is not present. In this case, when the pen
point tip 21 of the electrostatic pen 2 approaches this point of
intersection, a capacitance D shown in FIG. 1 is generated. The
capacitance D guides part of a current that would be supplied
through the capacitance obtained by combining the capacitances C1
and C2 with each other when the pen point tip 21 is not present.
When the pen point tip 21 of the electrostatic pen 2 approaches and
thus the capacitance D becomes large with respect to the
capacitance C2, part of the current sent out from the X-direction
electrode 35-k flows out to a grounding terminal through a current
path P2 formed in the electrostatic pen 2 and the hand 4 (in a case
where the switch section 27 is on (a case where the switch section
27 is off will be described later)). As a result, the current
detected by the received signal processing section 31 in relation
to the Y-direction electrode 36-j is decreased. Thus, the signal
value supplied from the received signal processing section 31 to
the control section 32 in relation to the Y-direction electrode
36-j is decreased. The control section 32 detects that the pen
point tip 21 of the electrostatic pen 2 is in proximity to the
point of intersection of the X-direction electrode 35-k and the
Y-direction electrode 36-j on the basis of such a change in the
signal value.
[0050] Description will next be made of reception of information
transmitted by the electrostatic pen 2. As will be described later
in detail, the electrostatic pen 2 controls the on-off state of the
switch section 27 according to the information to be transmitted.
When the switch section 27 is in an on state, the pen point
electrode 24 and the hand 4 are electrically connected to each
other, so that the above-described current path P2 is formed
between the pen point electrode 24 and the grounding terminal.
Hence, in this case, when the pen point tip 21 of the electrostatic
pen 2 approaches the point of intersection of the X-direction
electrode 35 and the Y-direction electrode 36, the signal value
supplied from the received signal processing section 31 to the
control section 32 in relation to the point of intersection is
decreased, as described above. When the switch section 27 is in an
off state, on the other hand, the pen point electrode 24 is
electrically disconnected from the grounding terminal, and is thus
set in a floating state, so that the above-described current path
P2 is not formed. Hence, in this case, even when the pen point tip
21 of the electrostatic pen 2 approaches the point of intersection
of the X-direction electrode 35 and the Y-direction electrode 36,
the signal value supplied from the received signal processing
section 31 to the control section 32 in relation to the point of
intersection is not decreased as described above.
[0051] In this case, the on-off control of the switch section 27 by
the electrostatic pen 2 is performed using a frequency at which the
signal detected on the side of the position detecting device can be
identified as not being a signal resulting from a human operating
the electrostatic pen 2. For example, the switch section 27 is
subjected to on-off control at a rate such that the communicated
signal has a frequency over 12 Hz.
[0052] Here, the numerical value exceeding 12 Hz is a value
determined on the basis of a knowledge that even when a human
operates the electrostatic pen 2 upward and downward (in a vertical
direction) with respect to the sensor at high speed, the number of
times that the electrostatic pen 2 is detected on the position
detecting device side does not exceed 12 per second. Incidentally,
when information is encoded by a Manchester code and then
transmitted, as will be described later, depending on a row of 0s
and 1s, the frequency of the signal may be half the on-off
frequency of the switch. Thus, the switch is turned on and off at a
rate exceeding 24 Hz.
[0053] Hence, when changes in signal value as described above are
construed as a binary signal constituted of two values, that is, a
large signal value and a small signal value, the information
transmitted by the electrostatic pen 2 is superimposed on a
frequency component exceeding 12 Hz in the binary signal. The
information extraction processing section 33 accordingly extracts
the frequency component exceeding 12 Hz from the signal represented
by the changes in the signal value supplied from the control
section 32, and demodulates the information transmitted by the
electrostatic pen 2 on the basis of the extracted frequency
component.
