U.S. patent application number 12/986849 was filed with the patent office on 2012-06-14 for position indicator.
This patent application is currently assigned to Wacom Co., Ltd.. Invention is credited to Yasuo Oda, Masaki Yagi.
Application Number | 20120146958 12/986849 |
Document ID | / |
Family ID | 44050156 |
Filed Date | 2012-06-14 |
United States Patent
Application |
20120146958 |
Kind Code |
A1 |
Oda; Yasuo ; et al. |
June 14, 2012 |
POSITION INDICATOR
Abstract
A position indicator is provided for use with a position
detecting sensor that carries out position detection by detecting a
change in capacitance. The position indicator includes: a first
electrode configured to receive an alternating-current (AC) signal
from the position detecting sensor; a signal enhancing processing
circuit configured to subject the AC signal received via the first
electrode to determined signal enhancing processing; and a second
electrode different from the first electrode and configured to be
supplied with a signal output from the signal enhancing processing
circuit. An enhanced signal having a determined correlation with
the AC signal received via the first electrode from the position
detecting sensor is formed while the enhanced signal is sent out to
the position detecting sensor via the second electrode.
Inventors: |
Oda; Yasuo; (Saitama,
JP) ; Yagi; Masaki; (Saitama, JP) |
Assignee: |
Wacom Co., Ltd.
Saitama
JP
|
Family ID: |
44050156 |
Appl. No.: |
12/986849 |
Filed: |
January 7, 2011 |
Current U.S.
Class: |
345/179 ;
178/19.03 |
Current CPC
Class: |
G06F 3/03545 20130101;
G06F 3/0441 20190501; G06F 3/0442 20190501; G06F 3/046 20130101;
G06F 3/0446 20190501 |
Class at
Publication: |
345/179 ;
178/19.03 |
International
Class: |
G06F 3/044 20060101
G06F003/044 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 14, 2010 |
JP |
2010-278002 |
Claims
1. A position indicator for use in conjunction with a position
detecting sensor that carries out position detection by detecting a
change in capacitance, the position indicator comprising: a first
electrode configured to receive an alternating-current (AC) signal
from the position detecting sensor; a signal enhancing processing
circuit configured to subject the AC signal received via the first
electrode to determined signal enhancing processing; and a second
electrode different from the first electrode and configured to be
supplied with an enhanced signal output from the signal enhancing
processing circuit; wherein the first electrode and the second
electrode are both disposed at the same end section of the position
indicator, wherein the enhanced signal having a determined
correlation with the AC signal received via the first electrode
from the position detecting sensor is formed while the enhanced
signal is sent out to the position detecting sensor via the second
electrode, and wherein the signal enhancing processing circuit
generates the enhanced signal having a signal level higher than a
signal level of the AC signal received via the first electrode.
2. (canceled)
3. The position indicator according to claim 1, characterized in
that: the signal level of the enhanced signal generated by the
signal enhancing processing circuit is increased in at least one of
a region of a rising edge of a waveform of the enhanced signal and
a region of a falling edge of the waveform of the enhanced
signal.
4. The position indicator according to claim 1, characterized in
that: the enhanced signal generated by the signal enhancing
processing circuit results from performing determined phase control
on the AC signal received via the first electrode.
5. The position indicator according to claim 4, characterized in
that: the determined phase control is compensation for a phase of
the AC signal received via the first electrode.
6. The position indicator according to claim 1, characterized in
that: the signal enhancing processing circuit subjects a signal
waveform of the AC signal received via the first electrode to
waveform conversion.
7. The position indicator according to claim 6, characterized in
that: the signal enhancing processing circuit converts the signal
waveform of the AC signal received via the first electrode into a
rectangular waveform.
8. The position indicator according to claim 1, characterized in
that: the signal enhancing processing circuit includes a variable
signal amplification factor circuit configured to control a signal
level of the AC signal received via the first electrode.
9. The position indicator according to claim 8, characterized in
that: the variable signal amplification factor circuit is an
automatic gain adjusting circuit configured to output a signal
having a constant signal level against variations in the signal
level of the AC signal received via the first electrode.
10. The position indicator according to claim 9, characterized in
that: the variable signal amplification factor circuit is a
manually variable amplification factor circuit configured to
increase the signal level of the AC signal received via the first
electrode with a determined amplification factor.
11. The position indicator according to claim 1, characterized in
that: a shielding member is disposed between the first electrode
and the second electrode for preventing electrical interference
therebetween.
12. The position indicator according to claim 11, characterized in
that: the shielding member surrounds at least one electrode of the
first electrode and the second electrode, and is electrically
grounded.
13. The position indicator according to claim 11, characterized in
that: the position indicator has a shape of a stylus and the second
electrode is disposed so as to surround the first electrode, and
the shielding member surrounds the first electrode and is disposed
between the first electrode and the second electrode.
14. The position indicator according to claim 13, characterized in
that: one end section of the shielding member is disposed so as to
project from the second electrode in a longitudinal direction of
the position indicator, and a collar section is formed at the one
end section.
15. The position indicator according to claim 1, characterized by
further comprising a connection changing circuit configured to
switch the first electrode and the second electrode with each other
as an electrode for signal reception and an electrode for signal
transmission.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority under 35 U.S.C.
.sctn.119(a) of Japanese Application No. 2010-278002, filed Dec.
14, 2010, the entire content of which is incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates to a position indicator used
in conjunction with a position detecting sensor in which position
detection is carried out by detecting a change in capacitance.
BACKGROUND ART
[0003] In general, a capacitance type position detecting sensor in
which position detection is carried out by detecting a change in
capacitance needs a certain level of capacitance or higher
(normally about 1 pF) that occurs between the position detecting
sensor and a position indicator in order to detect the position of
the position indicator with high accuracy. Thus, an input operation
on the position detecting sensor is performed by a fingertip or a
dedicated electrostatic pen having a relatively large area at a
time of contact. That is, it is difficult from a viewpoint of
detection sensitivity to detect a fine input position on the
position detecting sensor by an electrostatic pen in the shape of a
stylus having a fine tip.
[0004] Various techniques for solving this problem have
conventionally been proposed. For example, Patent Document 1
(Japanese Patent Laid-Open No. Hei 7-295722) and Patent Document 2
(Japanese Patent Laid-Open No. Hei 8-272509) disclose a coordinate
input device that has an alternating-current (AC) signal generator
within a position indicator, and which detects the position of the
position indicator by detecting a signal corresponding to the AC
signal sent out from the position indicator in a position detecting
sensor. In these Patent Documents 1 and 2, the AC signal sent out
from the position indicator to the position detecting sensor has a
large amplitude, thereby enabling position detection even with the
position indicator formed by an electrostatic pen having a fine
tip.
[0005] Specifically, Patent Document 1 shows a structure in which a
signal oscillator 1 is provided within a signal pen 5, an AC signal
of a large amplitude is generated by the signal oscillator 1, and
the generated AC signal is applied between a stylus conductor 3 and
a ring-shaped conductor 4 in the tip section of the signal pen 5.
Patent Document 2 shows a structure in which a sine wave generator
is provided in a stylus 6, and a sine wave AC signal is boosted by
using a transformer and then supplied to a tip 2 of the stylus.
[0006] Patent Document 3 (Japanese Patent Laid-Open No.
