U.S. patent application number 16/103946 was filed with the patent office on 2019-06-13 for rf tag circuit.
This patent application is currently assigned to OMRON Corporation. The applicant listed for this patent is OMRON Corporation. Invention is credited to Tetsuya NOSAKA, Satoshi YASE.
Application Number | 20190180157 16/103946 |
Document ID | / |
Family ID | 63311802 |
Filed Date | 2019-06-13 |
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United States Patent
Application |
20190180157 |
Kind Code |
A1 |
YASE; Satoshi ; et
al. |
June 13, 2019 |
RF TAG CIRCUIT
Abstract
An RF tag circuit including a power storage unit is provided, in
which an increase in time required for a voltage change occurring
when an impedance is adjusted is reduced. The RF tag circuit is
connected to an antenna and a load. The RF tag circuit includes a
rectification circuit, a matching circuit, a power storage unit,
and a control unit. The rectification circuit rectifies a radio
wave received by the antenna and supplies DC power. The matching
circuit, of which an impedance is changeable, is interposed between
the antenna and the rectification circuit. The power storage unit
stores DC power input from the rectification circuit and supplies
the stored DC power to the load. The control unit disconnects the
power storage unit from the RF tag circuit and adjusts the
impedance of the matching circuit such that the amount of the power
supplied by the rectification circuit increases.
Inventors: |
YASE; Satoshi; (Nara-shi,
JP) ; NOSAKA; Tetsuya; (OSAKA, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OMRON Corporation |
KYOTO |
|
JP |
|
|
Assignee: |
OMRON Corporation
KYOTO
JP
|
Family ID: |
63311802 |
Appl. No.: |
16/103946 |
Filed: |
August 15, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06K 19/0723 20130101;
G06K 19/0702 20130101; H03H 7/38 20130101; G06K 19/0709 20130101;
H02M 7/06 20130101; G06K 19/0712 20130101; H03H 7/40 20130101; H02J
50/20 20160201; G06K 19/0716 20130101 |
International
Class: |
G06K 19/07 20060101
G06K019/07; H03H 7/38 20060101 H03H007/38; H02J 50/20 20060101
H02J050/20 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 14, 2017 |
JP |
2017-177014 |
Claims
1. An RF tag circuit connected to an antenna and a load, the RF tag
circuit comprising: a rectification circuit that rectifies a radio
wave received by the antenna and supplies DC power; a matching
circuit, of which an impedance is changeable, disposed between the
antenna and the rectification circuit; a power storage unit that
stores the DC power input from the rectification circuit and
supplies the stored DC power to the load; and a control unit that
disconnects the power storage unit from the RF tag circuit and
adjusts the impedance of the matching circuit such that the DC
power supplied by the rectification circuit increases.
2. The RF tag circuit according to claim 1, wherein when adjusting
the impedance of the matching circuit, the control unit further
executes a process of disconnecting the load from the RF tag
circuit and connecting a substitute load having a resistance value
different from the load to the RF tag circuit.
3. The RF tag circuit according to claim 2, wherein the substitute
load has a power consumption lower than the load or has a
resistance value larger than the load.
4. The RF tag circuit according to claim 2, wherein the load is
driven at a predetermined cycle, and wherein the substitute load
has a resistance value determined based on a duty ratio
representing a ratio of a driving period of the load in the
predetermined cycle and the resistance value of the load.
5. The RF tag circuit according to claim 4, wherein the substitute
load is a variable resistor of which a resistance value is
changeable, and wherein the control unit calculates a resistance
value based on a current consumption of the load, the duty ratio of
the load, and a voltage applied to the load, and sets the
calculated resistance value as the resistance value of the
substitute load.
6. The RF tag circuit according to claim 5, further comprising: a
measurement unit that measures a current supplied to the load,
wherein the current consumption of the load is measured by the
measurement unit.
7. The RF tag circuit according to claim 4, wherein the control
unit calculates the duty ratio of the load by aggregating a period
during which the load is driven and a period during which the load
is not driven.
8. The RF tag circuit according to claim 2, wherein the control
unit further executes a process of connecting the power storage
unit and the load when executing the process of connecting the
substitute load to the RF tag circuit.
9. The RF tag circuit according to claim 3, wherein the load is
driven at a predetermined cycle, and wherein the substitute load
has a resistance value determined based on a duty ratio
representing a ratio of a driving period of the load in the
predetermined cycle and the resistance value of the load.
10. The RF tag circuit according to claim 9, wherein the substitute
load is a variable resistor of which a resistance value is
changeable, and wherein the control unit calculates a resistance
value based on a current consumption of the load, the duty ratio of
the load, and a voltage applied to the load, and sets the
calculated resistance value as the resistance value of the
substitute load.
11. The RF tag circuit according to claim 10, further comprising: a
measurement unit that measures a current supplied to the load,
wherein the current consumption of the load is measured by the
measurement unit.
12. The RF tag circuit according to claim 5, wherein the control
unit calculates the duty ratio of the load by aggregating a period
during which the load is driven and a period during which the load
is not driven.
13. The RF tag circuit according to claim 6, wherein the control
unit calculates the duty ratio of the load by aggregating a period
during which the load is driven and a period during which the load
is not driven.
14. The RF tag circuit according to claim 9, wherein the control
unit calculates the duty ratio of the load by aggregating a period
during which the load is driven and a period during which the load
is not driven.
15. The RF tag circuit according to claim 10, wherein the control
unit calculates the duty ratio of the load by aggregating a period
during which the load is driven and a period during which the load
is not driven.
16. The RF tag circuit according to claim 3, wherein the control
unit further executes a process of connecting the power storage
unit and the load when executing the process of connecting the
substitute load to the RF tag circuit.
17. The RF tag circuit according to claim 4, wherein the control
unit further executes a process of connecting the power storage
unit and the load when executing the process of connecting the
substitute load to the RF tag circuit.
18. The RF tag circuit according to claim 5, wherein the control
unit further executes a process of connecting the power storage
unit and the load when executing the process of connecting the
substitute load to the RF tag circuit.
19. The RF tag circuit according to claim 6, wherein the control
unit further executes a process of connecting the power storage
unit and the load when executing the process of connecting the
substitute load to the RF tag circuit.
20. The RF tag circuit according to claim 7, wherein the control
unit further executes a process of connecting the power storage
unit and the load when executing the process of connecting the
substitute load to the RF tag circuit.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority benefit of Japan
application serial no. 2017-177014, filed on Sep. 14, 2017. The
entirety of the above-mentioned patent application is hereby
incorporated by reference herein and made a part of this
specification.
BACKGROUND
Technical Field
[0002] The disclosure relates to an RF tag circuit that is
connected to an antenna and a load.
Description of Related Art
[0003] In recent years, the development of RF tags has been
remarkable, and use of RF tags for driving loads such as a sensor,
an LED, an IC, a microcomputer, a communication circuit, and an RF
tag circuit as examples using power supplied through received radio
waves as an energy source has increased in addition to their
original use of object identification. In some cases, the electric
power received by RF tags is further increased such that the
electric power is stably supplied for operations of such loads. In
such an RF tag circuit, there are cases in which a power supply
capability for a load decreases due to impedance mismatch between
an antenna and the RF tag circuit. The impedance mismatch may occur
due to a change in the impedance of the antenna, for example,
according to the attachment or approach of a metal piece, or
dielectrics such as water or oil to the antenna. For this reason,
technologies for impedance matching between an antenna and an RF
tag circuit have been proposed. In impedance adjustment, a search
for an impedance value for which a voltage becomes a maximum is
performed while the impedance of the RF tag circuit is changed (for
example, see Japanese Patent Laid-Open No. 7-111470).