[0054] In an embodiment, the rate of on-off control of the switch
section 27 by the electrostatic pen 2 is set to a frequency equal
to or lower than half a frequency corresponding to the scanning
rate of the touch sensor 3. For example, when the touch sensor 3 in
which the scanning rate of the sensor is 200 Hz is used, the
frequency of on-off control of the switch section 27 by the
electrostatic pen 2 may be 100 Hz or lower. This controls the
frequency of the signal to 100 Hz or lower even in the case of any
row of binary values. Thus, the reception of the information in the
touch sensor 3 can be performed with the scanning rate of 200 Hz
set as a sampling frequency.
[0055] A configuration of the electrostatic pen 2 will be described
in more detail with reference to FIG. 2 and FIG. 3. As shown in
FIG. 2, the electrostatic pen 2 includes, in addition to the main
body 20, the pen point tip 21, and the pen point electrode 24
described above, an insulating section 22 and a substrate 23.
Various kinds of circuits are formed on the substrate 23. The
circuits comprise a power supply section 25, a control section 26,
and the switch section 27.
[0056] The main body 20 comprises a conductor, as described above.
On the other hand, the pen point tip 21 and the insulating section
22 comprise an insulator. The main body 20 supports the pen point
electrode 24 via these insulators. The main body 20 and the pen
point electrode 24 are therefore insulated from each other. In
addition, the substrate 23 is electrically coupled to the main body
20, and is grounded through the main body 20 and a human body (hand
4) touching the main body 20.
[0057] The power supply section 25 is a power supply to supply
power necessary for the operation of the control section 26 and the
switch section 27. Specifically, a battery is for example suitably
used as the power supply section 25.
[0058] The control section 26 is a functional unit that generates
information to be transmitted to the touch sensor 3, and which
controls the switch section 27 on the basis of the generated
information. As shown in FIG. 3, the control section 26 includes a
transmission data generating circuit 26a, a transmission control
circuit 26b, and a switch control signal output circuit 26c.
[0059] The transmission data generating circuit 26a obtains
information to be transmitted to the touch sensor 3, and assembles
transmission information on the basis of the obtained information.
The information obtained by the transmission data generating
circuit 26a can include information indicating a pen pressure
detected by a pen pressure detecting mechanism (not shown) within
the electrostatic pen 2, information indicating the on-off state of
a side switch (not shown) provided to the side surface of the
electrostatic pen 2, and the like. However, the information
obtained by the transmission data generating circuit 26a is not
limited to these pieces of information.
[0060] The transmission control circuit 26b performs on-off control
of the switch section 27 on the basis of the transmission
information generated by the transmission data generating circuit
26a. Specifically, the transmission control circuit 26b determines
a transmission level on the basis of the transmission information,
and sends out data indicating the determined transmission level to
the switch control signal output circuit 26c.
[0061] Examples of the control of the transmission level by the
transmission control circuit 26b will be described in detail with
reference to FIGS. 4A and 4B. As shown in FIG. 4A, the transmission
control circuit 26b first determines whether or not an information
transmission period has arrived (step S1). When determining that
the information transmission period has not arrived, the
transmission control circuit 26b sets the transmission level to an
"ON" state, as shown in FIG. 4B. The switch section 27 is thereby
maintained in the on state (step S2). Therefore a state in which
the pen point electrode 24 and the main body 20 are electrically
connected to each other is maintained. The touch sensor 3 according
to the present embodiment can thus detect the position of the
electrostatic pen 2 without any problem even outside the
information transmission period.
[0062] When determining that the information transmission period
has arrived in step S1, on the other hand, the transmission control
circuit 26b controls the transmission level on the basis of the
transmission information generated by the transmission data
generating circuit 26a (step S3). More specifically, the
transmission control circuit 26b first controls the transmission
level so as to indicate a determined start signal, and next
controls the transmission level on the basis of the transmission
information in bit units. After ending the control for all of bits
constituting the transmission information, the transmission control
circuit 26b controls the transmission level so as to indicate a
determined stop signal.
