DESCRIPTION
[Title of Invention]
IMPEDANCE STABILIZATION DEVICE
[Technical Field]
[0001]
This application claims the benefits of priority from Japanese Patent
Application No. 2010-091571 and Japanese Patent Application No. 2010-091572,
each filed on April 12, 2010, the disclosure of which, including the claims,
description, drawings and abstract, is incorporated herein by reference in its entirety.
[0002]
The present invention relates to an impedance stabilization device for use in
power line communication.
[Background Art]
[0003]
In recent years, a system for performing power line communication has
been in practical use. In the power line communication, high-frequency signals are
superimposed on a power line (also referred to as a distribution line). The power line
communication is performed using an existing power line without the need for
installation of dedicated wiring to build an indoor communication network, and
therefore is expected to become increasingly popular. Power distribution systems,
however, are normally not designed for use in communication. Therefore, the power
line communication can cause an impedance mismatch to a line (wiring) at an end of
the power distribution system (socket). Once the impedance mismatch is caused,
reflection of high-frequency signals used in the power line communication occurs at
a point where the mismatch is caused. The reflection of high-frequency signals leads
to frequency selective fading that can result in a problem of channel characteristic
degradation in the power line communication.
[0004]

As a power line for use in interior distribution, a power line having
characteristic impedance on the order of approximately 100 ohms is generally used.
[0005]
When a household electrical appliance having impedance of a few ohms to
high-frequency signals is connected to a socket at the end of the power distribution
system, the impedance of the socket becomes extremely lower than the characteristic
impedance of a power line. On the other hand, when no electronic equipment is
connected to the socket, the end becomes an open end. In such a case, the impedance
of the socket becomes extremely higher than the characteristic impedance of the
power line. Accordingly, a mismatch occurs between the impedance to
high-frequency signals in a case where the socket is the open end and the impedance
to the high-frequency signals in a case where the socket is not the open end, at the
end of the power distribution system (socket). As a result, intense reflection of
high-frequency signals occurs, and thus channel characteristic in the power line
communication is degraded.
[0006]
In order to prevent such channel characteristic degradation, a termination
circuit for reducing the impedance mismatch at the socket or the like is disclosed
(see Patent Literature 1).
[0007]
FIG. 25 illustrates a configuration of the termination circuit disclosed in
Patent Literature 1. The configuration of the termination circuit illustrated in FIG. 25
is as follows: an inductor 2503 is directly connected to a line (power line), and a
circuit including a termination resistor 2501 and a capacitor (condenser) 2502
connected in series is connected in parallel with the line. Here, as the termination
resistor 2501, a resistor having resistance approximately equal to the characteristic
impedance of the line is used. Used as the capacitor 2502 is a capacitor having
sufficiently lower impedance than the characteristic impedance of the line to a

high-frequency signal for use in the power line communication, and having
sufficiently higher impedance than the characteristic impedance of the line to a
power current (e.g. an alternating current of 50 Hz and 60 Hz, and a direct current).
Used as the inductor 2503 is an inductor having sufficiently higher impedance than
the characteristic impedance of the line to the high-frequency signal, and having
sufficiently lower impedance than the characteristic impedance of the line to the
power current.
[0008]
The high-frequency signal from a line (wiring) side is provided to the circuit
including the termination resistor 2501 and the capacitor 2502 connected in series,
and output from a signal input-output terminal 2504. The line (wiring) side and a
socket side, to which electronic equipment is connected, are separated from each
other by the inductor 2503 having high characteristic impedance to the
high-frequency signal. Therefore, even when a high-frequency impedance of the
electronic equipment connected to the socket is low, the effect thereof is negligible.
As described above, the termination circuit disclosed in Patent Literature 1 has
impedance approximately equal to the characteristic impedance of the line to the
high-frequency signal, regardless of whether or not any equipment is connected to
the socket. Therefore, the impedance mismatch at the end is reduced, and reflection
of the high-frequency signals is suppressed.
[Citation List]
[Patent Literature]
[0009]
[Patent Literature 1 ]
Japanese Patent Application Publication No. 2002-217797
[Summary of Invention]
[Technical Problem]
[0010]