[0004] In order to stably drive a load even when the supplied
electric power decreases due to deterioration of the reception
status of radio waves or the like, an RF tag circuit including a
power storage unit such as a capacitor that stores electric power
supplied by radio waves is used. By using the electric power
supplied from the power storage unit, even when the electric power
supplied through radio waves decreases, a stable operation of the
load can be performed.
[0005] For a stable operation of the load, it is desirable that the
capacitance of the power storage unit is large. However, when the
capacitance of the power storage unit increases, the time constant
of the power storage unit increases. When the time constant is
large, a change in the voltage after a change of the impedance is
gentler than when the time constant is small. For this reason, a
time required for detecting a change in the voltage after a change
of the impedance may increase. In addition, a voltage change
occurring within a predetermined period during which the RF tag
circuit detects a voltage change may not reach a voltage range that
can be detected by the RF tag circuit, and the RF tag circuit may
erroneously detect that adjustment of the impedance has been
completed.
SUMMARY
[0006] An embodiment of the disclosure provides an RF tag circuit
connected to an antenna and a load as an example. The RF tag
circuit includes a rectification circuit, a matching circuit, a
power storage unit, and a control unit. The rectification circuit
rectifies a radio wave received by the antenna and supplies DC
power. The matching circuit, of which an impedance is changeable,
is disposed between the antenna and the rectification circuit. The
power storage unit stores DC power input from the rectification
circuit and supplies the stored DC power to the load. The control
unit disconnects the power storage unit from the RF tag circuit and
adjusts the impedance of the matching circuit such that the DC
power supplied by the rectification circuit increases.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a diagram illustrating one example of a
configuration and a use form of an RF tag circuit according to an
embodiment;
[0008] FIG. 2 is a diagram illustrating one example of the
configuration of a matching circuit;
[0009] FIG. 3 is a diagram illustrating one example of the
configuration of a variable resistor of a matching circuit;
[0010] FIG. 4 is a diagram illustrating one example of the
configuration of a rectification circuit;
[0011] FIG. 5 is a diagram illustrating one example of the
configuration of a load control circuit;
[0012] FIG. 6 is a diagram illustrating one example of the
configuration of an impedance adjustment control circuit;
[0013] FIG. 7 is a diagram illustrating one example of a control
flow of a control unit/storage unit controlling an impedance
adjustment control circuit;
[0014] FIG. 8 is a diagram illustrating one example of variations
in a power supply voltage input from a rectification circuit to an
impedance adjustment control circuit when an impedance of a
matching circuit is close to an appropriate value;
[0015] FIG. 9 is a diagram illustrating one example of a processing
flow according to an embodiment;
[0016] FIG. 10 is a diagram illustrating one example of a
processing flow of impedance adjustment according to an
embodiment;
[0017] FIG. 11 is a diagram illustrating one example of variations
in a power supply voltage input from a rectification circuit to an
impedance adjustment control circuit in an embodiment;
[0018] FIG. 12 is a diagram comparing a voltage drop according to
an embodiment with a voltage drop according to a first modified
example;
[0019] FIG. 13 is a diagram illustrating one example of the
configuration of an RF tag circuit according to the first modified
example;
[0020] FIG. 14 is a diagram illustrating one example of the
configuration of a load control circuit according to the first
modified example;
[0021] FIG. 15 is a diagram illustrating one example of a
processing flow according to the first modified example;
[0022] FIG. 16 is a diagram illustrating one example of variations
in a power supply voltage input from a rectification circuit to an
impedance adjustment control circuit in the first modified
example;
[0023] FIG. 17 is a diagram illustrating one example of the
configuration of an RF tag circuit according to a second modified
example;
[0024] FIG. 18 is a diagram illustrating one example of the
configuration of an RF tag circuit according to a third modified
example;
[0025] FIG. 19 is a diagram illustrating one example of the
configuration of a current measuring circuit;
[0026] FIG. 20 is a diagram illustrating one example of the
configuration of an RF tag circuit according to a fourth modified
example; and
[0027] FIG. 21 is a diagram illustrating one example of the
configuration of a load control circuit according to a fifth
modified example.
DESCRIPTION OF THE EMBODIMENTS
[0028] An embodiment of the disclosure is provided to reduce an
increase in a time required for a voltage change occurring when
impedance is adjusted in an RF tag circuit including a power
storage unit.
[0029] In the configuration described above, the power storage unit
is a device capable of storing electric power and is, for example,
a capacitor. The load is a device driven using electric power
supplied through a received radio wave as an energy source. The
load is, for example, a sensor, an LED, an IC, a microcomputer, a
communication circuit, an RF tag circuit, or the like. The matching
circuit includes a variable impedance device. The variable
impedance device may be, for example, a circuit acquired by
combining a plurality of capacitors or an analog control device
such as a varactor diode. In the configuration described above, the
load can be driven using electric power supplied from the power
storage unit. For this reason, even when the status of reception of
radio waves using the antenna deteriorates, the RF tag circuit can
stably drive the load. When the impedance is adjusted using the
control unit, the power storage unit is disconnected from the RF
tag circuit, and accordingly, an increase in time required for a
voltage change at the time of adjusting the impedance due to the
influence of the time constant of the power storage unit is
reduced.
[0030] In the configuration described above, when the impedance of
the matching circuit is adjusted, the control unit may further
execute a process of disconnecting the load from the RF tag circuit
and connecting a substitute load having a resistance value
different from the load to the RF tag circuit. Here, the substitute
load may have a power consumption lower than the load or have a
resistance value larger than the load. In addition, in the
configuration described above, the load may be driven at a
predetermined cycle, and the substitute load may have a resistance
value determined based on a duty ratio representing a ratio between
a driving period of the load in the predetermined cycle and the
resistance value of the load. By connecting such a substitute load,
the magnitude of a drop in a voltage in a period in which impedance
adjustment is performed by an adjustment unit decreases.
[0031] In the configuration described above, the substitute load
may be a variable resistor of which a resistance value is
changeable. In such a case, the control unit may calculate a
resistance value based on current consumption of the load, the duty
ratio of the load, and a voltage applied to the load and set the
calculated resistance value as a resistance value of the substitute
load. In addition, the resistance value of the substitute load may
be appropriately set by a user using the RF tag circuit. By
employing such a configuration, even when there are variations in
the current consumption of the load, the duty ratio of the load,
and the voltage applied to the load, an appropriate resistance
value can be set in the substitute load.
[0032] In the configuration described above, a measurement unit
that measures a current supplied to the load may be further
included, and the current consumption of the load may be measured
by the measurement unit. By employing such a configuration, even
when there are variations in the current consumption of the load,
an appropriate resistance value can be set in the substitute
load.
[0033] In the configuration described above, the control unit may
calculate the duty ratio of the load by aggregating a period during
which the load is driven and a period during which the load is not
driven. By employing such a configuration, even when there are
variations from a predetermined duty ratio, an appropriate
resistance value can be set in the substitute load.