[0063] The control of the transmission level on the basis of the
transmission information in bit units may be performed specifically
by a system that associates transitions of the transmission level
with the contents of the information, that is, a so-called
Manchester system. In the present embodiment, the transmission
control circuit 26b associates only directions of transitions of
the transmission level with the contents of the information. More
specifically, as shown in FIG. 4B, a fall in the transmission level
(transition from "ON" to "OFF") is associated with transmission
information "0," and a rise in the transmission level (transition
from "OFF" to "ON") is associated with transmission information
"1." An opposite association may also be employed, of course.
[0064] As shown in FIG. 4B, the start signal and the stop signal
are both transmitted using a transmission time for one chip of the
Manchester code. In the present embodiment, the transmission
control circuit 26b controls the transmission level in a similar
manner to the transmission information "1" for the start signal,
and controls the transmission level so as to fix the transmission
level to "ON" for the stop signal.
[0065] An example of the processing of received signals in the
information extraction processing section 33 shown in FIG. 1 will
be described in the following with reference to FIG. 5A. As
described above, the information extraction processing section 33
is sequentially supplied with signal values of received signals
from the control section 32. The information extraction processing
section 33 monitors the series of signal values thus supplied, and
detects the above-described start signal (step S10). Specifically,
when the transmission level of the signal values rises by a
determined level or more after being at a certain level for a
determined time, it is determined that the start signal is
detected.
[0066] After detecting the start signal, the information extraction
processing section 33 next receives data (step S11). In the present
embodiment, as described above, transmission is made by the
Manchester system. The information extraction processing section 33
accordingly detects variations (rise or fall) in the transmission
level by sequentially making binary threshold value determination
for the series of signal values supplied from the control section
32. The information extraction processing section 33 thereby
receives data transmitted by the electrostatic pen 2 (transmission
information generated by the transmission data generating circuit
26a).
[0067] The information extraction processing section 33 repeats
detection of the above-described stop signal while receiving the
data (step S12). Specifically, when a determined time has passed
with the transmission level of the series of signal values supplied
from the control section 32 remaining in the "ON" state, it is
determined that the stop signal is detected. When the stop signal
is detected, the information extraction processing section 33
determines that the information transmission period is ended. The
information extraction processing section 33 then returns to step
S10 to start the operation of detecting the start signal.
Incidentally, it is not essential to use such a stop signal in
communication between the electrostatic pen 2 and the touch sensor
3. However, the use of the stop signal facilitates making the
information extraction processing section 33 recognize an end of
the information transmission period even when the bit length of the
information transmission period is not fixed. Hence, information
having an arbitrary amount of information can be transmitted from
the electrostatic pen 2 to the touch sensor 3.
[0068] Thus, the signal (information) detected during the period
during which information transmission is not made, which signal
(information) is maintained in an "ON" state, can be not only used
for position detection by the position detecting device but also
used as a signal in an idling time necessary to detect the start
bit indicating a start of transmission of information from the
electrostatic pen and the stop bit.
[0069] The description returns to FIG. 3. The switch control signal
output circuit 26c outputs a signal for performing on-off control
of the switch section 27 on the basis of the data supplied from the
transmission control circuit 26b. Specifically, the switch control
signal output circuit 26c generates a control signal Vsig that is
set to a high level in correspondence with a transmission level
"ON" and which is set to a low level in correspondence with a
transmission level "OFF," and supplies the control signal Vsig to
the switch section 27. The switch control signal output circuit 26c
also has a function of supplying the switch section 27 with an
inverted signal/Vsig of the control signal Vsig or a ground
potential GND (low-level potential). Incidentally, in a first
embodiment (FIG. 6 and FIGS. 7A and 7B) and a second embodiment
(FIG. 8 and FIGS. 9A and 9B) to be described later, description
will be made of an example in which the control signal Vsig and the
ground potential GND are supplied from the switch control signal
output circuit 26c to the switch section 27. In a third embodiment
(FIG. 10 and FIGS. 11A and 11B) to be described later, on the other
hand, description will be made of an example in which the control
signal Vsig and the inverted signal/Vsig are supplied from the
switch control signal output circuit 26c to the switch section
27.