The problem is that the termination circuit disclosed in Patent Literature 1
cannot be used with the power line communication equipment connected to the
socket, as the high-frequency signal does not arrive at the socket side in the
termination circuit as describe above. Therefore, it is necessary to provide two
terminals, namely a terminal for receiving power and a terminal for receiving
high-frequency signals (the signal input-output terminal 2504), to the termination
circuit disclosed in Patent Literature 1.
[0011]
That is to say, the same socket cannot be used for both of the household
electrical appliance and the power line communication equipment in the termination
circuit disclosed in Patent Literature 1. Therefore, with the technology disclosed in
Patent Literature 1, it is necessary to use another socket to which the termination
circuit is not provided. This makes the termination circuit less convenient. Another
problem is that the power line communication equipment becomes unable to
establish communication when being connected not to the signal input-output
terminal 2504 but to the socket by mistake.
[0012]
The present invention has been conceived in view of such problems. A
purpose of the present invention is to provide an impedance stabilization device that
can be used when the household electrical appliance is connected to the terminal
(socket) and when the power line communication equipment is connected to the
same terminal, while reducing the impedance mismatch regardless of whether or not
electronic equipment is connected to the socket.
[Solution to Problem]
[0013]
In order to solve the above-presented problems, one aspect of the present
invention is an impedance stabilization device used for power line communication
performed by superimposing a high-frequency signal on a power line composed of

at least two lines, the impedance stabilization device comprising: a first circuit that
includes a first impedance element and a high-frequency blocking element
connected in parallel, and is inserted into at least one of the lines; and a second
circuit that includes a second impedance element and a low-frequency blocking
element connected in series, and via which the lines are connected, wherein the
high-frequency blocking element has higher impedance than impedance of the first
impedance element to the high-frequency signal, and has lower impedance than
impedance of the first impedance element to one of a low-frequency alternating
current and a direct current supplied to the power line, and the low-frequency
blocking element has lower impedance than impedance of the second impedance
element to the high-frequency signal, and has higher impedance than impedance of
the second impedance element to one of the low-frequency alternating current and
the direct current.
[Advantageous Effects of Invention]
[0014]
With the above-mentioned configuration, the impedance stabilization device
unifies the input-output terminal of the socket by providing a path of a power current
and a path of a high-frequency signal, and reduces the impedance mismatch
occurring when no equipment is connected to the socket and when equipment
having low high-frequency impedance is connected to the socket, using the parallel
matching impedance element.
[Brief Description of Drawings]
[0015]
FIG. 1 illustrates a configuration of the impedance stabilization device 1 in
Embodiment 1.
FIG. 2A illustrates an equivalent configuration of the impedance
stabilization device 1 to a high-frequency signal. FIG. 2B illustrates an equivalent
configuration of the impedance stabilization device 1 to a power current.

FIG. 3 shows examples of combinations of impedance of each element
included in the impedance stabilization device 1.
FIG. 4 is a circuit diagram illustrating an example of a specific
configuration of the impedance stabilization device 1.
FIG. 5 illustrates a configuration of an impedance stabilization device 50 in
Embodiment 1.
FIG. 6 shows examples of combinations of impedance of each element
included in the impedance stabilization device 50.
FIG. 7A illustrates a configuration of an impedance stabilization device 70
in a modification of Embodiment 1. FIG. 7B illustrates a configuration of an
impedance stabilization device 71 in another modification of Embodiment 1.
FIG. 8 illustrates a configuration of an impedance stabilization device 80 in
yet another modification of Embodiment 1.
FIG. 9 illustrates a configuration of a power distribution system showing a
usage of the impedance stabilization device.
FIG. 10 illustrates an example of a power distribution system having a
daisy-chain configuration.
FIG. 11 is a circuit diagram illustrating an example of a specific
configuration of an impedance stabilization device 110.
FIG. 12 is a circuit diagram illustrating an example of a specific
configuration of an impedance upper circuit 160.
FIG. 13 is a circuit diagram illustrating an example of a specific
configuration of an impedance stabilization device 1300.
FIG. 14 is a circuit diagram illustrating an example of a specific
configuration of an impedance stabilization device 1400.
FIG. 15 is a circuit diagram illustrating an example of a specific
configuration of an impedance stabilization device 1500.
FIG. 16 is a circuit diagram illustrating an example of a specific

configuration of an impedance stabilization device la.
FIG. 17 is an equivalent circuit diagram of the impedance stabilization
device la to the high-frequency signal.
FIG. 18 is a circuit diagram illustrating an example of a specific
configuration of an impedance stabilization device 50a.
FIG. 19 is a circuit diagram illustrating an example of a specific
configuration of an impedance stabilization device 70a.
FIG. 20 illustrates an example of a configuration of an impedance
stabilization device using a midpoint potential GND wire.
FIG. 21 illustrates an example of a configuration of an impedance
stabilization device having a balance level higher than that of the impedance
stabilization device illustrated in FIG. 20.
FIG. 22 illustrates an example of a configuration of an impedance
stabilization device adapting to a three-phase alternating current.
FIG. 23 illustrates an example of a configuration of an impedance
stabilization device using an active element as a series matching impedance element.
FIG. 24 illustrates an example of a configuration of a system using an
impedance stabilization device as a distributor.
FIG. 25 is a circuit diagram of a conventional termination device.
[Description of Embodiments]
[0016]
One aspect of the present invention is a first impedance stabilization device
that is an impedance stabilization device used for power line communication
performed by superimposing a high-frequency signal on a power line composed of
at least two lines, the impedance stabilization device comprising: a first circuit that
includes a first impedance element and a high-frequency blocking element
connected in parallel, and is inserted into at least one of the lines; and a second
circuit that includes a second impedance element and a low-frequency blocking