[0034] In the configuration described above, the control unit may
further execute a process of connecting the power storage unit and
the load when executing the process of connecting the substitute
load to the RF tag circuit. By employing such a configuration, also
when the impedance is adjusted, electric power is supplied from the
power storage unit to the load. For this reason, even when the
impedance is adjusted, the load can be continuously operated.
[0035] An RF tag circuit of the disclosure is capable of reducing
an increase in a time required for a voltage change occurring when
impedance is adjusted in an RF tag circuit including a power
storage unit.
[0036] Hereinafter, embodiments will be described with reference to
the drawings. The configurations of the embodiments illustrated
below are examples, and the disclosed technologies are not limited
to the configurations of the embodiments.
First Embodiment
[0037] FIG. 1 is a diagram illustrating one example of a
configuration and a use form of an RF tag circuit 10 according to
an embodiment. The RF tag circuit 10 is connected to an antenna 20
and a normal load 30. The RF tag circuit 10 is a circuit that
constitutes a system in which a reader/writer device 40 can
wirelessly use the normal load 30. The normal load 30 is a device
that is driven using electric power supplied through received radio
waves as an energy source. The normal load 30 is, for example, a
sensor, an LED, an IC, a microcomputer, a communication circuit, an
RF tag circuit, or the like. The RF tag circuit 10 is a circuit
that drives the normal load 30 using radio waves received from the
reader/writer device 40 as an energy source. The RF tag circuit 10
may be regarded also as a wireless power supply circuit or a
wireless power supply device. In addition, the normal load 30
connected to the RF tag circuit 10 may be regarded as a wireless
sensor. The RF tag circuit 10 is, for example, realized by any one
of an IC chip, a circuit combining discrete components, and a
circuit combining an IC chip and discrete components. In addition,
the reader/writer device 40 is, for example, a device in which a
reader/writer 42 to which the antenna 41 is attached is connected
to a host device 43 such as a computer. The normal load 30 is one
example of a "load".
[0038] The RF tag circuit 10 is, for example, a circuit that is
connected to the antenna 20 receiving radio waves from the
reader/writer device 40 and the norinal load 30 used by the
reader/writer device 40. The RF tag circuit 10 includes a matching
circuit 11, a rectification circuit 12, a load control circuit 13,
an impedance adjustment control circuit 14, a control unit/storage
unit 15, and an adjustment trigger generating circuit 16.
[0039] The matching circuit 11 is a circuit that is used for
impedance matching between the antenna 20 and a circuit disposed
inside the RF tag circuit 10. A specific circuit configuration of
the matching circuit 11 is not particularly limited. The circuit
configuration of the matching circuit 11, for example, as
exemplified in FIG. 2, may be a circuit acquired by combining two
inductors 51 and 52 and a variable-capacitance capacitor 53 of
which a capacitance can be changed in accordance with an adjustment
signal supplied from the impedance adjustment control circuit 14.
As the variable-capacitance capacitor 53 of which a capacitance can
be changed in accordance with an adjustment signal received from
the impedance adjustment control circuit 14, for example, a circuit
acquired by combining capacitors C.sub.1 to C.sub.5 having mutually
different capacitance values and switches S.sub.C1 to S.sub.C5 as
illustrated in FIG. 3 may be used. In addition, the matching
circuit 11 may be an analog control device such as a varactor
diode. In the RF tag circuit 10, when a metal piece, or a
dielectric such as water or oil is attached to or approaches the
antenna 20, the impedance of the antenna 20 may change. When
impedance mismatch between the antenna 20 and the circuit disposed
inside the RF tag circuit 10 increases in accordance with a change
in the impedance of the circuit of the antenna 20, energy
transmission efficiency from the antenna 20 to the circuit disposed
inside the RF tag circuit 10 decreases. Thus, by achieving
impedance matching between the antenna 20 and the circuit disposed
inside the RF tag circuit 10 using the matching circuit 11, a
decrease in the energy transmission efficiency from the antenna 20
to the circuit disposed inside the RF tag circuit 10 is reduced.
The matching circuit 11 is one example of "matching circuit".
[0040] The rectification circuit 12 is a circuit that rectifies AC
power output by the antenna 20 that has received radio waves and
supplies DC power to the normal load 30 and each unit (the load
control circuit 13 and the impedance adjustment control circuit 14)
disposed inside the RF tag circuit 10. FIG. 4 is a diagram
illustrating one example of the configuration of the rectification
circuit 12. The rectification circuit 12, as exemplified in FIG. 4,
may be a circuit acquired by connecting voltage doubler
rectification circuits each configured of two diodes D (D.sub.1 and
D.sub.2 or the like) and two capacitors (C.sub.1 and C.sub.2 or the
like) in multiple stages. The rectification circuit 12 may generate
a DC signal of a separate system used for the impedance adjustment
separately from a power supply voltage VOUT used for driving the
normal load 30. The rectification circuit 12 is one example of a
"rectification circuit".
[0041] The load control circuit 13 is a circuit that activates the
normal load 30 in accordance with a signal received from the
control unit/storage unit 15. FIG. 5 is a diagram illustrating one
example of the configuration of the load control circuit 13. As the
load control circuit 13, as exemplified in FIG. 5, a circuit
including a switch (SW_LOAD) 131 switching on and off of the power
supply to the normal load 30, a capacitor 133, and a switch (SW_C)
132 switching on and off of the power supply to the capacitor 133
may be used. The SW_C 132 is normally in the on state, and the
capacitor 133, for example, stores DC power supplied from the
rectification circuit 12. The capacitor 133, for example, may store
excess power not used for driving the normal load 30 from the DC
power supplied from the rectification circuit 12. The excess power
is, for example, power supplied through a radio wave received by
the antenna in a period other than a period for driving the normal
load 30. The power stored in the capacitor 133 is supplied to the
normal load 30. By selecting the capacitor 133 of which a
capacitance is relatively large (for example, a capacitance larger
than a reciprocal of a resistance component of the normal load 30
(having a large time constant (in order of seconds))), a drop in
the voltage supplied to the normal load 30 can be reduced. By
selecting such a capacitor 133, even when instantaneous power
cutoff or the like occurs due to deterioration of the status of
reception from the reader/writer device 40 or the like, the normal
load 30 can be operated more stably. The SW_C 132 is turned off
when the load control circuit 13 receives a charge capacitance off
signal from the control unit/storage unit 15. When the SW_C 132 is
turned off, DC power supplied from the rectification circuit 12 is
supplied to the capacitor 133, and the capacitor 133 is charged.
The SW_LOAD 131 is turned on when the load control circuit 13
receives a load control signal ctrl from the control unit/storage
unit 15. When the SW_LOAD 131 is turned on, the DC power supplied
from the rectification circuit 12 is supplied to the normal load
30, and the normal load 30 is activated. As will be described
later, the load control signal ctrl is transmitted at a
predetermined cycle, and accordingly, the normal load 30 is
activated at the predetermined cycle. The capacitor 133 is one
example of a "power storage unit".
