4. 15 A receiving device comprising: areceivingunitconfig~redtoreceiveanASK-modulated carrier signal; apositivedetectingunit configured to compare avoltage of the carrier signal with a positive threshold value, and 20 detect the larger one of the values as a positive amplitude fluctuation portion; a negative detecting unit configured to compare the voltageofthecarriersignalwithanegativethresholdvalue, and detect the smaller one of the vaiues as a negative amplitude 25 fluctuation portion; a combining unit configured to combine the positive amplitude fluctuation portion and the negative amplitude fluctuationportion ofthe voltage ofthe carrier signal; and a detecting unit configured to detect a result of the ', 30 combining of the positive amplitude fluctuation portion and the negative amplitude fluctuation portion.

5. The receiving device according to claim 9, further comprising: a shaping unit configured to shape the waveform of the 5 result ofthe combiningofthepositive amplitude fluctuation portion and the negative amplitude fluctuation portion into a sinusoidal wave, wherein the detecting unit detects the result of the shaped into the sinusoidal wave. Dated this 1 4m day of August, 201 3 ~SHRIMANTS ~ G H J OF REMFRY & SAGAR ATTORNEY FOR THE APPLICANT[S]

DESCRIPTION
SIGNAL PROCESSING DEVICE, SIGNAL PROCESSING METHOD, AND
RECEIVING DEVICE
5 TECHNICAL FIELD
[ OOOl]
This disclosure relates to signal processing
devices, signal processing methods, and receiving devices,
and more particularly, to a signal processing device, a
10 signal processing method, and a receiving device that are
suitable in cases where response information is detected
from a carrier signal load-modulated based on
transmission information, for example.
15 BACKGROUND ART
[0002]
Non-contact communication systems, such as FeliCa
(a registered trademark of Sony Corporation), are widely
used today. Such non-contact communication systems are
20 employed in the ticket gate systems for public
transportation such as trains and buses, and the
electronic money systems that can be used at various
kinds of shops and vending machines.
[0003]
25 Fig. 1 shows an example structure of a conventional
non-contact communication system. This non-contact
communication system 10 is formed with a reader/writer 11
and a transponder 12. In a case where this non-contact
communication system 10 is employed at a ticket gate of a
30 train station, for example, the reader/writer 11 is
installed in the ticket gate, and the transponder 12 is
embedded in an IC card serving as a ticket, such as Suica
(a trademark).
[0004]
In a case where predetermined transmission
5 information is transmitted from the reader/writer 11 to
the transponder 12, a sinusoidal carrier signal (a
carrier wave) like the signal shown in A of Fig. 2 is ASK
(amplitude shift keying)-modulated and transmitted in
accordance with the transmission information. In a case
10 where predetermined digitized response information like
the information shown in B of Fig. 2 is transmitted from
the transponder 12 to the reader/writer 11, on the other
hand, load modulation is performed to cause changes in
the voltage of the carrier signal as shown in C of Fig. 2
15 by switching on and off a damping resistor R1 in the
transponder 12 with a switch in accordance with the
predetermined response information (see Patent Document 1,
for example) .
[0005]
20 The load-modulated carrier signal is then received
by an antenna of the reader/writer 11. The received
load-modulated carrier signal has its degree of
modulation lowered in accordance with the distance
between the reader/writer 11 and the transponder 12, as
25 shown in D of Fig. 2. As the degree of modulation
becomes lower, detection of the response information
becomes more difficult.
[0006]
In a case where the non-contact communication
30 system 10 is used in a ticket gate at a train station or
the like, to ensure user friendliness, it is required
that communication should be possible even if the
distance between the reader/writer 11 and the antenna of
the transponder 12 is 10 cm or longer.
[0007]
5 If the distance between the reader/writer 11 and
the transponder 12 becomes longer, the degree of
modulation of a load-modulated carrier signal becomes
lower, and detection of response information becomes
difficult as described above. To compensate for that,
10 the peak-to-peak voltage (hereinafter referred to as Vpp)
of the carrier signal is increased to approximately 20 V.