2007-183809) shows the following structure. When a tip section 2 of
a stylus input device 1 touches the surface of a capacitance type
touch panel 51, a movable contact of a switching circuit 3 is
switched to the side of a fixed contact 3a, and a phase comparator
5 is set in an operating state. As a result, an AC reference signal
Vi of a frequency Fo, which signal is generated by a reference
signal source 54 in a capacitance detection type coordinate input
device 50, is received via the tip section 2, and then supplied to
one input of the phase comparator 5 via the fixed contact 3a of the
switching circuit 3. Because of this structure, a PLL circuit
including the phase comparator 5 is phase-synchronized with the AC
reference signal Vi, and outputs a signal of the same frequency as
that of the AC reference signal Vi. When the movable contact of the
switching circuit 3 is switched to a fixed contact 3b, the phase
comparator 5 is set in a non-operating state. However, the stylus
input device 1 outputs a signal that is phase-synchronized with and
having the same frequency as that of the AC reference signal Vi,
which is generated in the reference signal source 54 in the
capacitance detection type coordinate input device 50 due to a
flywheel effect of the PLL circuit. A signal having an opposite
phase from the output signal and an amplitude Vneg exceeding a
power supply voltage Vcc is output via the tip section 2 of the
stylus input device 1.
PRIOR ART DOCUMENT
Patent Document
[0007] [Patent Document 1] [0008] Japanese Patent Laid-Open No. Hei
7-295722 [0009] [Patent Document 2] [0010] Japanese Patent
Laid-Open No. Hei 8-272509 [0011] [Patent Document 3] [0012]
Japanese Patent Laid-Open No. 2007-183809
SUMMARY OF THE INVENTION
[0013] However, the position indicators described in Patent
Document 1 and Patent Document 2 have an AC signal generator, and
have the structure of unidirectional signal transmission for
transmitting the AC signal generated in the generator to the
position detecting sensor. Thus, the position indicator need to
have the AC signal generator adapted to the AC signal used by the
position detecting sensor. Cost is correspondingly increased, and
the position indicator compatible with the respective position
detecting sensor need to be provided, so that the versatility of
the position indicator is impaired.
[0014] The position indicator to which the techniques of Patent
Document 3 are applied has a structure of so-called half-duplex
communication, in which an AC signal from the position detecting
sensor is received by a conductor in the tip of the pen, and an AC
signal synchronized with the received signal is generated and sent
out from the same conductor in the tip of the pen to the position
detecting sensor. That is, in the position indicator of Patent
Document 3, the conductor in the tip of the pen is shared for both
the reception and transmission of the AC signals, so that reception
and transmission cannot be performed simultaneously, and a switch
circuit for switching the tip of the pen for a signal receiving
period and a signal transmitting period needs to be provided.
[0015] In addition, in the position indicator of Patent Document 3,
an output AC signal in opposite phase from and in synchronism with
the received AC signal is generated by the PLL circuit only in the
signal receiving period. Then, in the signal transmitting period,
the signal from the PLL circuit is output as the output AC signal.
Thus, signal continuity or phase relation between the received AC
signal and the output AC signal may not necessarily be
guaranteed.
[0016] As described above, the position indicator of Patent
Document 3 has a structure for generating a new signal
corresponding to the received AC signal by using the PLL circuit,
and thereafter sending out the signal generated by the PLL circuit
using the same conductor in the tip of the pen by switching the
switch circuit. Thus, because the position indicator of Patent
Document 3 includes the switch circuit, the continuity or real-time
characteristic of the output AC signal may be impaired. In
addition, because the PLL circuit generates a new signal, waveform
correlation between the signal waveform of the input signal and the
signal waveform of the output signal may not necessarily be
guaranteed.
[0017] In view of the above points, according to one aspect of the
present invention, a position indicator is provided that has a high
affinity to a position detecting sensor, has high versatility, and
ensures a determined waveform correlation between an input signal
and an output signal, by having a structure of so-called
full-duplex communication in which a signal input channel and a
signal output channel are present independently of each other. The
position indicator is to be used in conjunction with the position
detecting sensor that carries out position detection by detecting a
change in capacitance.
[0018] In order to solve the above-described problems, a position
indicator according to the present invention is a position
indicator for use in conjunction with a position detecting sensor
for carrying out position detection by detecting a change in
capacitance, and the position indicator includes the following: a
first electrode configured to receive an AC signal from the
position detecting sensor; a signal enhancing processing circuit
configured to subject the AC signal received via the first
electrode to predetermined signal enhancing processing; and a
second electrode different from the first electrode, the second
electrode being supplied with a signal output from the signal
enhancing processing circuit. An enhanced signal is formed having a
determined correlation with the AC signal received via the first
electrode from the position detecting sensor, and the enhanced
signal is sent out to the position detecting sensor via the second
electrode.
[0019] The position detecting sensor detects a change in the
received signal of the AC signal at a position indicated by the
position indicator according to the present invention, and thereby
detects the position indicated by the position indicator. The
position indicator according to the present invention having the
above-described structure subjects the AC signal received from the
position detecting sensor via the first electrode to signal
enhancing processing by the signal enhancing processing circuit,
and then feeds back the AC signal to the position detecting sensor
via the second electrode.
[0020] Thus, in the position detecting sensor, the change in the
received signal of the AC signal at the position indicated by the
position indicator according to the present invention is increased,
so that sensitivity of detection of the position indicator in the
position detecting sensor is improved.
[0021] According to the present invention, it is possible to
provide a position indicator that has a simple configuration, has a
high affinity to a position detecting sensor, has high versatility,
and ensures a determined waveform correlation between an input
signal and an output signal, so that position detection can be made
with high sensitivity, as a position indicator for use in
conjunction with the position detecting sensor that carries out
position detection by detecting a change in capacitance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a diagram explaining a conceptual structure of a
first embodiment of a position indicator according to the present
invention and a processing operation of the position indicator.
[0023] FIGS. 2A, 2B, and 2C are diagrams showing an example of a
structure of the first embodiment of the position indicator
according to the present invention.
[0024] FIG. 3 is a circuit diagram showing an example of a signal
processing circuit in the first embodiment of the position
indicator according to the present invention.
[0025] FIG. 4 is a diagram explaining an example of a position
detecting sensor with which the position indicator according to the
present invention is used.
[0026] FIG. 5 is a diagram explaining another example of the
position detecting sensor with which the position indicator
according to the present invention is used.
[0027] FIG. 6 is a circuit diagram showing an example of a part of
a signal processing circuit in a second embodiment of the position
indicator according to the present invention.
[0028] FIG. 7 is a circuit diagram showing an example of a part of
a signal processing circuit in a third embodiment of the position
indicator according to the present invention.
[0029] FIG. 8 is a circuit diagram showing an example of a part of
a signal processing circuit in a fourth embodiment of the position
indicator according to the present invention.
[0030] FIG. 9 is a circuit diagram showing an example of a part of
a signal processing circuit in a fifth embodiment of the position
indicator according to the present invention.
[0031] FIG. 10A is a circuit diagram showing an example of a part
of a signal processing circuit in a sixth embodiment of the
position indicator according to the present invention, and FIGS.
10B and 10C are waveform charts of assistance in explaining the
example.
[0032] FIGS. 11A, 11B, and 11C are diagrams explaining other
examples of a shielding member interposed between a first electrode
and a second electrode in an embodiment of the position indicator
according to the present invention.
DESCRIPTION OF THE INVENTION
First Embodiment
[0033] Preferred embodiments of a position indicator according to
the present invention will hereinafter be described with reference
to the drawings. FIG. 1 is a diagram of assistance in generally
explaining a conceptual structure of a position indicator 1
according to a first embodiment of the present invention and a
processing operation of the position indicator 1. FIG. 1 shows a
state in which the position indicator 1 is positioned on a plate
surface of a capacitance type position detecting sensor 2. FIGS. 2A
to 2C are diagrams of assistance in explaining an example of a
detailed configuration of the position indicator 1. FIG. 2A is a
partial longitudinal sectional view of the position indicator 1 and
FIG. 2B is a partial enlarged view of FIG. 2A. FIG. 2C is a diagram
showing a part of an external appearance of the position indicator
1. In the present embodiment, the position indicator 1 is formed as
a position indicator whose external appearance has the form of a
stick-shaped stylus.