[0042] The control unit/storage unit 15 transmits a signal for
switching on and off of the SW_LOAD 131 and SW_C 132 of the load
control circuit 13. In addition, the control unit/storage unit 15
instructs the impedance adjustment control circuit 14 to start
impedance adjustment. The control unit/storage unit 15, for
example, transmits a load control signal ctrl to the load control
circuit 13 in response to a command (a clock signal or the like)
input from the outside at a predetermined cycle, thereby performing
switching on and off of the SW_LOAD 131 of the load control circuit
13. As a result, the normal load 30 is activated at the
predetermined cycle. When receiving an adjustment trigger from the
adjustment trigger generating circuit 16, the control unit/storage
unit 15 transmits an adjustment control signal instructing
impedance adjustment to the impedance adjustment control circuit 14
and transmits a charge capacitance off signal instructing to turn
off the SW_C 132 to the load control circuit 13.
[0043] The control unit/storage unit 15 is, for example, a device
acquired by combining a processor and a storage unit. The processor
is not limited to a single processor and may have a multi-processor
configuration. In addition, a single processor connected to a
single socket may have a multi-core configuration. At least a part
of the process executed by the processor, for example, may be
performed by a dedicated processor such as a digital signal
processor (DSP), a graphics processing unit (GPU), a numeric data
processor, a vector processor, or an image processing processor. In
addition, at least a part of the processor executed by the
processor may be executed by an integrated circuit (IC) or any
other digital circuit. An analog circuit may be included in at
least a part of the processor. The integrated circuit includes a
large scale integrated circuit (LSI), an application specific
integrated circuit (ASIC), and a programmable logic device (PLD).
The PLD, for example, includes a field-programmable gate array
(FPGA). The processor may be a combination of a processor and an
integrated circuit. This combination is, for example, called as a
micro controller unit (MCU), a system-on-chip (SoC), a system LSI,
a chip set, or the like. The storage unit is a storage medium for
which data can be read and written by the processor. The storage
unit is, for example, a storage medium that is directly accessed
from the processor. The storage unit, for example, includes a
random access memory (RAM) and a read only memory (ROM). The
control unit/storage unit 15 is one example of a "control
unit".
[0044] The adjustment trigger generating circuit 16 transmits an
adjustment trigger instructing to start impedance adjustment to the
control unit/storage unit 15. For example, when a DC voltage input
from the rectification circuit 12 to the impedance adjustment
control circuit 14 is lower than a predetermined threshold, the
adjustment trigger generating circuit 16 transmits an adjustment
trigger. For example, when a trigger is input from an external
circuit, the adjustment trigger generating circuit 16 may transmit
an adjustment trigger.
[0045] The impedance adjustment control circuit 14 is a circuit
that outputs an adjustment signal (in this embodiment, an
adjustment signal for designating the capacitance of the
variable-capacitance capacitor 53 (FIG. 2)) for designating the
impedance of the matching circuit 11. In the RF tag circuit 10
according to this embodiment, for example, the impedance adjustment
control circuit 14 having the configuration illustrated in FIG. 6
is used.
[0046] While the overall operation of the impedance adjustment
control circuit 14 will be described later, an up counter 61 is a
counter that clears the counter value to "0" when a reset pulse is
input and counts up when an up pulse is input. The counter value of
the up counter 61 is used as an adjustment signal designating the
impedance of the matching circuit 11 (the capacitance of the
variable-capacitance capacitor 53 (FIG. 2)).
[0047] A comparator 62 is a circuit that outputs a result of
comparison between the power supply voltage (the output voltage of
the rectification circuit 12) VOUT and the voltage of a capacitor
63. The output of the comparator 62 is input to the control
unit/storage unit 15 through a CMP_OUT signal line. A switch 64 is
a switch that is controlled such that it is turned on/off by the
control unit/storage unit 15 through a Ctrl signal line.
[0048] FIG. 7 is a diagram illustrating one example of a control
flow of the control unit/storage unit 15 controlling the impedance
adjustment control circuit. The control flow illustrated in FIG. 7
is, for example, started in accordance with an input of an
adjustment trigger from the adjustment trigger generating circuit
16 to the control unit/storage unit 15. Hereinafter, one example of
the control flow of the control unit/storage unit 15 controlling
the impedance adjustment control circuit 14 will be described with
reference to FIG. 7.
[0049] The control unit/storage unit 15 to which an adjustment
trigger has been input, first, outputs a Reset pulse (Step S101).
Accordingly, the count value of the up counter 61 disposed inside
the impedance adjustment control circuit 14 (see FIG. 6) is reset
to "0", and the capacitance of the variable-capacitance capacitor
53 (FIG. 2) disposed inside the matching circuit 11 is adjusted to
a lowest capacitance C.sub.0.
[0050] Next, the control unit/storage unit 15 outputs a Ctrl pulse
(Step S102). That is, the control unit/storage unit 15 causes the
voltage of the capacitor 63 (an input voltage input to a "-"
terminal of the comparator 62) to coincide with the power supply
voltage VOUT at that time point by turning on the switch 64 and
then holds the voltage of the capacitor 63 by turning off the
switch 64.
[0051] Thereafter, the control unit/storage unit 15 outputs an UP
pulse (Step S103) and then determines whether or not the output
CMP_OUT of the comparator 62 is low (Step S104).
[0052] When an UP pulse is input, the count value of the up counter
61 is counted up, and accordingly, the capacitance of the
variable-capacitance capacitor 53 disposed inside the matching
circuit 11 increases. When the impedance of the matching circuit 11
after increasing the capacitance of the variable-capacitance
capacitor 53 does not become an appropriate value, and the
impedance of the matching circuit 11 is close to an appropriate
value, the power supply voltage increases. On the other hand, when
the impedance of the matching circuit 11 after increasing the
capacitance of the variable-capacitance capacitor 53 becomes an
appropriate value, the voltage supply voltage hardly changes. In
addition, when the impedance of the matching circuit 11 after
increasing the capacitance of the variable-capacitance capacitor 53
does not become an appropriate value, and the impedance further
deviates from an appropriate value, the power supply voltage hardly
changes. Accordingly, when the impedance has an appropriate value
or when the impedance further deviates from the appropriate value,
the output CMP_OUT becomes low. For this reason, when the output
CMP_OUT is low, since the impedance has an appropriate value, or in
order to suppress the impedance from further deviating from the
appropriate value, the impedance adjustment of the matching circuit
11 is completed. On the other hand, when the impedance of the
matching circuit 11 does not have an appropriate value, and the
impedance of the matching circuit 11 is close to an appropriate
value, the output CMP_OUT becomes high. For this reason, when the
output CMP_OUT is high, the impedance adjustment of the matching
circuit 11 is not completed, and the impedance adjustment continues
to be executed.
[0053] For this reason, when the output CMP_OUT of the comparator
62 is high (Step S104: No), the control unit/storage unit 15
restarts the process of Step S103 and subsequent steps. Then, when
the output CMP_OUT of the comparator 62 becomes low (Step S104:
Yes), the control unit/storage unit 15 ends this impedance
adjusting process (the process illustrated in FIG. 7).
[0054] FIG. 8 is a diagram illustrating one example of variations
in a power supply voltage input from the rectification circuit 12
to the impedance adjustment control circuit 14 when an impedance of
the matching circuit 11 is close to an appropriate value. In FIG.