[0008]
Fig. 3 shows an example structure of a conventional
reader/writer that can be used in a case where Vpp of the
15 carrier signal is 20 V. This reader/writer 20 detects
response information based on amplitude changes in the
voltage of a load-modulated carrier signal.
[0009]
In the reader/writer 20, full-wave rectification is
20 performed on the load-modulated carrier signal, and
envelope detection is performed on the carrier signal by
a peak holding circuit that outputs a detection signal.
For example, in the case of a carrier signal loadmodulated
to a modulation degree of 10% as shown in A of
25 Fig. 4, full-wave rectification is performed as shown in
B of Fig. 4, and a detection signal with a 1 V difference
is output as shown in C of Fig. 4.
CITATION LIST
30 PATENT DOCUMENT
[00101
Patent Document 1: JP 2001-307031 A
SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
5 [0011]
As described above, the conventional reader/writer
20 detects response information as amplitude changes in
the voltage of a carrier signal. Therefore, when the
degree of modulation of the carrier signal becomes lower,
10 response information cannot be accurately detected.
[0012]
Meanwhile, it is known that, in a case where a
carrier signal is load-modulated based on response
information at the transponder, the load modulation not
15 only causes amplitude changes in the voltage of the
carrier signal, but also causes changes in the phase of
the voltage. With the characteristics being taken
advantage of, an IQ detector (a quadrature detector) that
can detect both amplitude changes and phase changes in
20 voltage is used in the reader/writer.
[0013]
A conventional IQ detector is often used in a 50 $2
system that processes high-frequency signals, and the
highest allowable Vpp of input carrier signals is as low
25 as 2 V in most conventional IQ detectors.
[0014]
As described above, Vpp of carrier signals is set
at approximately 20 V. Therefore, to use a conventional
IQ detector in the reader/writer, an attenuator that
30 attenuates Vpp of a carrier signal to 1/10 of the
original value is provided in the stage before the
conventional IQ detector, for example, as shown in Fig. 5.
In this case, a carrier signal having Vpp attenuated by
the attenuator has an amplitude difference of 0.1 V in
the voltage, and only a difference of 0.1 V is caused in
5 the detection signal to be output from the IQ detector,
as shown in Fig. 6. As a result, the detection
sensitivity of the reader/writer 30 to response
information might become lower.
[0015]
10 This disclosure is being made in view of those
circumstances, and an object thereof is to detect
response information with high accuracy from a carrier
signal that is load-modulated based on the response
information.
SOLUTIONS TO PROBLEMS
A signal processing device as a first aspect of
this disclosure includes: a positive detecting unit that
20 detects a positive amplitude fluctuation portion of the
voltage of a load-modulated carrier signal; a negative
detecting unit that detects a negative amplitude
fluctuation portion of the voltage of the carrier signal;
and a combining unit that combines the positive amplitude
25 fluctuation portion and the negative amplitude
fluctuation portion of the voltage of the carrier signal.
[0017]
The positive detecting unit may include a first
generating unit that generates a positive threshold of
30 the voltage of the carrier signal, and a first selecting
unit that compares the voltage of the carrier signal with
the positive threshold, and selects the value of the
larger one. The negative detecting unit may include a
second generating unit that generates a negative
threshold of the voltage of the carrier signal, and a
5 second selecting unit that compares the voltage of the
carrier signal with the negative threshold, and selects
the value of the smaller one.
[0018]
The signal processing device as the first aspect of
10 this disclosure may further include a shaping unit that
shapes the waveform of the result of the combining of the
positive amplitude fluctuation portion and the negative
amplitude fluctuation portion into a sinusoidal wave.
[0019]
15 A signal processing method as the first aspect of
this disclosure is a signal processing method for a
signal processing device that attenuates the voltage of a
load-modulated carrier signal. The signal processing
method includes: a positive detecting step of detecting a
20 positive amplitude fluctuation portion of the voltage of
the carrier signal; a negative detecting step of
detecting a negative amplitude fluctuation portion of the
voltage of the carrier signal; and a combining step of
combining the positive amplitude fluctuation portion and
25 the negative amplitude fluctuation portion of the voltage
of the carrier signal, the steps being carried out by the
signal processing device.