[0034] The position indicator 1 according to the present embodiment
has a stick-shaped casing 3. This casing 3 is formed by a hollow
cylindrical-shaped insulator section 31 made of an insulating
material, for example a synthetic resin. In the present embodiment,
at least a part of an outer peripheral surface of the insulator
section 31 of the casing 3, by which part the position indicator 1
is held by an operator, is covered by a conductor section 32 made
of a metal, for example.
[0035] A printed wiring board 41 is provided within the casing 3.
The conductor section 32 covering the outer peripheral surface of
the casing 3 is electrically connected to a grounding conductor of
the printed wiring board 41.
[0036] A signal processing circuit 4 (FIG. 1) is formed on the
printed wiring board 41. As shown in FIG. 2A, the signal processing
circuit 4 formed on the printed wiring board 41 includes a
plurality of electronic parts formed by a resistor, a capacitor, an
IC (Integrated Circuit), and the like, wiring patterns such as
conducting patterns 42a and 42b and the like, a transformer 43 to
be described later, and the like as well as a power supply switch
44, an LED (Light Emitting Diode) 45 and the like in the present
example.
[0037] In the present embodiment, a battery 5 is formed so as to be
able to be housed within the casing 3. A power supply voltage of
the signal processing circuit 4 is generated in the battery 5. A
terminal 52 in FIG. 2A is a terminal connected electrically to a
power supply circuit included in the signal processing circuit 4 on
the printed wiring board 41. The cathode side electrode 51 of the
battery 5 is electrically connected to the terminal 52 in a state
of being in contact with the terminal 52. Though not shown, an
anode side electrode of the battery 5 is directly connected to the
grounding conductor of the printed wiring board 41, or brought into
pressed-contact with a terminal, which undergoes elastic
displacement and is connected to the grounding conductor of the
printed wiring board 41 via the conductor section 32 of the casing
3.
[0038] As shown in FIG. 2C, an operating element 44a of the power
supply switch 44 disposed on the printed wiring board 41 is
provided so as to be externally operable through an opening
provided in the casing 3. The power supply switch 44 can be turned
on or off by sliding movement of the operating element 44a by a
user.
[0039] The position indicator 1 is configured such that the LED 45
is lit when power is turned on by turning on the power supply
switch 44 by an operation of the operating element 44a, and such
that the LED 45 is deactivated when the power is turned off by
turning off the power supply switch 44. A translucent member 45L is
provided at a position corresponding to the position of the LED 45
in the outer peripheral surface of the casing 3. The user can check
whether the LED 45 is lit or not through the translucent member
45L.
[0040] In addition, a slide operating section 46 is provided in the
outer peripheral surface of the casing 3, for allowing a user to
manually change the resistance value of a variable resistor 422
provided in the signal processing circuit (FIG. 3), to be described
later.
[0041] A tapered section 33 that gradually tapers off is formed on
one end side in the direction of a center line of the hollow
cylindrical-shaped insulator section 31 forming the casing 3. A
peripheral electrode 6 made of a ring-shaped conducting metal, for
example, is attached to the outer circumference side of the tapered
section 33. Incidentally, the peripheral electrode 6 and the
conductor section 32 on the outer peripheral surface of the casing
3 are insulated from each other by the interposition of the
insulator section 31 between the peripheral electrode 6 and the
conductor section 32.
[0042] The peripheral electrode 6 forms a first electrode in the
present example. The peripheral electrode 6 is electrically
connected to the conducting pattern 42a on the printed wiring board
41 by a lead conducting member 61 penetrating through the insulator
section 31. The conducting pattern 42a in the present example is
connected to an input terminal of the signal processing circuit
4.
[0043] In addition, in the present embodiment, a central electrode
7 is provided so as to project from a hollow part of the tapered
section 33 to the outside. The central electrode 7 includes for
example a stick-shaped conductor 71 made of a conductive metal and
an elastic protective conductor 72 provided at an end of the
stick-shaped conductor 71. The stick-shaped conductor 71 is
provided so as to penetrate from the position of the printed wiring
board 41 within the casing 3 through the hollow part of the tapered
section 33 and project to the outside. The elastic protective
conductor 72 is a member for preventing the indicating input
surface of the position detecting sensor 2 from being scratched and
for increasing the area of contact of the position indicator 1 with
the indicating input surface when the position indicator 1 is in
contact with the position detecting sensor 2. The elastic
protective conductor 72 is formed by a conductive elastic rubber in
the present example. Incidentally, this elastic protective
conductor 72 may be omitted. In this case, the stick-shaped
conductor 71 is desirably formed by a conductive elastic member,
for example.
[0044] The central electrode 7 forms a second electrode in the
present example. An end part of the stick-shaped conductor 71 on an
opposite side from the side where the elastic protective conductor
72 is provided is fixed to the printed wiring board 41, and is
electrically connected to the conducting pattern 42b. The
conducting pattern 42b in the present example is connected to an
output terminal of the signal processing circuit 4.
[0045] In addition, a shielding member 8 for effectively preventing
an electrical interference between the peripheral electrode 6 and
the central electrode 7 is provided between the peripheral
electrode 6 and the central electrode 7. In the present embodiment,
the shielding member 8 is provided so as to surround the central
electrode 7. Thereby, the shielding member 8 is interposed between
the peripheral electrode 6 and the central electrode 7 to minimize
a coupling capacitance between the peripheral electrode 6 and the
central electrode 7.
[0046] As shown in FIG. 2B, which is a partial enlarged view of
FIG. 2A, the shielding member 8 is formed by a tubular conductor 81
made of a conducting metal having an insulating layer 82 formed on
an inner wall surface of the tubular conductor 81. The tubular
conductor 81 is electrically connected to the grounding conductor
of the printed wiring board 41.
[0047] The stick-shaped conductor 71 of the central electrode 7 is
housed within a hollow part of the tubular conductor 81 having the
insulating layer 82 on the inner wall surface of the tubular
conductor 81, whereby the central electrode 7 is surrounded by the
shielding member 8. In the example of FIG. 2B, a part of the
elastic protective conductor 72 of the central electrode 7 is also
surrounded by the tubular conductor 81 of the shielding member
8.
[0048] The peripheral electrode 6 and the tubular conductor 81 of
the shielding member 8 are insulated from each other by the
interposition of the tapered section 33 of the insulator section 31
between the peripheral electrode 6 and the tubular conductor 81.
The central electrode 7 and the tubular conductor 81 of the
shielding member 8 are insulated from each other by the
interposition of the insulating layer 82 on the inner wall surface
of the tubular conductor 81 of the shielding member 8 between the
central electrode 7 and the tubular conductor 81.
[0049] Incidentally, while only the central electrode 7 is shielded
in the example of FIG. 2B, the peripheral electrode 6 may be
shielded instead. Alternatively, both of the peripheral electrode 6
and the central electrode 7 may be shielded.
[0050] In addition, while shielding is provided by surrounding the
entire stick-shaped conductor 71 of the central electrode 7 with
the shielding member 8, it suffices to interpose the shielding
member in at least a part where the peripheral electrode 6 and the
central electrode 7 are in proximity to each other.
[0051] An example of configuration of the signal processing circuit
4 will next be described. FIG. 3 is a diagram showing an example of
circuit configuration of the signal processing circuit 4. The
signal processing circuit 4 in the present example includes a power
supply circuit section 40a and a signal processing section 40b. The
power supply circuit section 40a includes a DC-to-DC converter 401.
The DC-to-DC converter 401 generates a power supply voltage +Vcc
from the voltage of the battery 5, and supplies the power supply
voltage +Vcc to the signal processing section 40b.