[0070] As shown in FIG. 3, the switch section 27 includes: a first
terminal part E1 coupled to the pen point electrode 24; a second
terminal part E2 supplied with the control signal Vsig from the
switch control signal output circuit 26c; a third terminal part E3
supplied with the inverted signal/Vsig or the ground potential GND
from the switch control signal output circuit 26c; a first diode
27a having an anode coupled to the first terminal part E1 and
having a cathode coupled to the third terminal part E3; and a
reverse-current preventing or limiting circuit/unit 27b coupled
between the first terminal part E1 and the second terminal part
E2.
[0071] When the control signal Vsig supplied from the switch
control signal output circuit 26c is at a high level, the switch
section 27 assumes a state (first state) in which the potential of
the second terminal part E2 is higher than the potential of the
third terminal part E3. In this case, the first diode 27a is in an
on state, so that a current can be made to flow from the first
terminal part E1 to the third terminal part E3. That is, the switch
section 27 is in an on state, and the current path P2 shown in FIG.
1 is formed. When the control signal Vsig supplied from the switch
control signal output circuit 26c is at a low level, on the other
hand, the switch section 27 assumes a state (second state) in which
the potential of the second terminal part E2 is equal to or lower
than the potential of the third terminal part E3. In this case, the
first diode 27a is in an off state, so that no current flows from
the first terminal part E1 to the third terminal part E3. That is,
the switch section 27 is in an off state, and the current path P2
shown in FIG. 1 is blocked.
[0072] The electrostatic pen 2 thus controls the on-off state of
the switch section 27 by the potential level of the control signal
Vsig supplied to the switch section 27 by the switch control signal
output circuit 26c. It is the first diode 27a, and not a switching
element such as a MOS transistor, a bipolar transistor, or the
like, that functions as an entity of a switch within the switch
section 27. A diode has a lower stray capacitance than a MOS
transistor or an ordinary bipolar transistor. The first diode 27a
can therefore block the current path P2 more reliably after the
control signal Vsig is changed from a high level to a low level.
Hence, the electrostatic pen 2 can increase the accuracy of
information detection in the touch sensor 3.
[0073] Incidentally, while a PN (positive-negative) diode, which is
a most basic diode, can be used as the first diode 27a, in an
embodiment a PIN (p-intrinsic-n) diode, which comprises a
semiconductor layer having a high electric resistance interposed
between a P-region and an N-region, may be used. The PIN diode has
a characteristic of a low capacitance between terminals (junction
capacitance between the P-region and the N-region) because the PIN
diode has the semiconductor layer having a high electric resistance
between the P-region and the N-region. Due to this characteristic,
the PIN diode has a stray capacitance even lower than the PN diode.
To cite concrete numerical values, in a PIN diode the stray
capacitance in a state in which a potential difference between the
P-region and the N-region is zero is typically about 0.5 pF, and
the stray capacitance is typically about 0.8 pF at a maximum.
Hence, the use of a PIN diode as the first diode 27a facilitates
realizing a low stray capacitance of 1 pF or less. Thus, a current
flowing in from the first terminal part E1 can be blocked even more
reliably after the control signal Vsig is changed from a high level
to a low level. The accuracy of information detection in the touch
sensor 3 can therefore be further increased.
[0074] The reverse-current preventing unit 27b prevents a current
from flowing from the first terminal part E1 to the second terminal
part E2 particularly when the second terminal part E2 has a low
potential level. For example, a resistive element or a diode can be
used as the reverse-current preventing unit 27b. This will be
separately described in detail in the first to third embodiments to
be described later.
[0075] The above description has been made of the parts common to
the three embodiments in the touch type input system 1 according to
the present embodiment. Next, the three embodiments will each be
described sequentially. Differences in the three embodiments are
differences in configuration of the switch control signal output
circuit 26c and the switch section 27. Thus, description in the
following will be made directing attention to these
differences.