[0020]
In the first aspect of this disclosure, a positive
30 amplitude fluctuation portion of the voltage of a carrier
signal is detected, a negative amplitude fluctuation
portion of the voltage of the carrier signal is detected,
and the positive amplitude fluctuation portion and the
negative amplitude fluctuation portion of the voltage of
the carrier signal are combined.
5 [0021]
A receiving device as a second aspect of this
disclosure includes: a receiving unit that receives a
load-modulated carrier signal; a positive detecting unit
that detects a positive amplitude fluctuation portion of
10 the voltage of the load-modulated carrier signal; a
negative detecting unit that detects a negative amplitude
fluctuation portion of the voltage of the carrier signal;
a combining unit that combines the positive amplitude
fluctuation portion and the negative amplitude
15 fluctuation portion of the voltage of the carrier signal;
and a detecting unit that detects the result of the
combining of the positive amplitude fluctuation portion
and the negative amplitude fluctuation portion.
[0022]
20 The receiving device as the second aspect of this
disclosure may further include a shaping unit that shapes
the waveform of the result of the combining of the
positive amplitude fluctuation portion and the negative
amplitude fluctuation portion into a sinusoidal wave. In
25 this receiving device, the detecting unit may detect the
result of the combining shaped into a sinusoidal wave.
100231
In the second aspect of this disclosure, a loadmodulated
carrier signal is received, a positive
30 amplitude fluctuation portion of the voltage of the
carrier signal is detected, a negative amplitude
fluctuation portion of the voltage of the carrier signal
is detected, the positive amplitude fluctuation portion
and the negative amplitude fluctuation portion are
combined, and the result of the combining is detected.
5
EFFECTS OF THE INVENTION
[0024]
According to the first aspect of this disclosure,
the degree of modulation of amplitude changes of a
10 carrier signal that is load-modulated based on response
information can be increased.
[0025]
According to the second aspect of this disclosure,
response information can be detected with high accuracy
15 from a received carrier signal that is load-modulated
based on the response information.
BRIEF DESCRIPTION OF DRAWINGS
[0026]
20 Fig. 1 is a circuit diagram showing an example
structure of a conventional non-contact communication
system.
Fig. 2 is a diagram for explaining changes in the
degree of modulation of a load-modulated carrier signal.
25 Fig. 3 is a circuit diagram showing an example
structure of a conventional reader/writer that detects
amplitude changes in the voltage of a load-modulated
carrier signal.
Fig. 4 is a diagram showing a detection signal to
30 be output from the reader/writer shown in Fig. 3.
Fig. 5 is a circuit diagram showing an example
structure of a reader/writer including an attenuator and
a conventional IQ detector.
Fig. 6 is a diagram showing amplitude changes in
the voltage of an attenuated carrier signal that is input
5 to the IQdete ctor in the reader/writer shown in Fig. 5.
Fig. 7 is a diagram for comparing a case where Vpp
of a carrier signal is attenuated by the conventional
attenuator shown in Fig. 5 with a case where Vpp of a
carrier signal is attenuated by a modulation adjusting
10 unit of this disclosure.
Fig. 8 is a diagram illustrating a technique
attenuating Vpp without a decrease in the degree of
modulation of the carrier signal.
Fig. 9 is a block diagram showing an example
15 structure of a reader/writer as an embodiment.
Fig. 10 is a block diagram showing an example
structure of the modulation adjusting unit.
Fig. 11 is a block diagram showing a first example
structure of an electronic circuit that realizes the
20 modulation adjusting unit.
Fig. 12 is a diagram showing a load-modulated
carrier signal that is input to the first example
structure of the modulation adjusting unit.
Fig. 13 is a diagram showing the signal waveforms
25 at respective parts of the first example structure of the
modulation adjusting unit.
Fig. 14 is a diagram showing the Vpp reduction
effect achieved by the first example structure of the
modulation adjusting unit.
30 Fig. 15 is a diagram showing a definition of a
degree of modulation.
Fig. 16 is a flowchart for explaining a signal
detecting operation to be performed by the reader/writer.
Fig. 17 is a block diagram showing a second example
structure of an electronic circuit that realizes the
5 modulation adjusting unit.