[0052] The power supply circuit section 40a has a power supply
switch 44 between the DC-to-DC converter 401 and the battery 5. In
addition, a series circuit of a resistance 402 and the LED 45 is
connected between the output terminal of the DC-to-DC converter 401
and the grounding conductor. Further, the output terminal of the
DC-to-DC converter 401 is connected to the grounding conductor via
a series connection of a resistance 403 and a resistance 404. A
reference voltage Vref (=Vcc/2) is output from the point of
connection between the resistance 403 and the resistance 404.
[0053] As described above, when the power supply switch 44 is
turned on by operating the operating element 44a provided in the
casing 3, the voltage of the battery 5 is supplied to the DC-to-DC
converter 401, where the power supply voltage Vcc is generated, and
at the same time, the LED 45 is lit to inform the user that the
power is on. When the power supply switch 44 is turned off by
operating the operating element 44a, the supply of the voltage of
the battery 5 to the DC-to-DC converter 401 is stopped, the
generation of the power supply voltage Vcc is stopped, and the LED
45 is turned off to inform the user that the power is off.
[0054] The signal processing section 40b forms a signal enhancing
processing circuit. The signal processing section 40b in the
present embodiment includes a sense amplifier 410, a variable
signal amplification factor circuit 420, and a transformer 43.
[0055] Signal enhancing processing performed in the signal
enhancing processing circuit in the present invention includes not
only processing for amplifying the signal level of an input signal
to a determined signal level but also processing for modifying the
waveform of the input signal or processing for controlling the
phase of the input signal. For example, when the input signal has a
signal waveform such as that of a sine wave or the like, the signal
enhancing processing includes increasing a rate of change of the
signal level of the input signal in a region where the signal level
is low and decreasing the rate of change in a region where the
signal waveform is at a maximum value or a minimum value. When the
input signal has a signal waveform such as that of a rectangular
wave or the like, the signal enhancing processing includes forming
the signal waveform into a steep signal waveform by increasing a
rate of change of the signal level of the input signal in a region
of a rising edge of the signal waveform or a region of a falling
edge of the signal waveform, or increasing amplitude level in the
region. Further, compensation for a phase difference with respect
to the input signal, or phase control performed so as to retain a
predetermined phase difference, can be applied. In the signal
enhancing processing circuit, signal enhancing processing is
performed with each of such signal processing methods combined with
the above-described signal level amplifying processing, or with
each of such signal processing methods applied independently of the
signal level amplifying processing.
[0056] In the present example, the sense amplifier 410 includes an
operational amplifier 411 and a capacitor 412 connected between the
inverting input terminal and the output terminal of the operational
amplifier 411. The inverting input terminal of the operational
amplifier 411 is connected to a connecting terminal 413 connected
to the peripheral electrode 6. In addition, the non-inverting input
terminal of the operational amplifier 411 is supplied with the
above-described reference voltage Vref.
[0057] When the position indicator 1 is on the position detecting
sensor 2, the peripheral electrode 6 of the position indicator 1
and the position detecting sensor 2 are coupled to each other via a
capacitance C1, as shown in FIG. 1. As will be described later, an
alternating-current (AC) signal (i.e., a current based on an
alternating voltage) flows in the position detecting sensor 2.
Thus, the AC signal is supplied as a current signal to the
connecting terminal 413 via the capacitance C1 and the peripheral
electrode 6, and input to the sense amplifier 410. The capacitor
412 is to detect the current signal input via the capacitance C1.
In the present invention, the AC signal may have any waveform. AC
signals of any waveform, such as rectangular wave signals, sine
wave signals and the like, can be input.
[0058] Then, the sense amplifier 410 inverts the phase of the AC
signal input as current signal via the connecting terminal 413, and
outputs the resulting AC signal to the variable signal
amplification factor circuit 420.
[0059] The variable signal amplification factor circuit 420
includes an operational amplifier 421 and a variable resistor 422
connected between the inverting input terminal and the output
terminal of the operational amplifier 421. The resistance value of
the variable resistor 422 is variably controlled by the user
manually by sliding movement of the slide operating section 46
shown in FIG. 2C. Then, by variably setting the resistance value of
the variable resistor 422 manually, the amplification factor of the
variable signal amplification factor circuit 420 is variably set.
As a result, the signal detection sensitivity of the position
indicator is controlled.
[0060] The AC signal amplified by the variable signal amplification
factor circuit 420 is supplied to the primary winding 43a of the
transformer 43. A ratio between the number of turns n1 of the
primary winding 43a of the transformer 43 and the number of turns
n2 of the secondary winding 43b of the transformer 43 is set such
that the number of turns on the side of the secondary winding 43b
is larger (n1<n2), such as n1:n2=1:10, for example. Thus, on the
side of the secondary winding 43b of the transformer 43, the
amplitude of an output signal of the variable signal amplification
factor circuit 420 is multiplied according to the turns ratio, so
that an AC signal (voltage signal) of large amplitude is
obtained.
[0061] One end of the secondary winding 43b of the transformer 43
is connected to a connecting terminal 423 connected to the
stick-shaped conductor 71 of the central electrode 7 shielded by
the shielding member 8. Another end of the secondary winding 43b of
the transformer 43 is connected to the grounding conductor of the
printed wiring board 41. Thus, an output signal set as an AC signal
voltage of large amplitude by the signal processing section 40b is
supplied to the central electrode 7 via the connecting terminal
423.
[0062] When the position indicator 1 is on the position detecting
sensor 2, the central electrode 7 of the position indicator 1 and
the position detecting sensor 2 are coupled to each other via a
capacitance. Therefore the AC signal is fed back from the position
indicator 1 to the position detecting sensor 2 via the central
electrode 7 of the position indicator 1.
[0063] Description will next be made of the capacitance type
position detecting sensor 2 in the present example. The capacitance
type position detecting sensor 2 in the present example has the
configuration of a position detecting sensor of a mutual
capacitance system, in which a sensor electrode is composed of an
input electrode and an output electrode, and a change in the
coupling capacitance of a touch point touched by the position
indicator 1 is detected.
[0064] Specifically, as shown in FIG. 4, the position detecting
sensor 2 in the present example includes a sensor section 20, a
transmitting section 21, and a receiving section 22. The sensor
section 20 includes a plurality of linear transmitting conductors,
or 64 transmitting conductors 23Y.sub.1, 23Y.sub.2, . . . ,
23Y.sub.64 in the present example, that extend in a lateral
direction (X-axis direction) of the indicating input surface as
well as a plurality of receiving conductors, or 64 receiving
conductors 24X.sub.1, 24X.sub.2, . . . , 24X.sub.64 in the present
example, that are orthogonal to the transmitting conductors
23Y.sub.1 to 23Y.sub.64 and which extend in a longitudinal
direction (Y-axis direction) of the indicating input surface. The
plurality of transmitting conductors 23Y.sub.1 to 23Y.sub.64 are
arranged at equal intervals in the Y-axis direction, and are
connected to the transmitting section 21. The plurality of
receiving conductors 24X.sub.1 to 24X.sub.64 are arranged at equal
intervals in the X-axis direction, and are connected to the
receiving section 22.
[0065] Incidentally, when the 64 transmitting conductors 23Y.sub.1
to 23Y.sub.64 do not need to be individually distinguished from
each other in the description of the transmitting conductors in the
present specification, the transmitting conductors 23Y.sub.1 to
23Y.sub.64 will be referred to as transmitting conductors 23Y.
Similarly, when the 64 receiving conductors 24X.sub.1 to 24X.sub.64
do not need to be individually distinguished from each other in the
description of the receiving conductors, the receiving conductors
24X.sub.1 to 24X.sub.64 will be referred to as receiving conductors
24X.