[0076] As shown in FIG. 6, the switch section 27 according to the
first embodiment includes a resistive element 27ba as the
reverse-current preventing unit 27b. In addition, the third
terminal part E3 is supplied with the ground potential GND from the
switch control signal output circuit 26c. Incidentally, the ground
potential GND supplied to the switch control signal output circuit
26c is supplied to the substrate 23 through the main body 20 and
the hand 4 (see FIG. 2).
[0077] The resistive element 27ba has a role of suppressing a
current (reverse-current) flowing from the first terminal part E1
to the second terminal part E2. The resistance value of the
resistive element 27ba therefore needs to be large enough to be
able to suppress the current sufficiently. On the other hand, the
resistance value of the resistive element 27ba cannot be made too
large because too large a resistance value of the resistive element
27ba slows on-off switching response of the switch section 27. To
cite concrete numerical values, in the present embodiment, the
resistive element 27ba may need to have 100 k.OMEGA. or more to
prevent the reverse-current, and the resistive element 27ba may
need to have 10 M.OMEGA. or less in consideration of the switching
response. Hence, in the present embodiment, the resistance value of
the resistive element 27ba may be 100 k.OMEGA. to 10 M.OMEGA., and
in an embodiment may be set to about 3 M.OMEGA..
[0078] Operation of the switch section 27 according to the present
embodiment will be described with reference to FIGS. 7A and 7B.
Incidentally, the following description supposes that a determined
signal is transmitted from the transmission signal processing
section 30 to the received signal processing section 31 within the
touch sensor 3 shown in FIG. 1 through a current path P1 shown in
FIGS. 7A and 7B (path from the transmission signal processing
section 30 through the X-direction electrode 35-k and the
Y-direction electrode 36-j to the received signal processing
section 31), and supposes that the pen point electrode 24 of the
electrostatic pen 2 held by a person is in proximity to the point
of intersection of the X-direction electrode 35-k and the
Y-direction electrode 36-j.
[0079] When the control signal Vsig is at a high level, the first
diode 27a is in an on state, as shown in FIG. 7A. As a result, the
current path P2 is formed between the pen point electrode 24 and
the grounding terminal. The current path P2 is coupled to the
current path P1 via the capacitance D formed between the pen point
electrode 24 and the sensor surface of the touch sensor 3. Part of
the current flowing from the transmission signal processing section
30 to the received signal processing section 31 therefore flows out
to the grounding terminal via the current path P2. Consequently,
the signal value detected by the analog-to-digital converter within
the received signal processing section 31 is relatively decreased,
and the information extraction processing section 33 shown in FIG.
1 obtains a value "ON" of a received signal Sig from this
decrease.
[0080] When the control signal Vsig is at a low level,
alternatively, the first diode 27a is in an off state, as shown in
FIG. 7B. As a result, the current path P2 from the first terminal
part E1 to the third terminal part E3 as in the case of FIG. 7A is
not formed. Therefore all of the current flowing from the
transmission signal processing section 30 to the received signal
processing section 31 flows into the received signal processing
section 31. Consequently, the signal value detected by the
analog-to-digital converter within the received signal processing
section 31 is relatively increased, and the information extraction
processing section 33 shown in FIG. 1 obtains a value "OFF" of the
received signal Sig from this increase.
[0081] Here, consideration will be given to the current path P2
from the first terminal part E1 to the second terminal part E2. If
a current flows through this current path P2, the current flowing
into the received signal processing section 31 is correspondingly
decreased. However, in the present embodiment, the resistive
element 27ba having a large resistance value is provided between
the first terminal part E1 and the second terminal part E2. A
current therefore hardly flows through the path branching in a
direction from the first terminal part E1 to the second terminal
part E2. Hence, when the first diode 27a is set in an off state, it
is possible to prevent the current flowing into the received signal
processing section 31 from being decreased and thus prevent the
value of Sig from being erroneously detected as the value "ON."