8, variations in the power supply voltages input from the
rectification circuit 12 to the impedance adjustment control
circuit 14 in a case in which the time constant of the RF tag
circuit 10 is large and a case in which the time constant is small
are compared with each other. As exemplified in FIG. 8, when the
time constant is small, when the impedance value of the matching
circuit 11 increases, the power supply voltage increases within a
period in which the control unit/storage unit 15 detects an
increase in the power supply voltage, and accordingly, the control
unit/storage unit 15 can detect the increase in the power supply
voltage. For this reason, the control unit/storage unit 15 can
determine that impedances are in a mismatch state between the
antenna 20 and the RF tag circuit 10. A change in the power supply
voltage becomes gentler as the time constant further increases.
Thus, when the time constant becomes large to some degree, it is
difficult to detect an increase in the power supply voltage
accompanying an increase in the impedance value within the period
in which the control unit/storage unit 15 detects an increase in
the power supply voltage. For this reason, even when there actually
is impedance mismatch between the antenna 20 and the circuit
disposed inside the RF tag circuit 10, the control unit/storage
unit 15 does not detect an increase in the power supply voltage,
and accordingly, it may be erroneously detected that there is
impedance matching therebetween. Thus, in the RF tag circuit 10
according to the embodiment, when the impedance is adjusted, a
process of causing the time constant of the RF tag circuit 10 to
approach "0" by disconnecting the capacitor 133 from the circuit by
turning off the SW_C 132 is executed.
[0055] FIG. 9 is a diagram illustrating one example of a processing
flow according to the embodiment. In FIG. 9, the time flows from
the upper side to the lower side of the drawing. Hereinafter, one
example of the processing flow according to the embodiment will be
described with reference to FIG. 9.
[0056] In OP1, the adjustment trigger generating circuit 16
transmits an adjustment trigger to the control unit/storage unit
15. The adjustment trigger is, for example, transmitted by being
triggered by a decrease in the power supply voltage input from the
rectification circuit 12 to the impedance adjustment control
circuit 14 or the like. The control unit/storage unit 15 that has
received an adjustment trigger starts processes of OP2 and
subsequent steps. In OP2, the control unit/storage unit 15
transmits a charge capacitance off signal to the load control
circuit 13. The load control circuit 13 that has received the
charge capacitance off signal turns off the SW_C 132. According to
the process of OP2, the capacitor 133 is disconnected from the RF
tag circuit 10. In OP3, the control unit/storage unit 15 transmits
a load control signal to the load control circuit 13, thereby
turning on the SW_LOAD 131 and causing the normal load 30 to be in
an operating state. Thereafter, the SW_LOAD 131 maintains to be in
the on state until it is turned off in OP7 regardless of the
predetermined cycle at which the normal load 30 is operated.
Hereinafter, in description presented here, causing the SW_LOAD 131
to be on regardless of the predetermined cycle will be referred to
as enforced-on of the SW_LOAD 131. The processes of OP2 and OP3 may
be interchanged in the sequence.
[0057] In OP4, the control unit/storage unit 15 transmits an
adjustment control signal as a start command instructing start of
impedance adjustment. In OP5, the impedance adjustment control
circuit 14 transmits an adjustment signal to the matching circuit
11 and performs impedance adjustment. Details of the impedance
adjustment will be described later. In OP6, the control
unit/storage unit 15 determines that the impedance adjustment has
been completed based on information representing variations in the
power supply voltage that is acquired from the impedance adjustment
control circuit 14. In OP7, the control unit/storage unit 15
releases the enforced-on of the SW_LOAD 131. In other words, as a
result of the process of OP7, the normal load 30 starts to operate
using the predetermined cycle. In OP8, the control unit/storage
unit 15 transmits an instruction for turning on the SW_C 132 to the
load control circuit 13. In accordance with the process of OP8, the
capacitor 133 is connected to the RF tag circuit 10.
[0058] FIG. 10 is a diagram illustrating one example of the
processing flow of impedance adjustment according to the
embodiment. The process exemplified in FIG. 10 is, for example, a
process executed in OP5 illustrated in FIG. 9. In the process
exemplified in FIG. 10, it is assumed that a Reset pulse has
already been transmitted to the up counter 61. Hereinafter, one
example of the processing flow of the impedance adjustment
according to the embodiment will be described with reference to
FIG. 10.
[0059] In OP11, the control unit/storage unit 15 samples and holds
(S/H) the power supply voltage (denoted as a monitoring voltage in
the drawing) input from the rectification circuit 12 to the
impedance adjustment control circuit 14. The process of OP11, for
example, corresponds to the process of S102 illustrated in FIG. 7.
In OP12, the impedance adjustment control circuit 14 transmits an
adjustment signal for increasing the impedance of the matching
circuit 11. The matching circuit 11 that has received the
adjustment signal, for example, increases the impedance of the
matching circuit 11 by .DELTA.Z by changing the capacitance of the
variable-capacitance capacitor 53. The process of OP12, for
example, corresponds to the process of S103 illustrated in FIG. 7.
In OP13, the control unit/storage unit 15 acquires the power supply
voltage after the increase in the impedance in OP12. The control
unit/storage unit 15 determines whether or not a difference between
the power supply voltage acquired in OP12 and the power supply
voltage that is S/H in OP11 is less than .delta.V. Here, .delta.V
is a value that is set in accordance with the resolution of the
comparator 141 of the impedance adjustment control circuit 14. In
addition, W may be a predetermined threshold. When the difference
is less than .delta.V (Yes in OP13), the impedance adjusting
process ends. On the other hand, when the difference is not less
than .delta.V (No in OP13), the process is returned to OP11. The
process of OP13 corresponds to S104 illustrated in FIG. 7. As
exemplified in FIG. 10, the process of OP11 and OP12 is repeated
until an increase width of the power supply voltage becomes less
than the resolution of the comparator 141 or less than a
predetermined threshold, and the impedance of the matching circuit
11 is adjusted.
[0060] FIG. 11 is a diagram illustrating one example of variations
in a power supply voltage input from the rectification circuit 12
to the impedance adjustment control circuit 14 in the embodiment.
In FIG. 11, the vertical axis represents the voltage, and the
horizontal axis represents the time as an example. In addition, in
FIG. 11, a normal load driving period in which the normal load 30
is activated at a predetermined cycle and an adjustment period in
which an impedance is adjusted are illustrated as an example. When
water or the like adheres to the RF tag circuit 10, as exemplified
in FIG. 11, the power supply voltage decreases. The power supply
voltage gently drops in accordance with the influence of a time
constant corresponding to a duty ratio in the operations of the
capacitor 133 and the normal load 30. The duty ratio is, for
example, information representing a ratio of the driving period of
the normal load 30 to a predetermined period. By being triggered by
the reception of an adjustment trigger, the RF tag circuit 10
transitions from the normal load driving period to the adjustment
period. In the adjustment period, the load control circuit 13 that
has received a charge capacitance off signal transmitted from the
control unit/storage unit 15 turns off the SW_C 132, thereby
disconnecting the capacitor 133 from the RF tag circuit 10. When
the capacitor 133 is disconnected from the RF tag circuit 10, the
time constant of the RF tag circuit 10 becomes nearly "0". As a
result, as in the case in which the time constant is small
exemplified in FIG. 8, a change in the power supply voltage after
impedance adjustment occurs within a predetermined period in which
the control unit/storage unit 15 detects a voltage change. For this
reason, the control unit/storage unit 15 can detect an increase in
the power supply voltage after the impedance adjustment. The reason
the power supply voltage increases in a stepped manner in the
adjustment period is that the impedance adjustment control circuit
14 increases the impedance of the matching circuit 11 by AZ each
time. When it is determined that there is impedance matching
between the antenna 20 and the RF tag circuit 10, the RF tag
circuit 10 transitions from the adjustment period to the normal
load driving period.