Fig. 18 is a diagram showing a load-modulated
carrier signal that is input to the second example
structure of the modulation adjusting unit.
Fig. 19 is a diagram showing the signal waveforms
10 at respective parts of the second example structure of
the modulation adjusting unit.
Fig. 20 is a diagram showing the Vpp reduction
effect achieved by the second example structure of the
modulation adjusting unit.
15 Fig. 21 is a diagram showing waveforms output from
the modulation adjusting unit.
Fig. 22 is a block diagram showing another example
structure of the reader/writer.
20 MODES FOR CARRYING OUT THE INVENTION
[0027]
The following is a detailed description of best
modes (hereinafter referred to as embodiments) for
carrying out the invention, with reference to the
25 drawings.
[0028]

First, the outline of this disclosure is described.
Fig. 7 shows the difference between a case where Vpp of a
30 carrier signal that is load-modulated based on response
information is attenuated by the conventional attenuator
shown in Fig. 5 (A in the drawing), and a case where Vpp
of a carrier signal that is load-modulated based on
response information is attenuated by a modulation
adjusting unit 52 (Fig. 9) of this disclosure (B in the
5 drawing).
[0029]
In the case where Vpp of a load-modulated carrier
signal is attenuated by the conventional attenuator, the
amplitude of the voltage is compressed overall as shown
10 in A in the drawing. As a result, the amplitude change
caused by response information or the degree of
modulation of the carrier signal is reduced, and the
accuracy of response information detection becomes lower.
In view of this, this disclosure suggests a technique for
15 attenuating Vpp of a carrier signal without a decrease in
the degree of modulation of the carrier signal as shown
in B in the drawing.
[0030]
Fig. 8 specifically illustrates this technique.
20 The midpoint potential portion that is not affected by
response information is removed from a pre-attenuation
load-modulated carrier signal shown in A in the drawing,
and a positive amplitude fluctuation portion and a
negative amplitude fluctuation portion that are the
25 amplitude change components of the voltage affected by
response information are detected, as shown in B in the
drawing. Further, the positive amplitude fluctuation
portion and the negative amplitude fluctuation portion
that are affected by response information are added to
30 each other, as shown in C in the drawing.
[0031]
In this manner, a carrier signal that has Vpp
attenuated but maintains the amplitude change components
to be affected by response information (with the degree
of modulation relatively increased) can be obtained.
5 Accordingly, response information can be detected with a
higher degree of accuracy by detecting this attenuated
carrier signal.
[0032]

10 [Example Structure of a Reader/Writerl
Fig. 9 shows an example structure of a
reader/writer as an embodiment in this disclosure.
[0033]
This reader/writer 50 is used in a non-contact
15 communication system as shown in Fig. 1, for example.
The reader/writer 50 receives a high-voltage
(approximately 20 V) carrier signal that is loadmodulated
in accordance with response information at the
transponder, performs quadrature detection, and detects
20 the response information as a result of the detection.
[0034]
The reader/writer 50 includes an antenna 51, a
modulation adjusting unit 52, and an IQ detecting unit 53.
[0035]
25 The antenna 51 receives a load-modulated carrier
signal, and outputs the carrier signal to the modulation
adjusting unit 52. The modulation adjusting unit 52
attenuates Vpp of the load-modulated carrier signal, and
outputs the carrier signal to the IQ detecting unit 53,
30 while maintaining the amplitude change components of the
load-modulated carrier signal, as shown in Fig. 8. The
IQ detecting unit 53 performs quadrature detection (IQ
detection) on the carrier signal input from the
modulation adjusting unit 52, and detects response
information as a result of the detection.
5 [0036]
[Example Structure of the Modulation Adjusting Unit
52 I
Fig. 10 shows an example structure of the
modulation adjusting unit 52. The modulation adjusting
10 unit 52 includes a positive DC generating unit 61, a
positive selecting unit 62, a negative DC generating unit
63, a negative selecting unit 64, and an adding unit 65.
[0037]
Based on a load-modulated carrier signal that is
15 input from the antenna 51, the positive DC generating
unit 61 generates a positive threshold that is the
positive DC component (a fixed value) of the voltage of
the load-modulated carrier signal, and outputs the
positive threshold to the positive selecting unit 62.