[0066] The plurality of transmitting conductors 23Y are for example
formed in a plane on the lower side of a substrate. The plurality
of receiving conductors 24X are formed in a plane on the upper side
of the substrate. Thus, the plurality of transmitting conductors
23Y and the plurality of receiving conductors 24X are arranged at a
predetermined distance corresponding to a predetermined thickness
of the substrate, have an arrangement relation in which the
plurality of transmitting conductors 23Y and the plurality of
receiving conductors 24X are orthogonal to each other, and form a
plurality of points of intersection (cross points). A transmitting
conductor 23Y and a receiving conductor 24X at each cross point can
be considered to be coupled to each other via a predetermined
capacitance.
[0067] The transmitting section 21 supplies a predetermined AC
signal to the transmitting conductors 23Y. In this case, the
transmitting section 21 may supply an identical AC signal to the
plurality of transmitting conductors 23Y.sub.1, 23Y.sub.2, . . . ,
23Y.sub.64 while sequentially selecting the plurality of
transmitting conductors 23Y.sub.1, 23Y.sub.2, . . . , 23Y.sub.64
one at a time, or may simultaneously supply a plurality of AC
signals different from each other to the plurality of transmitting
conductors 23Y.sub.1, 23Y.sub.2, . . . , 23Y.sub.64. In addition,
the plurality of transmitting conductors 23Y.sub.1, 23Y.sub.2, . .
. , 23Y.sub.64 may be divided into a plurality of groups, and
different AC signals may be used in different groups.
[0068] The receiving section 22 detects a signal component
resulting from the AC signal supplied to the transmitting
conductors 23Y being transmitted to each of the receiving
conductors 24X.sub.1, 24X.sub.2, . . . , 24X.sub.64 via the
predetermined capacitance. Supposing that coupling capacitances
between the transmitting conductors 23Y and the receiving
conductors 24X are equal to each other at all the cross points, the
receiving section 22 detects a received signal at a predetermined
level from all the receiving conductors 24X.sub.1, 24X.sub.2, . . .
, 24X.sub.64 of the sensor section 20 when the position indicator 1
is not present on the sensor section 20.
[0069] When the position indicator 1 touches the sensor section 20,
on the other hand, a transmitting conductor 23Y and a receiving
conductor 24X forming a cross point at the contact position and the
position indicator 1 are coupled to each other via a capacitance.
That is, the capacitance at that cross point is changed by the
position indicator 1, and the level of a received signal obtained
from the receiving conductor 24X at the cross point where the
position indicator 1 is present is changed from that of the other
cross points.
[0070] The receiving section 22 detects the position of the
position indicator 1 by sensing the receiving conductor 24X whose
received signal is changed in level among the plurality of
receiving conductors 24X.sub.1, 24X.sub.2, . . . , 24X.sub.64.
Then, a control section of the position detecting sensor 2 (not
shown in the figures) detects the cross point touched by the
position indicator 1 by detecting the transmitting conductor 23Y,
to which the AC signal is supplied from the transmitting section
21, and the receiving conductor 24X whose received signal is
changed in level in the receiving section 22.
[0071] Also when a finger rather than the position indicator 1 has
approached or touched the sensor section 20, the position detecting
sensor 2 detects a cross point approached or touched by the finger
on similar principles. In this case, a part of the AC signal
supplied to a transmitting conductor 23Y flows through the finger
and the human body of the user to the ground. Therefore, a signal
received by a receiving conductor 24X forming the cross point where
the finger is present is changed in level. The receiving section 22
detects the receiving conductor 24X forming the cross point where
the finger is present by detecting the change in level of the
received signal.
[0072] Also in the case of the position indicator in the shape of a
stylus, the position detecting sensor can detect an indicated
position on the sensor section 20 on similar principles to those of
detection of a finger position. However, as described earlier, in
the case of the position indicator in the shape of a stylus, an
area of contact between the position indicator and the position
detecting sensor is not so large as in the case of a finger, thus
resulting in a low coupling capacitance and low detection
sensitivity of the position detecting sensor.
[0073] On the other hand, as will be described below, the position
indicator 1 according to the present embodiment has a high affinity
to the position detecting sensor 2, has high versatility, and
ensures a determined waveform correlation between an input signal
and an output signal, so that position detection on the sensor
section 20 can be made with high sensitivity.
[0074] Specifically, as shown in FIG. 1, when the position
indicator 1 according to the present embodiment is brought into
proximity or contact with the sensor section 20 of the position
detecting sensor 2, the peripheral electrode 6 and the sensor
section 20 are coupled to each other via the capacitance C1. Then,
the AC signal supplied to a transmitting conductor 23Y is input as
a current signal to the signal processing circuit 4 via the
capacitance C1, the peripheral electrode 6, and the connecting
terminal 413.
[0075] The AC signal (current signal) input to the signal
processing circuit 4 is subjected to signal enhancing processing by
being subjected to phase inversion in the sense amplifier 410 of
the signal processing section 40b, and thereafter being amplified
in the variable signal amplification factor circuit 420 and boosted
(multiplied) by the transformer 43, and supplied as a voltage
signal to the central electrode 7 via the connecting terminal 423.
That is, the AC signal input from the sensor section 20 to the
signal processing circuit 4 via the peripheral electrode 6 is
converted into a signal of opposite phase and large amplitude in
the signal processing section 40b, and fed back to the sensor
section 20 via the central electrode 7.
[0076] In this case, the AC signal fed back from the central
electrode 7 in the position indicator 1 to the sensor section 20 in
the position detecting sensor 2 is an enhanced signal of opposite
phase from the AC signal supplied to the transmitting conductor
23Y. The position indicator 1 therefore functions to further
increase a change in the AC signal in the signal received by the
receiving conductor 24X. The position detecting sensor 2 can thus
detect the contact position of the position indicator 1 with high
sensitivity. Incidentally, detecting operation is further
stabilized when the ground of the position indicator 1 is connected
to a human body. Specifically, in the present embodiment, the
casing 3 of the position indicator 1 is covered with the conductor
section 32 connected to the grounding conductor of the printed
wiring board 41 on which the signal processing circuit 4 is formed.
Thus, the AC signal supplied to the transmitting conductor 23Y in
the position detecting sensor 2 flows to the ground through the
position indicator 1 and the human body of the user, whereby signal
detecting operation can be further stabilized.
[0077] Letting V be the voltage of the transmitting conductor 23Y
of the sensor section 20 in the position detecting sensor 2, e be
the voltage of the central electrode 7 in the position indicator 1
according to the present embodiment, and C2 be a capacitance
between the peripheral electrode 6 and the central electrode 7 (see
FIG. 1), there is a relation:
e.ltoreq.C1/C2V
It is therefore advantageous to minimize the capacitance C2 between
the peripheral electrode 6 and the central electrode 7 in raising
the potential e of the central electrode 7.
[0078] For this, in the position indicator 1 according to the
present embodiment, the shielding member 8 is interposed between
the peripheral electrode 6 and the central electrode 7, whereby
coupling between the peripheral electrode 6 and the central
electrode 7 is minimized. Thus, in the position indicator 1
according to the present embodiment, the interposition of the
shielding member 8 can reduce the capacitance C2 between the
peripheral electrode 6 and the central electrode 7, increase the
voltage e, and enhance sensitivity efficiently.
[0079] In addition, in the position indicator 1 according to the
present embodiment, the user manually adjusts the slide operating
section 46 to vary the resistance value of the variable resistor
422 and to thus variably set the amplification factor of the
variable signal amplification factor circuit 420, whereby
sensitivity of detection of a position indicated by the position
indicator 1 in the position detecting sensor 2 can be adjusted.
[0080] Specifically, in a state of the central electrode 7 of the
position indicator 1 lightly touching the surface of the sensor
section 20 of the position detecting sensor 2, an area of contact
of the sensor section 20 with the elastic protective conductor 72
at the end of the central electrode 7 is reduced. However, when the
amplification factor of the variable signal amplification factor
circuit 420 is increased by manually adjusting the slide operating
section 46, even in the case of the light touch, the position
detecting sensor 2 can detect the position indicator 1 with high
sensitivity.