[0061] According to the embodiment, when the impedance adjustment
is performed, the capacitor 133 is disconnected from the RF tag
circuit 10. For this reason, the influence of the time constant of
the capacitor 133 on variations in the voltage when the impedance
is adjusted is reduced. The time constant is, for example,
calculated using the following Equation 1.
time constant .tau.=C.times.load resistance/load ON/OFF Duty
(Equation 1)
[0062] In Equation 1 represented above, C is capacitance of the
capacitor 133, and a load on/off duty is a duty ratio of the normal
load 30. In addition, in Equation 1, "/ (slash)" included in the
"load ON/OFF duty" does not represent dividing but represents one
value as the "load ON/OFF duty". For example, when the capacitance
of the capacitor 133 is 100 .mu.F, the load resistance of the
normal load 30 is 1 k.OMEGA., and the duty ratio of the normal load
30 is 10%, the time constant T becomes one second in accordance
with Equation 1. For this reason, for example, when the impedance
is adjusted by repeating 16 cycle times of the impedance adjusting
process exemplified in OP11 to OP13 in FIG. 10, 16 seconds is
required for the adjustment of the impedance. Here, as described in
the embodiment, when the capacitor 133 is disconnected from the RF
tag circuit 10, the electrostatic capacitance of the capacitor 133
may be regarded as "0". For this reason, when the capacitor 133 is
disconnected, the time constant .tau. may be regarded as "0", and
thus, a time required for the impedance adjustment is shortened. In
addition, by decreasing the influence of the time constant, a
change in the power supply voltage after the impedance adjustment
occurs within the predetermined period in which the control
unit/storage unit 15 detects a voltage change. As a result,
although the impedance mismatch is not actually solved, the
possibility of erroneous detection of the control unit/storage unit
15 for the completion of the adjustment of the impedance can be
decreased. For this reason, according to the embodiment, even when
the capacitor 133 having high capacitance is employed for stably
operating the normal load 30, the impedance adjustment can be
executed more appropriately.
[0063] In the embodiment, although the normal load 30 is activated
at a predetermined cycle, the normal load may be constantly
operated.
First Modified Example
[0064] According to the embodiment, during the adjustment period in
which impedance adjustment is performed, the capacitor 133 is
disconnected from the RF tag circuit 10, and the normal load 30 is
operated. However, when the normal load 30 is activated at a
predetermined cycle, a resistance value of the normal load 30 at
the predetermined cycle and a resistance value of the normal load
30 continues to be operated during the adjustment period are
different when the duty ratio is considered. For this reason, as
exemplified in FIG. 12, the power supply voltage supplied to the
normal load 30 may drop to an operation lower limit of the normal
load 30 in accordance with a voltage drop at the time of adjusting
the impedance. In such a case, the normal load 30 does not operate,
and accordingly, it is difficult to adjust the impedance. Thus, in
a first modified example, during an adjustment period in which
impedance adjustment is performed, an equivalent load is connected
to the RF tag circuit instead of the normal load 30. A resistance
value of the equivalent load is determined based on the resistance
value of the normal load 30 and the duty ratio of the normal load
30. By using the equivalent load, as exemplified in FIG. 12, a drop
of the power supply voltage can be configured to be smaller than
that of the embodiment. Hereinafter, the first modified example
will be described with reference to the drawings. The same
reference numeral will be assigned to the same component as that of
the embodiment, and description thereof will be omitted.
[0065] FIG. 13 is a diagram illustrating one example of the
configuration of an RF tag circuit 10a according to the first
modified example. In FIG. 13, the reader/writer device 40 is not
illustrated. The RF tag circuit 10a according to the first modified
example is different from the RF tag circuit 10 according to the
embodiment in that, the control unit/storage unit 15 and the load
control circuit 13 are respectively replaced with a control
unit/storage unit 15a and a load control circuit 13a, and an
equivalent load 31 is further connected.
[0066] The control unit/storage unit 15a is different from the
control unit/storage unit 15 according to the embodiment in that,
the control unit/storage unit 15a transmits a load switching
command instructing switching from the normal load 30 to the
equivalent load 31 to the load control circuit 13a. The load
control circuit 13a is different from the load control circuit 13
according to the embodiment in that, the load control circuit 13a
switches from the normal load 30 to the equivalent load 31 in
accordance with a load switching command transmitted from the
control unit/storage unit 15a.
[0067] FIG. 14 is a diagram illustrating one example of the
configuration of the load control circuit 13a according to the
first modified example. The load control circuit 13a is different
from the load control circuit 13 according to the embodiment in
that, the load control circuit 13a is connected to the equivalent
load 31 through an SW2_LOAD 134. When the SW2_LOAD 134 becomes on,
the equivalent load 31 is connected to the load control circuit
13a. When the SW2_LOAD 134 becomes off, the equivalent load 31 is
disconnected from the load control circuit 13a. The switching
between on and off of the SW_LOAD 131, SW_C 132, and SW2_LOAD 134
is executed in accordance with a signal received from the control
unit/storage unit 15a. The SW_LOAD 131 is switched between on and
off at a predetermined cycle in a period other than an impedance
adjustment period and is set off in the impedance adjustment
period. The SW_C 132 is on in a period other than the impedance
adjustment period and is off in the impedance adjustment period.
The SW2_LOAD 134 is off in a period other than the impedance
adjustment period and is on in the impedance adjustment period. In
other words, in the impedance adjustment period, the capacitor 131
is disconnected from the RF tag circuit 10a, and load connection is
switched from the normal load 30 to the equivalent load 31. Here,
the arrangement of various switches including the SW_LOAD 131, the
SW_C 132, and the SW2_LOAD 134 of the load control circuit 13a is
not limited to that of the example illustrated in FIG. 14. For
example, the SW_C 132 and the SW_LOAD 131 may be arranged in
series.
[0068] The equivalent load 31 is a resistance device that has a
resistance component of the normal load 30 and a load resistance
value corresponding to the predeteimined cycle at which the normal
load 30 is activated. The equivalent load 31 may be a
variable-resistance device that may be set as having the resistance
component of the normal load 30 and a load resistance value
corresponding to the predetermined cycle at which the normal load
30 is activated. The resistance value of the equivalent load 31,
for example, can be determined using the following Equation 2.
Equivalent load=normal load/ON/OFF Duty (Equation 2)
[0069] For example, when the resistance value of the normal load 30
is 1 k.OMEGA., and the duty ratio ("ON/OFF duty" in Equation 2) of
the normal load 30 is 10%, the resistance value of the equivalent
load 31 is determined as 10 k.OMEGA. based on Equation (2). The
equivalent load 31 is one example of "substitute load". In
addition, in Equation 2, "/ (slash)" included in "ON/OFF duty" does
not represent dividing but represents one value as the "ON/OFF
duty".
[0070] FIG. 15 is a diagram illustrating one example of a
processing flow according to the first modified example. In FIG.
15, the same reference sign is assigned to the same component as
that illustrated in FIG. 9, and description thereof will be
omitted. Hereinafter, one example of the processing flow according
to the first modified example will be described with reference to
FIG. 15.