20 Specifically, the positive threshold for extracting the
waveform shown in the upper portion of B in Fig. 8 is
generated from the load-modulated carrier signal shown in
A in Fig. 8, for example.
[0038]
25 The positive selecting unit 62 compares the voltage
of the load-modulated carrier signal input from the
antenna 51 with the value of the positive DC component
(the positive threshold) input from the positive DC
generating unit 61, and outputs the larger value to the
30 adding unit 65. As a result of this selection, the
positive amplitude fluctuation portion of the voltage of
the carrier signal is extracted as shown in the upper
portion of B of Fig. 8, for example.
[0039]
Based on the load-modulated carrier signal that is
5 input from the antenna 51, the negative DC generating
unit 63 generates a negative threshold that is the
negative DC component (a fixed value) of the voltage of
the load-modulated carrier signal, and outputs the
negative threshold to the negative selecting unit 64.
10 Specifically, the negative threshold for extracting the
waveform shown in the lower portion of B in Fig. 8 is
generated from the load-modulated carrier signal shown in
A in Fig. 8, for example.
[0040]
15 The negative selecting unit 64 compares the voltage
of the load-modulated carrier signal input from the
antenna 51 with the value of the negative DC component
(the negative threshold) input from the negative DC
generating unit 62, and outputs the smaller value to the
20 adding unit 65. As a result of this selection, the
negative amplitude fluctuation portion of the voltage of
the carrier signal is extracted as shown in the lower
portion of B of Fig. 8, for example.
[0041]
25 The adding unit 65 adds the output of the positive
selecting unit 62 and the output of the negative
selecting unit 64, and outputs the addition result (Fig.
12c) to the IQ detecting unit 53. As the addition result,
a signal that has a lower Vpp than that of the original
30 carrier signal and maintains the fluctuation portions of
the voltage is obtained as shown in C in Fig. 8, for
example.
[0042]
[First Example Structure of an Electronic Circuit
that Realizes the Modulation Adjusting Unit 521
5 Fig. 11 shows a first example structure of an
electronic circuit that realizes the modulation adjusting
unit 52. It should be noted that the components
equivalent to those in Fig. 10 are denoted by the same
reference numerals as those used in Fig. 10.
10 [0043]
In Fig. 11, the positive DC generating unit 61 is
formed with a diode D11, a resistor R11, and a capacitor
C11. The diode Dl1 passes only the positive voltage of a
carrier signal that is input from the antenna 51
15 connected to the anode side. Accordingly, a positive
voltage is applied to the capacitor C11. The resistor
R11 prevents excess current from flowing into the
capacitor C11. Accordingly, the value of the voltage
accumulated in the capacitor C11 can be adjusted by
20 changing the value of the resistor R11.
[0044]
The positive selecting unit 62 is formed with a
diode Dl2 and a diode Dl3 that are connected in parallel.
The positive voltage from the capacitor C11 connected to
25 the anode side is applied to the diode D12. The positive
voltage of the carrier signal from antenna 51 connected
to the anode side is applied to the diode D13. As a
result, the positive voltage accumulated in the capacitor
C11 or the positive voltage of the carrier signal,
30 whichever is higher, is output to the adding unit 65 of a
later stage.
[ 0 0 4 5 1
The negative DC generating unit 63 is formed with a
diode D21, a resistor R21, and a capacitor C21. The
diode D21 passes only the negative voltage of the carrier
5 signal that is input from the antenna 51 connected to the
cathode side. Accordingly, a negative voltage is applied
to the capacitor C21. The resistor R21 prevents excess
current from flowing into the capacitor C21. Accordingly,
the value of the voltage accumulated in the capacitor C21
10 can be adjusted by changing the value of the resistor R21.
[0046]
The negative selecting unit 64 is formed with a
diode D22 and a diode D23 that are connected in parallel.
The negative voltage from the capacitor C21 connected to
15 the cathode side is applied to the diode D22. The
negative voltage of the carrier signal from antenna 51
connected to the cathode side is applied to the diode D23.