[0082] As described above, according to the input system 1
according to the present embodiment, the switch control signal
output circuit 26c controls the potential level of the control
signal Vsig according to transmission information, whereby the
information extraction processing section 33 can be made to receive
the transmission information. Then, the first diode 27a, which is a
diode having a low stray capacitance, functions as the entity of a
switch within the switch section 27. Thus, the current path P2 can
be blocked reliably after the control signal Vsig is changed from a
high level to a low level. Hence, the accuracy of information
detection in the touch sensor 3 can be increased.
[0083] In addition, the resistive element 27ba is provided as the
reverse-current preventing unit 27b. Thus, particularly when the
control signal Vsig is at a low level, it is possible to prevent a
current from flowing from the first terminal part E1 to the second
terminal part E2 (flowing backward).
[0084] Next, as shown in FIG. 8, an input system 1 according to the
second embodiment is different from the input system 1 according to
the first embodiment in that the reverse-current preventing unit
27b is formed by a resistive element 27ba and a second diode 27bb
connected in series with each other. The input system 1 according
to the second embodiment is otherwise similar to the input system 1
according to the first embodiment. The present embodiment
facilitates realizing, with the addition of the second diode 27bb,
a reduction in the resistance value of the resistive element 27ba
as compared with the first embodiment, and thereby facilitates
realizing an increase in speed of on-off switching response of the
switch section 27. Description in the following will be made
directing attention to differences from the input system 1
according to the first embodiment.
[0085] The resistive element 27ba and the second diode 27bb are
coupled in series with each other between the second terminal part
E2 and the first terminal part E1 in this order. That is, one
terminal of the resistive element 27ba is coupled to the second
terminal part E2. Another terminal of the resistive element 27ba
and an anode of the second diode 27bb are coupled to each other. A
cathode of the second diode 27bb is coupled to the first terminal
part E1.
[0086] As described in the first embodiment, the resistance value
of the resistive element 27ba needs to be large enough to be able
to suppress a current sufficiently, whereas too large a resistance
value of the resistive element 27ba slows the on-off switching
response of the switch section 27. That is, the speed of the
switching response and the reverse-current preventing effect are in
a trade-off relation. According to the present embodiment, the
second diode 27bb whose cathode is coupled to the first terminal
part E1 is provided in series with the resistive element 27ba.
Thus, on condition that the second diode 27bb be off, the second
diode 27bb plays a role of preventing a current from flowing from
the first terminal part E1 to the second terminal part E2. Hence,
even when the resistive element 27ba has a small resistance value,
a sufficient reverse-current preventing effect can be obtained, so
that an increase in speed of the switching response can be
achieved.
[0087] Operation of the switch section 27 according to the present
embodiment will be described with reference to FIGS. 9A and 9B. A
presupposition in FIGS. 9A and 9B is similar to that of FIGS. 7A
and 7B.
[0088] When the control signal Vsig is at a high level, as shown in
FIG. 9A, the first diode 27a and the second diode 27bb are both in
an on state. As a result, the current path P2 is formed between the
pen point electrode 24 and the grounding terminal. The effect
produced by the formation of the current path P2 is similar to that
of the first embodiment described with reference to FIGS. 7A and
7B. Incidentally, in this case, the second diode 27bb is on. Thus,
as shown in FIG. 9A, a current also flows from the first terminal
part E1 to the second terminal part E2. However, even when this
current flows, the signal value detected by the analog-to-digital
converter within the received signal processing section 31 is
decreased all the same.
[0089] When the control signal Vsig is at a low level, on the other
hand, as shown in FIG. 9B, the first diode 27a and the second diode
27bb are both in an off state. As a result, the current path P2 as
in the case of FIG. 9A is not formed, of course, and the current
path connecting the first terminal part E1 and the second terminal
part E2 to each other is not formed either. This prevents part of
the current flowing into the received signal processing section 31
from flowing (leaking) into the electrostatic pen 2. The
information extraction processing section 33 shown in FIG. 1 can
therefore obtain the value "OFF" of the received signal Sig more
reliably.