[0081] Conversely, in a state of the central electrode 7 of the
position indicator 1 strongly touching the surface of the sensor
section 20 of the position detecting sensor 2, an area of contact
of the sensor section 20 with the elastic protective conductor 72
at the end of the central electrode 7 is increased. However, when
the amplification factor of the variable signal amplification
factor circuit 420 is decreased by manually adjusting the slide
operating section 46, even in the case of the strong touch, the
position detecting sensor 2 can detect the position indicator 1
stably as if the position indicator 1 is moderately touching the
sensor surface.
[0082] Incidentally, in the above-described embodiment, the
variable signal amplification factor circuit 420 of the signal
enhancing processing circuit is configured such that the
amplification factor can be changed continuously by the variable
resistor 422. However, the variable signal amplification factor
circuit 420 may be configured such that the amplification factor
can be changed stepwise by selecting a plurality of resistors
having different resistance values by a slide switch.
[0083] The position indicator 1 according to the first embodiment
described above is configured such that the peripheral electrode 6
is set as a first electrode to receive the AC signal from the
position detecting sensor 2 and such that the central electrode 7
is set as a second electrode to feed back an enhanced output AC
signal to the position detecting sensor 2. However, the central
electrode 7 may be set as the first electrode for receiving the AC
signal from the position detecting sensor 2, and the peripheral
electrode 6 may be set as the second electrode for feeding back an
enhanced output AC signal to the position detecting sensor 2.
Second Embodiment
[0084] In the position indicator 1 according to the first
embodiment described above, the first electrode is the peripheral
electrode 6, and the second electrode is the central electrode 7.
However, it has been found that this configuration causes the
following problems depending on the configuration of the position
detecting sensor 2.
[0085] In the position detecting sensor 2 used in the first
embodiment, the transmitting conductors 23Y and the receiving
conductors 24X are both linear conductors. On the other hand, a
sensor section 20A of a position detecting sensor 2A in the example
of FIG. 5 includes transmitting conductors 230Y.sub.1, 230Y.sub.2,
. . . , 230Y.sub.64 that do not have a linear shape but have a wide
width. Other configurations are similar to those of the first
embodiment. Specifically, receiving conductors of the sensor
section 20A are linear receiving conductors 24X.sub.1, 24X.sub.2, .
. . , 24X.sub.64 as in the first embodiment. In the sensor section
20A in the present example, the plurality of transmitting
conductors 230Y.sub.1, 230Y.sub.2, . . . , 230Y.sub.64 are
connected to a transmitting section 21, and the plurality of
receiving conductors 24X.sub.1, 24X.sub.2, . . . , 24X.sub.64 are
connected to a receiving section 22.
[0086] In the position detecting sensor 2A of such a configuration,
when a central electrode 7 is situated between two receiving
conductors 24X.sub.i and 24X.sub.i+1 adjacent to each other while
the position indicator 1 is moved in an oblique direction indicated
by a dotted line arrow in FIG. 5, because the second electrode for
feeding back an AC signal to the position detecting sensor 2A is
the central electrode 7, the central electrode 7 functions to feed
back a larger part of the AC signal to one of the receiving
conductors 24X.sub.1 and 24X.sub.1+1 that is closer to the central
electrode 7.
[0087] Thus, when the position indicator 1 is moved linearly in the
oblique direction, a problem occurs in that the position detecting
sensor 2A detects the locus of movement of the position indicator 1
as a meandering locus.
[0088] In order to remedy this problem, it suffices to set the
central electrode 7 in the position indicator as the first
electrode for receiving the AC signal from the position detecting
sensor 2A and set the peripheral electrode 6 in the position
indicator as the second electrode for feeding back an enhanced AC
signal to the position detecting sensor 2A.
[0089] Specifically, because the transmitting conductors
230Y.sub.1, 230Y.sub.2, . . . , 230Y.sub.64 are conductors having a
wide width, the AC signal can be received uniformly even when the
central electrode 7 is set as the first electrode for receiving the
AC signal. On the other hand, when the peripheral electrode 6 is
set as the second electrode for feeding back an enhanced AC signal
to the position detecting sensor 2, the peripheral electrode 6 has
a larger area of electric engagement with the position detecting
sensor 2 than the central electrode 7. Thus, even when the position
indicator is situated between two receiving conductors 24X.sub.i (i
is an integer equal to or more than one) (i=1, 2, . . . , 63, which
is true also in the following) and 24X.sub.i+1 adjacent to each
other, the peripheral electrode 6 and the two receiving conductors
24X.sub.i and 24X.sub.i+1 adjacent to each other can be
respectively set in substantially similar capacitive coupling
relations. Thus, even when the position indicator is moved in the
oblique direction as indicated by the dotted line arrow in FIG. 5,
the meandering of the locus of movement of the position indicator
is prevented, and the position detecting sensor 2A can sense the
locus of movement of the position indicator as a linear locus.
[0090] In consideration of the above, in the second embodiment, the
peripheral electrode 6 and the central electrode 7 of the position
indicator 1 can be switched to the second electrode and the first
electrode, respectively. FIG. 6 is a diagram showing a
configuration of a signal processing section 40bA of a signal
processing circuit 4A in a position indicator 1A according to the
second embodiment. In FIG. 6, the same parts as in the signal
processing section 40b of the signal processing circuit 4 according
to the first embodiment shown in FIG. 3 are identified by the same
reference numerals.
[0091] Specifically, in the signal processing section 40bA, a
connecting terminal 413 connected with the peripheral electrode 6
is connected to one input terminal 481a of a switch 481, and
connected to another input terminal 482b of a switch 482. In
addition, a connecting terminal 423 connected with the central
electrode 7 is connected to another input terminal 481b of the
switch 481, and connected to one input terminal 482a of the switch
482.
[0092] The movable contact 481c of the switch 481 is connected to
the inverting input terminal of an operational amplifier 411. The
movable contact 482c of the switch 482 is connected to one end of
the secondary winding 43b of a transformer 43. Otherwise, the
signal processing section 40bA is formed in the same manner as the
signal processing section 40b described earlier.
[0093] In addition, as shown in the vicinity of the connecting
terminal 413 in FIG. 6, a switching operating element 48 for
manually switching switches 481 and 482, which operate in an
interlocked manner with each other, is provided so as to be exposed
to the outside in a part of the casing 3 of the position indicator
1A according to the second embodiment.
[0094] When the user positions the switching operating element 48
to an "a" side by performing a sliding movement of the switching
operating element 48 in the direction of an arrow, the switches 481
and 482 are switched to the side of one input terminal 481a and the
side of one input terminal 482a in an interlocked manner. Then, the
connecting terminal 413 connected with the peripheral electrode 6
is connected to the inverting input terminal of the operational
amplifier 411, and the connecting terminal 423 connected with the
central electrode 7 is connected to one end of the secondary
winding 43b of the transformer 43, so that the position indicator
1A operates in the same manner as in the first embodiment.
[0095] When the user positions the switching operating element 48
to a "b" side, on the other hand, the switches 481 and 482 are
switched to the side of the other input terminal 481b and the side
of the other input terminal 482b in an interlocked manner. Then,
the connecting terminal 423 connected with the central electrode 7
is connected to the inverting input terminal of the operational
amplifier 411, and the connecting terminal 413 connected with the
peripheral electrode 6 is connected to one end of the secondary
winding 43b of the transformer 43.
[0096] Thus, a part of the AC signal from the position detecting
sensor 2A is input to the signal processing circuit 4A of the
position indicator 1A via the central electrode 7. Then, the AC
signal set in opposite phase and enhanced by the signal processing
section 40bA is fed back to the position detecting sensor 2A via
the peripheral electrode 6. Thereby, as in the first embodiment,
the position detecting sensor 2A can detect a position indicated by
the position indicator 1A with high sensitivity.