As a result, the negative voltage accumulated in the
capacitor C21 or the negative voltage of the carrier
20 signal, whichever is lower, is output to the adding unit
65 of a later stage.
[0047]
The adding unit 65 is formed with a resistor R12
and a resistor R22.
25 [0048]
When a load-modulated carrier signal having Vpp =
40 V as shown in Fig. 12 is input to the first example
structure of the modulation adjusting unit 52 shown in
Fig. 11, the positive DC generating unit 61 can obtain a
30 positive fixed value (a threshold) as shown in Fig. 13b.
The positive threshold can be adjusted by changing the
value of the resistor R11. The positive selecting unit
62 extracts the higher portion than the positive
threshold shown in Fig. 13b from the carrier signal, and
obtains a signal having the waveform shown in Fig. 13a.
5 [0049]
Meanwhile, the negative DC generating unit 63 can
obtain a negative fixed value (a threshold) as shown in
Fig. 13d. The negative threshold can be adjusted by
changing the value of the resistor R21. The negative
10 selecting unit 64 extracts the lower portion than the
negative threshold shown in Fig. 13d from the carrier
signal, and obtains a signal having the waveform shown in
Fig. 13e.
[0050]
15 The adding unit 65 adds the waveform shown in Fig.
13a and the waveform shown in Fig. 13e, to obtain a
signal having the waveform shown in Fig. 13c. The signal
is output to a later stage.
[0051]
20 Fig. 14 shows the waveform of the voltage of the
carrier signal that is shown in Fig. 12 and is input to
the first example structure of the modulation adjusting
unit 52, and the waveform of the voltage that is shown in
Fig. 13c and is output from the adding unit 65, with the
25 widths of the waveforms being adjusted. Specifically,
the ordinate axis in A in Fig. 14 indicates the f20 V
range, and the ordinate axis in B in Fig. 14 indicates
the f2 V range. Fig. 15 shows a definition of a degree
of modulation of a load-modulated signal. A degree of
30 modulation is calculated by (A - B)/(A + B), which uses
the maximum Vpp A and the minimum Vpp B.
[0052]
As is apparent from Fig. 14, the maximum Vpp A of
the carrier signal input to the first example structure
of the modulation adjusting unit 52 is 40 V, and the
5 minimum Vpp B is 36 V. Accordingly, the degree of
modulation is 5.3%. On the other hand, the maximum Vpp A
of the signal output from the adding unit 65 is 3.42 V,
and the minimum Vpp B is 1.46 V. Accordingly, the degree
of modulation is 40.2%.
10 [0053]
With the first example structure of the modulation
adjusting unit 52 shown in Fig. 11, the degree of
modulation can be made approximately 7.5 times higher,
while Vpp of the carrier signal is reduced. Thus, a
15 quadrature detection LSI having 2 V as the highest
allowable Vpp can be used in the IQ detecting unit 53,
and furthermore, detection based on amplitude changes in
the voltage of the carrier signal can be performed.
[0054]
20 [Operation by the Reader/Writer 501
Fig. 16 is a flowchart for explaining a signal
detecting operation to be performed by the reader/writer
50.
[00551
25 This signal detecting operation is performs on the
assumption that a carrier signal load-modulated by the
transponder is received by the antenna 51 of the
reader/writer 50, and is input to the modulation
adjusting unit 52.
30 [0056]
In step S1, the positive DC generating unit 61 of
the modulation adjusting unit 52 generates a positive
threshold based on the carrier signal input from the
antenna 51, and outputs the positive threshold to the
positive selecting unit 62. In step S2, the positive
5 selecting unit 62 compares the voltage of the carrier
signal input from the antenna 51 with the positive
threshold from the positive DC generating unit 61, and
outputs the value of the larger one to the adding unit 65.
[0057]
10 In step S3, the negative DC generating unit 63
generates a negative threshold based on the carrier
signal input from the antenna 51, and outputs the
negative threshold to the negative selecting unit 64. In
step S4, the negative selecting unit 64 compares the
15 voltage of the carrier signal input from the antenna 51
with the negative threshold input from the negative DC
generating unit 62, and outputs the value of the smaller
one to the adding unit 65.
[0058]
20 The procedures of steps S1 through S4 are
simultaneously carried out in practice.