[0090] As described above, according to the input system 1
according to the present embodiment, in addition to effects similar
to those of the first embodiment, it is possible to obtain a
further effect of more reliably preventing a current from flowing
from the first terminal part E1 to the second terminal part E2
(flowing backward) when the control signal Vsig is at a low level.
In addition, because the second diode 27bb is provided, the
resistance value of the resistive element 27ba can be reduced (for
example set to 1 k.OMEGA. to 100 k.OMEGA.). Thus, the on-off
switching response of the switch section 27 can be increased in
speed as compared with the first embodiment.
[0091] Incidentally, as in the case of the first diode 27a, while a
PN diode, which is a most basic diode, can be used as the second
diode 27bb, a PIN diode described above in an embodiment is used as
the second diode 27bb. This can more reliably block the current
flowing in from the first terminal part E1 to the electrostatic pen
2 after the control signal Vsig is changed from a high level to a
low level.
[0092] Next, as shown in FIG. 10, an input system 1 according to
the third embodiment is different from the input system 1 according
to the second embodiment in that the inverted signal/Vsig of the
control signal Vsig is supplied from the switch control signal
output circuit 26c to the third terminal part E3. The input system
1 according to the third embodiment is otherwise similar to the
input system 1 according to the second embodiment. Description in
the following will be made directing attention to differences from
the input system 1 according to the second embodiment.
[0093] Because the third terminal part E3 is supplied with the
inverted signal/Vsig, as shown in FIG. 11B, the first diode 27a and
the second diode 27bb when the control signal Vsig is at a low
level are in a reverse-biased state in which the respective
cathodes of the first diode 27a and the second diode 27bb have
potentials higher than the respective anodes of the first diode 27a
and the second diode 27bb. As indicated by a characteristic curve A
in FIG. 12, a diode generally has a property such that the higher
the reverse voltage, the lower the interterminal capacitance of the
diode. Because of this property, the interterminal capacitance of
the diode in the reverse-biased state as described above is usually
lower than in the case where the potential of the cathode and the
potential of the anode are the same. Hence, the input system 1
according to the present embodiment can more reliably block a
current flowing in from the first terminal part E1 to the
electrostatic pen 2 than the second embodiment. It can also be said
from another point of view that the input system 1 according to the
present embodiment can block the current flowing in from the first
terminal part E1 to the electrostatic pen 2 more reliably even when
a PN diode rather than a PIN diode is used as the first diode 27a
and the second diode 27bb.
[0094] The input system 1 according to the present embodiment has
another effect of being able to use multilevel modulation for
transmitting information from the electrostatic pen 2 to the touch
sensor 3. A case where multilevel modulation is used will be
described in detail in the following as a modification of the
present embodiment.
[0095] The input system 1 according to the present modification
realizes multilevel modulation by controlling the potential level
of the control signal Vsig to two levels or more in a range in
which a voltage across the first diode 27a is not a
positive-direction voltage (non-positive range). For example,
supposing that the potential level of the control signal Vsig is
controlled to two levels of 1 V and 2 V, potential differences of
four levels, that is, +2-(-2)=4 V, +1-(-1)=2 V, -1-(+1)=-2 V,
-2-(+2)=-4 V can be applied between the second terminal part E2 and
the third terminal part E3. Of the potential differences, -2 V and
-4 V are potential differences within the non-positive range of the
first diode 27a. The switch control signal output circuit 26c
according to the present modification realizes multilevel
modulation by using -2 V and -4 V falling within the non-positive
range and at least one of the potential differences not falling
within the non-positive range (4 V or 2 V in this case).
[0096] Referring to the characteristic curve A in FIG. 12 again,
the interterminal capacitance of a diode has a property of
monotonically decreasing with respect to the reverse voltage.