[0071] In OP21, the control unit/storage unit 15 instructs the load
control circuit 13a to turn off the SW_LOAD 131 and the SW_C 132.
The load control circuit 13a turns off the SW_LOAD 131 and the SW_C
132 in accordance with the instruction from the control
unit/storage unit 15. Thereafter, in OP24, the normal load 30 is
not activated regardless of the predetermined cycle until the
SW_LOAD 131 is turned on. In accordance with the process of OP21,
the normal load 30 and the capacitor 133 are disconnected from the
RF tag circuit 10a. In OP22, the control unit/storage unit 15
instructs the load control circuit 13a to turn on the SW2_LOAD 134.
The load control circuit 13a turns on the SW2_LOAD 134 in
accordance with the instruction from the control unit/storage unit
15. As a result of the process of OP22, the equivalent load 31 is
connected to the RF tag circuit 10a. The processes of OP21 and OP22
may be interchanged in the sequence.
[0072] In OP23, the control unit/storage unit 15 instructs the load
control circuit 13a to turn off the SW2_LOAD 134. The load control
circuit 13a turns off the SW2_LOAD 134 in accordance with the
instruction from the control unit/storage unit 15. As a result of
the process of OP23, the equivalent load 31 is disconnected from
the RF tag circuit 10a. In OP24, the control unit/storage unit 15
instructs the load control circuit 13a to turn on the SW_LOAD 131
and the SW_C 132. The load control circuit 13a turns on the SW_LOAD
131 and the SW_C 132 in accordance with the instruction from the
control unit/storage unit 15. In accordance with the process of
OP24, the normal load 30 and the capacitor 133 are connected to the
RF tag circuit 10a. After OP24, the normal load 30 is activated at
a predetermined cycle. The processes of OP23 and OP24 may be
interchanged in the sequence.
[0073] FIG. 16 is a diagram illustrating one example of variations
in a power supply voltage input from the rectification circuit 12
to the impedance adjustment control circuit 14 in the first
modified example. In FIG. 16, similar to FIG. 11, the vertical axis
represents the voltage, and the horizontal axis represents the time
as an example. In addition, in FIG. 16, similar to FIG. 11, a
normal load driving period in which the normal load 30 is activated
at a predetermined cycle and an adjustment period in which an
impedance is adjusted are exemplified. In the case illustrated in
FIG. 16, by being triggered by an input of an adjustment trigger,
the normal load 30 is disconnected from the RF tag circuit 10a, and
the equivalent load 31 is connected to the RF tag circuit 10a,
which is different from FIG. 11. According to the first modified
example, the equivalent load 31 is connected instead of the normal
load 30 in the impedance adjustment period, and accordingly, a drop
in the power supply voltage is smaller than that according to the
embodiment.
Second Modified Example
[0074] According to the first modified example, the equivalent load
31 of which the resistance value is determined in advance is used.
According to a second modified example, an equivalent load of which
a resistance value is changeable is employed, and the resistance
value of the equivalent load is dynamically determined based on a
power supply voltage input from the rectification circuit 12 and a
duty ratio of the normal load 30. Hereinafter, the second modified
example will be described with reference to the drawings. The same
reference sign is assigned to the same component as that of the
embodiment or the first modified example, and description thereof
will be omitted.
[0075] FIG. 17 is a diagram illustrating one example of the
configuration of an RF tag circuit 10b according to the second
modified example. In FIG. 17, the reader/writer device 40 is not
illustrated. The RF tag circuit 10b according to the second
modified example is different from the first modified example in
that, the control unit/storage unit 15a is replaced with a control
unit/storage unit 15b, an equivalent load calculating unit 17 is
further included, and an equivalent load 31a replacing the
equivalent load 31 is connected. The equivalent load 31a has a
variable resistance value, and is, for example, an electrical
circuit including a constant current circuit configured by a
variable resistor, a transistor, or the like.
[0076] The control unit/storage unit 15b stores a duty setting and
normal load information of the normal load 30 in a storage unit.
The duty setting includes information representing a duty ratio of
the normal load 30. The normal load information includes at least
one of information representing power consumption of the normal
load 30 and information representing current consumption of the
normal load 30. The control unit/storage unit 15b is different from
the control unit/storage unit 15a according to the first modified
example in that, the control unit/storage unit 15b transmits the
duty setting and the normal load information to the equivalent load
calculating unit 17, which. The equivalent load calculating unit 17
calculates a resistance value to be set in the equivalent load 31a
based on the duty setting and the normal load information input
from the control unit/storage unit 15b and the power supply voltage
input from the rectification circuit 12. The resistance value of
the equivalent load 31a, for example, can be calculated using the
following Equation 3.
Equivalent load [ .OMEGA. ] = DC voltage [ V ] current consumption
of normal load [ A ] .times. Duty setting [ % ] = ( DC voltage [ V
] ) 2 power consumption of normal load [ W ] .times. Duty setting [
% ] ( Equation 3 ) ##EQU00001##
[0077] For example, when it is determined in advance that the DC
voltage (power supply voltage) is 2 V, and the current consumption
of the normal load 30 is 1 A, the control unit/storage unit 15b
stores information representing the power supply voltage and the
current consumption of the normal load and provides the stored
information for the equivalent load calculating unit 17. The
equivalent load calculating unit 17 calculates a resistance value
of the equivalent load 31a using Equation 3 based on the
information provided from the control unit/storage unit 15b and the
power supply voltage input from the rectification circuit 12. The
equivalent load calculating unit 17 may set a resistance value of
the equivalent load 31a such that the calculated resistance value
is obtained.
[0078] In addition, when the duty ratio can be changed to four
levels of 10%, 25%, 50%, and 100%, the resistance value of the
equivalent load 31a may be set to four levels of 20 k.OMEGA., 8
k.OMEGA., 4 k.OMEGA., and 2 k.OMEGA. corresponding to the duty
ratios in accordance with Equation 3. In such a case, the control
unit/storage unit 15b may notify the equivalent load calculating
unit 17 of the current duty setting, and the equivalent load
calculating unit 17 may set a resistance value corresponding to the
notified duty setting in the equivalent load 31a. Alternatively, as
the equivalent load 31a, four kinds of loads including a load of 20
k.OMEGA., a load of 8 k.OMEGA., a load of 4 k.OMEGA., and a load of
2 k.OMEGA. are prepared, and the resistance value of the equivalent
load 31a may be set by connecting a load corresponding to the duty
ratio to the RF tag circuit 10b.
[0079] According to the second modified example, the equivalent
load calculating unit 17 calculates a resistance value to be set in
the equivalent load 31a based on the normal load information and
the duty setting input from the control unit/storage unit 15b and
the power supply voltage input from the rectification circuit 12.
The calculated resistance value is set as the resistance value of
the equivalent load 31a. For this reason, according to the second
modified example, a resistance value of the equivalent load 31a can
be appropriately set even when there are variations in the normal
load information, the duty setting, and the power supply
voltage.
Third Modified Example
[0080] According to the second modified example, the normal load
information is stored in the control unit/storage unit 15b.
According to a third modified example, a current flowing through
the normal load 30 is measured, and an equivalent load calculating
unit calculates a resistance value of the equivalent load by
referring to a result of the measurement of the current.