[0059]
In step S5, the adding unit 65 adds the output of
the positive selecting unit 62 and the output of the
25 negative selecting unit 64, and outputs the addition
result (Fig. 12c) to the IQ detecting unit 53. In step
S6, the IQ detecting unit 53 performs IQ detection on the
signal that is input from the adding unit 65, has a lower
Vpp than that of the original carrier signal, and
30 maintains the fluctuation portions of voltage. As a
result of the IQ detection, response information from the
transponder can be obtained. The signal detecting
operation is thus completed.
[0060]
[Second Example Structure of an Electronic Circuit
5 that Realizes the Modulation Adjusting Unit 521
Fig. 17 shows a second example structure of an
electronic circuit that realizes the modulation adjusting
unit 52. The same components as those of the first
example structure shown in Fig. 11 are denoted by the
10 same reference numerals and characters as those used in
Fig. 11, and therefore, explanation of them will not be
repeated.
[0061]
The second example structure differs from the first
15 example structure in the structure of the adding unit 65.
Specifically, the adding unit 65 is formed with the
resistor R12 and the resistor R22 in the first example
structure, but the second example structure further
includes a resistor R31 and an operational amplifier 71.
20 [0062]
The resistor R31 has a smaller resistance value
than that of the resistor R12 and the resistor R22, and
functions as a feedback resistance for the operational
amplifier 71. The operational amplifier 71 attenuates
25 the sum of the output of the positive selecting unit 62
that is input via the resistor R12, and the output of the
negative selecting unit 64 that is input via the resistor
R22. The attenuated value is output to a later stage.
[0063]
30 When a load-modulated carrier signal having Vpp =
40 V as shown in Fig. 18 is input to the second example
structure of the modulation adjusting unit 52 shown in
Fig. 17, the positive DC generating unit 61 can obtain a
positive fixed value (a positive threshold) as shown in
Fig. 19b. The positive threshold can be adjusted by
5 changing the value of the resistor R11. The positive
selecting unit 62 extracts the portion exceeding the
positive threshold shown in Fig. 19b from the carrier
signal, and obtains a signal having the waveform shown in
Fig. 19a.
10 [0064]
Meanwhile, the negative DC generating unit 63 can
obtain a negative fixed value (a negative threshold) as
shown in Fig. 19d. The negative threshold can be
adjusted by changing the value of the resistor R21. The
15 negative selecting unit 64 extracts the portion lower
than the negative threshold shown in Fig. 19d from the
carrier signal, and obtains a signal having the waveform
shown in Fig. 19e.
[0065]
20 The adding unit 65 adds the waveform shown in Fig.
19a and the waveform shown in Fig. 19e, to obtain a
signal having the waveform shown in Fig. 19c. The signal
is output to a later stage.
[0066]
25 Fig. 20 shows the waveform of the voltage of the
carrier signal that is shown in Fig. 18 and is input to
the second example structure of the modulation adjusting
unit 52, and the waveform of the voltage that is shown in
Fig. 19c and is output from the adding unit 65, with the
30 widths of the waveforms being adjusted. Specifically,
the ordinate axis in A in Fig. 20 indicates the f20 V
range, and the ordinate axis in B in Fig. 20 indicates
the f2 V range.
[0067]
As is apparent from Fig. 20, the maximum Vpp A of
5 the carrier signal input to the second example structure
of the modulation adjusting unit 52 is 40 V, and the
minimum Vpp B is 36 V. Accordingly, the degree of
modulation is 5.3%. On the other hand, the maximum Vpp A
of the signal output from the adding unit 65 is 3.11 V,
10 and the minimum Vpp B is 2.13 V. Accordingly, the degree
of modulation is 18.7%.
[0068]
With the second example structure of the modulation
adjusting unit 52 shown in Fig. 17, the degree of
15 modulation can be made approximately 3.5 times higher,
while Vpp of the carrier signal is reduced. Thus, a
quadrature detection LSI having 2 V as the highest
allowable Vpp can be used in the IQ detecting unit 53,
and furthermore, detection based on amplitude changes in
20 the voltage of the carrier signal can be performed.