Hence, stepwise control of the reverse voltage applied to the first
diode 27a as described above can affect stepwise control of the
current flowing from the first terminal part E1 into the
electrostatic pen 2 after the control signal Vsig is changed to a
low level. Utilizing this, the transmission control circuit 26b
according to the present modification (see FIG. 10) controls the
transmission level of data to a plurality of levels, thereby
realizing data modulation by multilevel modulation. A procedure for
data transmission and reception in the present modification will be
concretely described in the following with reference to FIG. 4C and
FIG. 5B.
[0097] As shown in FIG. 4C, the transmission control circuit 26b
according to the present modification uses three levels "ON,"
"OFF2," and "OFF1" as the transmission levels of data. The
transmission level "ON" corresponds to a state in which the switch
section 27 is on. On the other hand, while the transmission levels
"OFF2" and "OFF1" both correspond to a state in which the switch
section 27 is off, voltages applied across the first diode 27a at
the respective transmission levels are different from each other.
In FIG. 4C, the reverse voltage applied across the first diode 27a
is increased in order of the transmission levels "OFF2" and
"OFF1."
[0098] Then, the transmission control circuit 26b according to the
present modification controls the transmission level on the basis
of a system that associates the contents of transmission
information with combinations of directions of transitions of the
transmission level and magnitudes of the transitions. Specifically,
as shown in FIG. 4C, a fall from the transmission level "ON" to
"OFF1" is associated with transmission information "00," a fall
from the transmission level "ON" to "OFF2" is associated with
transmission information "01," a rise from the transmission level
"OFF1" to "ON" is associated with transmission information "10,"
and a rise from the transmission level "OFF2" to "ON" is associated
with transmission information "11." As for a start signal and a
stop signal, as shown in FIG. 4C, control of the transmission level
in a similar manner to the transmission information "10" is
performed for the start signal, and control is performed so as to
fix the transmission level to "ON" for the stop signal. Data
transmission by multilevel modulation is thus realized.
Incidentally, in the above-described transmission level control, a
rise from the transmission level "OFF1" to "OFF2" and a fall from
the transmission level "OFF2" to "OFF1" are not associated with
transmission information. However, the rise from the transmission
level "OFF1" to "OFF2" and the fall from the transmission level
"OFF2" to "OFF1" may of course be associated with transmission
information as long as no problem occurs in position detection.
[0099] The information extraction processing section 33 (see FIG.
1) as a receiving side receiving data thus transmitted by using
multilevel modulation receives the data using also the intermediate
level, as shown in FIG. 5B. That is, the information extraction
processing section 33 according to the above-described embodiment
receives data transmitted by the electrostatic pen 2 by
sequentially making binary threshold value determination for a
series of signal values supplied from the control section 32. On
the other hand, the information extraction processing section 33
according to the present modification receives data transmitted by
the electrostatic pen 2 by sequentially making multilevel (three
values in the example of FIG. 4C) threshold value determination for
a series of signal values supplied from the control section 32
(step S13). The reception of data transmitted by multilevel
modulation is thereby realized.
[0100] As described above, the input system 1 according to the
present modification can control the current flowing from the first
terminal part E1 to the third terminal part E3 to a plurality of
levels through the control of the potential difference between the
control signal Vsig and the inverted signal/Vsig to a plurality of
levels. Thus, multilevel modulation can be used for transmission of
information from the electrostatic pen 2 to the touch sensor 3.
Hence, more information can be transmitted than in the case where
binary modulation is used.
[0101] Example embodiments have been described above. However, the
present disclosure is not at all limited to such embodiments. The
present disclosure can of course be carried out in various modes
without departing from the spirit of the present disclosure.
[0102] For example, in the foregoing embodiments, description has
been made of cases where an electrostatic pen is used together with
a touch sensor of a cross-point type mutual capacitance system.
However, an electrostatic pen according to the present disclosure
is applicable together with various types of sensors of a
capacitance system that detects a change in capacitance. For
example, an electrostatic pen according to the present disclosure
is applicable together with sensors of a surface type capacitance
system and other types of sensors of the projective type
capacitance system (self-capacitance type and the like).
* * * * *