[0097] The transmitting conductors and the receiving conductors of
the position detecting sensor are not limited to the above
examples. Receiving conductors having a wide width or transmitting
conductors and receiving conductors both having a wide width may
also be used. According to the second embodiment, the user can
change the peripheral electrode 6 and the central electrode 7 to
the first electrode or the second electrode by the switching
operating element 48 according to differences in configuration of
these position detecting sensors. Thus, when the position indicator
according to the second embodiment is used, various position
detecting sensors having different configurations of transmitting
conductors and receiving conductors can detect the position
indicator whose dependence on the position detecting sensors is
reduced and which is highly versatile, with higher sensitivity,
while avoiding problems corresponding to the different
configurations.
Third Embodiment
[0098] In the above first and second embodiments, the signal
processing sections 40b and 40bA of the signal processing circuits
4 and 4A form a signal enhancing processing circuit with the
variable signal amplification factor circuit 420 provided in a
stage subsequent to the sense amplifier 410. However, the signal
enhancing processing circuit can be of other configurations.
[0099] A third embodiment is a first example of the signal
enhancing processing circuit, which enhances an output voltage
without using the variable signal amplification factor circuit 420.
FIG. 7 is a circuit diagram showing an example of configuration of
a signal processing section 40bB of a signal processing circuit 4B
in the case of a position indicator according to the third
embodiment.
[0100] As shown in FIG. 7, the signal processing section 40bB
includes a sense amplifier 410 and an enhancing circuit 430. The
enhancing circuit 430 includes a transformer 43 and an inverting
amplifier circuit 431. The output of the sense amplifier 410 is
supplied to one end side of the primary winding 43a of the
transformer 43 with polarity unchanged, while the output of the
sense amplifier 410 is also inverted in polarity by the inverting
amplifier circuit 431 and then supplied to the other end side of
the primary winding 43a of the transformer 43.
[0101] Specifically, because the output signal of the sense
amplifier 410 is supplied to both one end and the other end of the
primary winding 43a of the transformer 43 in opposite phases from
each other, the secondary winding 43b of the transformer 43 obtains
a signal as a result of amplifying the amplitude of the output
signal of the sense amplifier 410. Incidentally, a reference
voltage Vref is supplied to the respective non-inverting input
terminals of the operational amplifier 411 and the inverting
amplifier circuit 431.
[0102] Thus, according to the signal processing section 40bB
according to the third embodiment, the enhancing circuit 430 using
the transformer 43 can output a signal obtained by enhancing the
input signal to the enhancing circuit 430 even with a lower power
supply voltage.
[0103] Incidentally, in FIG. 7, phase and amplitude relation in the
case where the signal to be processed is a rectangular wave signal
is shown for reference. However, the waveform of the signal as an
object of processing in the signal processing section 40bB is not
limited to rectangular waves, but may be a signal of any waveform
such as that of a sine wave or the like as long as the signal is an
AC signal.
Fourth Embodiment
[0104] A fourth embodiment is a second example of realizing a
signal enhancing processing circuit without using the variable
signal amplification factor circuit 420. FIG. 8 is a circuit
diagram showing an example of configuration of a signal processing
section 40bC of a signal processing circuit 4C in the case of a
position indicator according to the fourth embodiment.
[0105] As shown in FIG. 8, the signal processing section 40bC
includes a sense amplifier 410 and a waveform converting circuit
440. In the example of FIG. 8, the waveform converting circuit 440
is formed by a comparator circuit 441. In the fourth embodiment,
the sense amplifier 410 has a high amplification factor, which may
be an amplification factor such that an output voltage value is
saturated, for example.
[0106] The comparator circuit 441 is a waveform converting circuit
for comparing an AC signal amplified to a large amplitude by the
sense amplifier 410 with a reference voltage Vref, and generating a
rectangular wave signal, which has a high level in a section where
the amplified signal level is equal to or higher than the reference
voltage Vref and which has a low level in other amplified signal
level sections.
[0107] The rectangular wave signal from the comparator circuit 441
is further multiplied (boosted) by a transformer 43, and then
output as an output signal of the signal processing section
40bC.
[0108] Thus, the signal processing section 40bC according to the
fourth embodiment can provide an enhanced output signal by
converting an input signal into a rectangular wave signal.
[0109] Incidentally, it is needless to say that a method for
converting the input signal into the rectangular wave signal is not
limited to a method represented in FIG. 8.
Fifth Embodiment
[0110] In the signal processing sections 40b and 40bA according to
the first and second embodiments described above, the variable
signal amplification factor circuit 420 in a stage subsequent to
the sense amplifier 410 is configured to allow the user to change
the amplification factor manually. However, the variable signal
amplification factor circuit 420 can be configured to control the
amplification factor automatically. The fifth embodiment is an
embodiment in that case. FIG. 9 is a circuit diagram showing an
example of a configuration of a signal processing section 40bD in
the fifth embodiment.
[0111] As shown in FIG. 9, the signal processing section 40bD
includes a sense amplifier 410 and an automatic gain adjusting
circuit 450. The automatic gain adjusting circuit 450 in the
present example includes a gain-controlled amplifier 451 of a
voltage-controlled type and an output level detecting circuit
452.
[0112] The output signal of the sense amplifier 410 is supplied to
the gain-controlled amplifier 451. Then, the output level detecting
circuit 452 detects the level of the output signal of the
gain-controlled amplifier 451, generates a gain adjusting voltage
for the gain-controlled amplifier 451, and supplies the gain
adjusting voltage to the control terminal of the gain-controlled
amplifier 451. The gain-controlled amplifier 451 is adjusted in
gain by the gain adjusting voltage from the output level detecting
circuit 452 so that the level of the output signal of the
gain-controlled amplifier 451 is constant at all times. Then, the
output signal of the gain-controlled amplifier 451 is boosted by a
transformer 43, and output as the output signal of the signal
processing section 40bD.
[0113] When indicating a position by holding the position indicator
1 in contact with the position detecting sensor 2, the user
performs an indicating operation according to the user's
preferences or the like, by for example holding the position
indicator 1 in strong contact with the position detecting sensor 2
or holding the position indicator 1 in light contact with the
position detecting sensor 2. However, according to the fifth
embodiment, the position detecting sensor 2 can detect the position
indicator 1 with optimum sensitivity at all times irrespective of
differences in the users' manner of indicating operations.
Sixth Embodiment
[0114] In the first to fifth embodiments described above, because a
current through a coupling capacitance occurring between the
position indicator 1 and the position detecting sensor 2 is the
input signal to the sense amplifier 410, the sense amplifier 410
uses a configuration in which the capacitor 412 is connected
between the input and output terminals of the operational amplifier
411, which is common with circuits of this kind.
[0115] In this configuration, however, the output signal of the
sense amplifier 410 has a blunted (dull) waveform based on the
input signal of the sense amplifier 410, and a phase delay occurs.
Thus, when the receiving section 22 in the position detecting
sensor 2 detects a change in a received signal, by detecting an AC
signal supplied to a transmitting conductor based on the received
signal obtained in a receiving conductor by synchronous detection
or correlation operation, it can be difficult to detect the change
with high accuracy.
[0116] The sixth embodiment is an example in which a signal
processing circuit is formed so as to be able to avoid this
problem. FIG. 10A is a circuit diagram showing an example of a
configuration of a signal processing section 40bE of a signal
processing circuit 4E in the sixth embodiment.