[0069]
[Another Example Structure of the Reader/Writer]
The voltage of a carrier signal attenuated by the
above described modulation adjusting unit 52 has the
25 waveform shown in A of Fig. 21. This carrier signal may
be input to the IQ detecting unit 53, and is subjected to
detection. However, detection accuracy can be further
increased, if the waveform is shaped into a waveform
similar to a sinusoidal wave as shown in B of Fig. 21.
30 [0070]
Fig. 22 shows an example structure of a
reader/writer 80 that can shape the waveform of the
attenuated carrier signal into a waveform similar to a
sinusoidal wave as described above, and input the carrier
signal with the shaped waveform to the IQ detecting unit
The reader/writer 80 is the same as the
reader/writer 50 shown in Fig. 9, except that a LPF 81 is
provided between the modulation adjusting unit 52 and the
10 IQdete cting unit 53. Other than the LPF 81, the
components are the same as those of the reader/writer 50.
The LPF 81 can make the waveform of the attenuated
carrier signal similar to a sinusoidal wave by removing
the high-frequency components of the attenuated carrier
15 signal.
[0072]
With the reader/writer 80, response information can
be detected with a higher degree of accuracy than that
with the reader/writer 50.
20 [0073]
Having the modulation adjusting unit 52, each of
the above described readers/writers 50 and 80 is very
effective in detecting amplitude fluctuations in the
voltage of a carrier signal. In a case where the
25 distance between the reader/writer and the transponder is
relatively long, load modulation is more often detected
as an amplitude change than as a phase change. Therefore,
this disclosure is particularly effective in extending
the communication distance between the reader/writer and
30 the transponder.
[0074]
The modulation adjusting unit 52 of this disclosure
can be used not only in the reader/writer of a noncontact
communication system, but also in a receiving
device that receives load-modulated signals.
5 [0075]
In this specification, a "system" means an entire
apparatus formed with more than one device.
LO0761
It should be noted that embodiments of this
10 disclosure are not limited to the above described
embodiments, and various modifications may be made to
them without departing from the scope of this disclosure.
REFERENCE SIGNS LIST
15 [00771
50 Reader/writer, 51 Antenna, 52 Modulation
adjusting unit, 53 IQ detecting unit, 61 Positive DC
generating unit, 62 Positive selecting unit, 63 Negative
DC generating unit, 64 Negative selecting unit, 65 Adding
20 unit, 80 Reader/writer, 81 LPF

claims:
The carrier signal with a positive threshold value, and
detectingthe largerone ofthevalues as apositive amplitude
fluctuation portion;
a negative detecting step o.f comparing the voltage of
5 the carrier signal with a negative threshold value, and
detectingthesmalleroneofthevaluesasanegativeamplitude
fluctuation portion; and ,
. a combining step of combining the positive amplitude
fluctuation portion and the negative amplitude fluctuation
portion the the carrier
the steps being carried out by the signal processing
device.
4.
15 A receiving device comprising:
areceivingunitconfig~redtoreceiveanASK-modulated
carrier signal;
apositivedetectingunit configured to compare avoltage
of the carrier signal with a positive threshold value, and
20 detect the larger one of the values as a positive amplitude
fluctuation portion;
a negative detecting unit configured to compare the
voltageofthecarriersignalwithanegativethresholdvalue,
and detect the smaller one of the vaiues as a negative amplitude
25 fluctuation portion;
a combining unit configured to combine the positive
amplitude fluctuation portion and the negative amplitude
fluctuationportion ofthe voltage ofthe carrier signal; and
a detecting unit configured to detect a result of the
', 30 combining of the positive amplitude fluctuation portion and
the negative amplitude fluctuation portion.
5. The receiving device according to claim 9, further
comprising:
a shaping unit configured to shape the waveform of the
5 result ofthe combiningofthepositive amplitude fluctuation
portion and the negative amplitude fluctuation portion into
a sinusoidal wave,
wherein the detecting unit detects the result of the
shaped into the sinusoidal wave.
Dated this 1 4m day of August, 201 3
~SHRIMANTS ~ G H J
OF REMFRY & SAGAR
ATTORNEY FOR THE APPLICANT[S]