Hereinafter, the third modified example will be described with
reference to the drawings. The same reference sign is assigned to
the same component as that of the embodiment, the first modified
example, or the second modified example, and description thereof
will be omitted.
[0081] FIG. 18 is a diagram illustrating one example of the
configuration of an RF tag circuit 10c according to the third
modified example. In FIG. 18, the reader/writer device 40 is not
illustrated. The RF tag circuit 10c according to the third modified
example is different from the RF tag circuit 10b according to the
second modified example in that, the control unit/storage unit 15b
and the equivalent load calculating unit 17 are respectively
replaced with a control unit/storage unit 15c and an equivalent
load calculating unit 17a.
[0082] The control unit/storage unit 15c is different from the
control unit/storage unit 15b according to the second modified
example in that the control unit/storage unit 15c transmits the
duty setting to the equivalent load calculating unit 17a but does
not transmit the normal load information. The equivalent load
calculating unit 17a is different from the equivalent load
calculating unit 17 according to the second modified example in
that, the equivalent load calculating unit 17a calculates a
resistance value of the equivalent load 31a based on the duty
setting input from the control unit/storage unit 15c and the result
of the measurement of the current input from the current measuring
circuit 18.
[0083] The current measuring circuit 18 is a circuit that measures
a current flowing through the normal load 30. A specific circuit
configuration of the current measuring circuit 18 is not
particularly limited. FIG. 19 is a diagram illustrating one example
of the configuration of the current measuring circuit 18. The
current measuring circuit 18, for example, as exemplified in FIG.
19, may be a circuit acquired by combining an analog-to-digital
converter (ADC) 177, a comparator 176, and a plurality of resistors
171, 172, 173, 174, and 175. The current measuring circuit 18 is
one example of "measurement unit".
[0084] The equivalent load calculating unit 17, for example, can
calculate a resistance value of the equivalent load 31a using the
following Equation 4.
Equivalent load [ .OMEGA. ] = DC voltage [ V ] l oad current [ A ]
.times. Duty setting [ % ] ( Equation 4 ) ##EQU00002##
[0085] According to the third modified example, a current flowing
through the normal load 30 is measured by the current measuring
circuit 18. For this reason, according to the third modified
example, even when the current flowing through the normal load 30
changes, the resistance value of the equivalent load 31a can be
appropriately set.
Fourth Modified Example
[0086] From the embodiments to the third modified example, the
normal load 30 is activated at a predetermined cycle. In other
words, from the embodiments to the third modified examples, the
duty ratio of the normal load 30 is assumed to be known. In a
fourth modified example, a case will be considered in which the
duty ratio of the normal load 30 varies. According to the fourth
modified example, for example, the normal load 30 is activated in
accordance with an instruction from the reader/writer device 40.
For this reason, in the fourth modified example, the duty setting
is not stored in the RF tag circuit, and the duty ratio of the
normal load 30 may vary due to a communication error between the
reader/writer device 40 and the RF tag circuit or the like. In the
fourth modified example, a configuration capable of appropriately
setting the resistance value of the equivalent load even when the
duty ratio varies will be described. Hereinafter, the fourth
modified example will be described with reference to the drawings.
The same reference sign is assigned to the same component as that
of the embodiments or one of the first to third modified examples,
and description thereof will be omitted.
[0087] FIG. 20 is a diagram illustrating one example of the
configuration of an RF tag circuit 10d according to the fourth
modified example. In FIG. 20, the reader/writer device 40 is not
illustrated. The RF tag circuit 10d according to the fourth
modified example is different from the third modified example in
that, the control unit/storage unit 15c and the equivalent load
calculating unit 17a are respectively replaced with a control
unit/storage unit 15d and an equivalent load calculating unit
17b.
[0088] The control unit/storage unit 15d measures and aggregates
the period during which the normal load 30 is on and the period
during which the normal load 30 is off and calculates an average of
the duty ratios of the normal load 30 based on a result of the
aggregation. The control unit/storage unit 15d transmits an average
value (average duty) of the calculated duty ratios to the
equivalent load calculating unit 17b. The equivalent load
calculating unit 17b calculates a resistance value of the
equivalent load 31a using the average value of the duty ratios
received from the control unit/storage unit 15d. For the
calculation of the resistance value, for example, the received
average value of the duty ratios may be substituted in Equation 2,
Equation 3, or Equation 4.
[0089] According to the fourth modified example, the control
unit/storage unit 15d measures the period during which the normal
load 30 is on and the period during which the normal load 30 is off
and calculates an average of duty ratios of the normal load 30
based on a result of the measurement. For this reason, even when
information relating to a duty ratio is not included in the RF tag
circuit 10d, a duty ratio of the normal load 30 can be calculated.
In addition, since the control unit/storage unit 15d calculates a
duty ratio of the normal load 30, for example, even when the duty
ratio of the normal load 30 varies due to a communication error or
the like when the normal load 30 is activated in accordance with an
instruction from the reader/writer device 40, a duty ratio on which
the influence of such a variation is reflected can be calculated.
For this reason, according to the fourth modified example, even
when the duty ratio varies, a resistance value of the equivalent
load 31a can be appropriately set.
Fifth Modified Example
[0090] FIG. 21 is a diagram illustrating one example of the
configuration of a load control circuit 13b according to a fifth
modified example. In the first to fourth modified examples, the
capacitor 133 is disconnected from the load control circuit when
the impedance is adjusted. In the fifth modified example, when the
impedance is adjusted, the capacitor 133 is disconnected from the
load control circuit, and the capacitor 133 and the normal load 30
are connected. Hereinafter, the fifth modified example will be
described with reference to the drawings.
[0091] According to the fifth modified example, for example, in the
configuration according to the first modified example exemplified
in FIG. 14, a wiring connecting the normal load 30 and the
capacitor 133 is added separately from a wiring passing through the
SW_LOAD 131. In the added wiring, an SW3_LOAD 135 is disposed. The
SW3_LOAD 135 is turned off except during the impedance adjustment.
According to the fifth modified example, when the equivalent load
31 is connected to the load control circuit 13b by turning off the
SW_LOAD 131 and the SW_C 132 and turning on the SW2_LOAD 134, the
control unit/storage unit 15 connects the capacitor 133 and the
normal load 30 by turning on the SW3_LOAD 135. According to the
fifth modified example, electric power is supplied from the
capacitor 133 to the normal load 30 also during the impedance
adjustment. Therefore, even during the impedance adjustment, the
normal load 30 can be continuously operated.
[0092] In the embodiments and the modified examples described
above, the impedance adjustment is performed using a linear search
of monotonously increasing the capacitance of the
variable-capacitance capacitor 53 disposed inside the matching
circuit 11. However, the algorithm of the impedance adjustment is
not limited to the linear search of monotonously increasing the
capacitance of the variable-capacitance capacitor 53. For example,
the impedance adjustment may be performed using a linear search of
monotonously decreasing the capacitance of the variable-capacitance
capacitor 53. In addition, the impedance adjustment may be
performed using an arbitrary search algorithm such as a binary
search or a tree search.
[0093] The embodiment and the modified examples described above may
be combined together.
[0094] It will be apparent to those skilled in the art that various
modifications and variations can be made to the disclosed
embodiments without departing from the scope or spirit of the
disclosure. In view of the foregoing, it is intended that the
disclosure covers modifications and variations provided that they
fall within the scope of the following claims and their
equivalents.
* * * * *