[0117] As with the signal processing section 40b according to the
first embodiment, the signal processing section 40bE of the signal
processing circuit 4E in the sixth embodiment includes a sense
amplifier 460 and a variable signal amplification factor circuit
420 as a signal enhancing processing circuit. However, in the sixth
embodiment, the sense amplifier 460 includes an operational
amplifier 461 and a resistor 462 connected between the inverting
input terminal and the output terminal of the operational amplifier
461. That is, this circuit configuration is equal to the
configuration in the first embodiment, except that the resistor 462
is connected in place of the capacitor 412 connected between the
inverting input terminal and the output terminal of the operational
amplifier 461. The signal processing section 40bE is otherwise
similar to the signal processing section 40b according to the first
embodiment.
[0118] According to the configuration of the signal processing
section 40bE according to the sixth embodiment, a coupling
capacitance between the position indicator 1 and the position
detecting sensor 2, and the resistor 462 connected between the
input and output terminals of the operational amplifier 461 in the
sense amplifier 460, together convert an AC signal input from the
position detecting sensor 2 to the position indicator 1 into a
signal in which high-frequency components are emphasized in the
sense amplifier 460. For example, when the AC signal supplied from
the transmitting section 21 in the position detecting sensor 2 is a
rectangular wave signal as shown in FIG. 10B, the waveform of the
output signal of the sense amplifier 460 is a differential waveform
whose rising edge and falling edge are emphasized, as shown in FIG.
10C.
[0119] In addition, at this time, because the resistor 462 is
connected to the input and output terminals of the operational
amplifier 461 in place of the capacitor 412, the output signal of
the sense amplifier 460 is a phase-compensated signal free from a
phase delay with respect to the input signal of the sense amplifier
460, as shown in FIGS. 10B and 10C. That is, the sense amplifier
460 including the operational amplifier 461 provided with the
resistor 462 functions also as a phase compensating circuit or a
phase control circuit.
[0120] As in the first embodiment, the output signal of the sense
amplifier 460 is supplied to the variable signal amplification
factor circuit 420 to be further enhanced. Then, the enhanced AC
signal is fed back from the position indicator 1 to the position
detecting sensor 2.
[0121] As is understood from the above description, the sense
amplifier in the sixth embodiment forms a high-frequency
emphasizing circuit, while also forming a phase compensating
circuit that eliminates a phase delay. Thus, according to the sixth
embodiment, even when the receiving section 22 in the position
detecting sensor 2 detects a change in a received signal by
detecting an AC signal supplied to a transmitting conductor based
on the received signal obtained in a receiving conductor by
synchronous detection or correlation operation, it is possible to
detect the change with high accuracy.
[0122] Incidentally, while description has been made of a case
where the AC signal used in the position detecting sensor 2 is a
rectangular wave signal with reference to FIGS. 10B and 10C, there
is no limitation to the waveform of the AC signal, and the AC
signal may be an AC signal of any waveform, such as a sine wave
signal or the like.
[0123] In addition, while the example of FIG. 10A is a case where
the sixth embodiment is applied to the sense amplifier of the
signal processing section 40b according to the first embodiment,
the sixth embodiment is also applicable to the sense amplifiers of
the signal processing sections according to the second to fifth
embodiments.
[Other Examples of Shielding Between Peripheral Electrode 6 and
Central Electrode 7]
[0124] As described in the first embodiment, a low capacitance
between the peripheral electrode 6 and the central electrode 7 is
favorable for improvement in sensitivity to the position indicator
1. Therefore, in the first embodiment, the capacitance between the
peripheral electrode 6 and the central electrode 7 is minimized by
surrounding the central electrode 7 with the shielding member
8.
[0125] In the first embodiment, as shown in FIGS. 2A to 2C, the
shielding member 8 is formed so as to penetrate through the
peripheral electrode 6 and cover the central electrode 7. That is,
the shielding member 8 is provided also over a part on the side of
the central electrode 7 penetrating beyond the peripheral electrode
6. However, it suffices for the shielding member 8 to exert a
shielding effect on at least a part where the peripheral electrode
6 and the central electrode 7 are in proximity to each other.
Therefore, as shown in FIG. 11A, the shielding member 8 may be
formed so as to cover the central electrode 7 in a position up to
an end part of the peripheral electrode 6 on the side of the
central electrode 7 or the vicinity of the end part.
[0126] In addition, to further reduce the capacitance between the
peripheral electrode 6 and the central electrode 7 by enhancing the
shielding effect, collar sections 8a and 8b may be formed at the
end part of the shielding member 8 penetrating the peripheral
electrode 6, as shown in FIGS. 11B and 11C. The effect of shielding
between the peripheral electrode 6 and the central electrode 7 can
be further enhanced by folding the collar section 8a so as to cover
the end part of the peripheral electrode 6 as shown in FIG. 11B, or
folding the collar section 8b so as to surround the central
electrode 7, as shown in FIG. 11C.
[0127] In addition, in the cases of FIGS. 11B and 11C, an air space
9 is interposed by providing an air gap between the collar sections
8a and 8b and the peripheral electrode 6 and the tapered section 33
formed of an insulating material. Thus, the effect of shielding
between the peripheral electrode 6 and the central electrode 7 can
be further enhanced. Incidentally, a predetermined dielectric may
be interposed in place of the air space 9. For example, the tapered
section 33 formed of a synthetic resin may be extended to the
collar sections 8a and 8b.
Other Embodiments and Examples of Modification
[0128] In the above embodiments, description has been made of a
capacitance type detecting sensor of a mutual capacitance system,
which only detects the coupling capacitance part (XY coordinates)
of a touch point between transmitting conductors, to which an AC
signal is input, and receiving conductors separated from the
transmitting conductors for receiving an AC signal. However, the
present invention is similarly applicable to a capacitance type
detecting sensor of a self-capacitance system in which the same
conductors are used for both inputting and outputting an AC
signal.
[0129] In addition, description has been made of a case where a
battery is used as a power supply for the position indicator.
However, power may for example be supplied from the side of the
capacitance type detecting sensor by a wireless system without a
battery being provided. For example, as described in Japanese
Patent Laid-Open No. 2007-164356, a configuration may be adopted,
in which a resonant circuit producing electromagnetic coupling with
a capacitance type detecting sensor and a capacitor, such as an
electric double layer capacitor or the like, are provided in a
position indicator, and a driving voltage for use is generated from
a voltage with which the capacitor is charged.
[0130] In addition, in the foregoing embodiments, a transformer for
increasing the signal level is provided on the output side of a
signal enhancing processing circuit. However, needless to say, a
signal enhancing circuit formed by a semiconductor circuit may be
provided in place of the transformer.
[0131] Incidentally, in the foregoing embodiments, the conductor
section 32 on the periphery of the casing 3 of the position
indicator is connected directly (in terms of a direct current) to
the grounding conductor of the printed wiring board 41 on which the
signal processing circuit 4 is formed within the casing of the
position indicator. However, coupling between the grounding
conductor of the internal circuit and the conductor section 32 may
be provided via a capacitor in terms of an alternating current.
[0132] In addition, in the foregoing embodiments, the conductor
section 32 is formed so as to cover substantially the entire
periphery of the casing 3 of the position indicator excluding a
part insulated from the peripheral electrode. However, a conductive
member such as a metallic sheet or the like connected to the
grounding conductor of the internal circuit may be disposed on only
a predetermined part of the casing 3 to be held by a user so as to
be in contact with the human body when the user operates the
position indicator.
[0133] In addition, when the casing 3 is formed by plastic, for
example, the conductor section 32 can be omitted by using a plastic
having conductivity and connecting the plastic to the grounding
conductor of the internal circuit in terms of a direct current or
in terms of an alternating current.
[0134] Incidentally, the position detecting sensor with which the
position indicator according to the present invention is used is
not limited to tablets, but may be various position detecting
sensors used in position detecting devices of various portable
terminals, such as pad type terminals and the like and other
stationary devices.
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