element connected in series, and via which the lines are connected, wherein the
high-frequency blocking element has higher impedance than impedance of the first
impedance element to the high-frequency signal, and has lower impedance than
impedance of the first impedance element to one of a low-frequency alternating
current and a direct current supplied to the power line, and the low-frequency
blocking element has lower impedance than impedance of the second impedance
element to the high-frequency signal, and has higher impedance than impedance of
the second impedance element to one of the low-frequency alternating current and
the direct current.
[0017]
The first impedance stabilization device unifies the input-output terminal of
the socket by providing a path of a power current and a path of the high-frequency
signal, and reduces the impedance mismatch occurring when no equipment is
connected to the socket and when equipment having low high-frequency impedance
is connected to the socket, using the parallel matching impedance element.
[0018]
Another aspect of the present invention is a second impedance stabilization
device that is the first impedance stabilization device, wherein the first impedance
element comprises two elements connected in series, and one end of the second
circuit is connected to a point between the two elements.
[0019]
Another aspect of the present invention is a third impedance stabilization
device that is the second impedance stabilization device, wherein the first circuit is
inserted into each of the lines, so that the lines are balanced with respect to a ground.
Note that the ground is also referred to as "earth" in the field of electric circuits.
[0020]
Furthermore, another aspect of the present invention is a fourth impedance
stabilization device that is the third impedance stabilization device, wherein the one

end of the second circuit is connected to a point between the two elements of the
first impedance element included in the first circuit inserted into one of the lines,
and the other end of the second circuit is connected to a point between the two
elements of the first impedance element included in the first circuit inserted into
another one of the lines.
[0021]
With the above-mentioned configurations, the impedance stabilization
device increases the balance level of the two lines constituting the power line to the
ground, and thus suppresses the leakage of radio waves from equipment connected
to the socket.
[0022]
Another aspect of the present invention is a fifth impedance stabilization
device that is the first impedance stabilization device, wherein impedance of the first
impedance element is 0.3 to 1.2 times higher than characteristic impedance of the
lines.
[0023]
Another aspect of the present invention is a sixth impedance stabilization
device that is the first impedance stabilization device, wherein impedance of the
second impedance element is 0.6 to 3 times higher than characteristic impedance of
the lines.
[0024]
By setting the impedance of the series matching impedance element and the
impedance of the parallel matching impedance element as mentioned above, the
impedance stabilization device reduces the impedance mismatch to suppress the
reflection of high-frequency signals as much as possible and decreases the signal
loss.
[0025]
Another aspect of the present invention is a seventh impedance stabilization

device that is the first impedance stabilization device being provided in power
distribution equipment having a source connector and a feed connector, wherein the
second circuit further includes a switch connected in series with either the second
impedance element or the low-frequency blocking element, and the switch closes
while no wiring is connected to the feed connector, and opens while wiring is
connected to the feed connector.
[0026]
With this configuration, the impedance stabilization device is applicable to
the power distribution system having the daisy-chain configuration.
[0027]
Another aspect of the present invention is an eighth impedance stabilization
device that is the first impedance stabilization device being provided in power
distribution equipment having a source connector and a feed connector, wherein the
second circuit further includes a switch connected in series with either the second
impedance element or the low-frequency blocking element, and the switch closes
while no wiring is connected to at least one of the source connector and the feed
connector, and opens while wiring is connected to each of the source connector and
the feed connector.
[0028]
With this configuration, it is possible to provide an impedance stabilization
device that is applicable to the power distribution system having the daisy-chain
configuration, and is easily installed regardless of direction in which the impedance
stabilization device is connected.
[0029]
Another aspect of the present invention is a ninth impedance stabilization
device that is an impedance stabilization device used for power line communication
performed by superimposing a high-frequency signal on a power line composed of
at least two lines, and provided in power distribution equipment having a feed

connector, the impedance stabilization device comprising: a first circuit that includes
an impedance element, a low-frequency blocking element and a switch connected in
series, and via which the lines are connected; and an impedance upper circuit that is
inserted between an equipment connector and the lines, wherein the low-frequency
blocking element has lower impedance than impedance of the impedance element to
the high-frequency signal, and has higher impedance than impedance of the
impedance element to one of a low-frequency alternating current and a direct current
supplied to the power line, the impedance upper circuit has impedance that is equal
to or higher than characteristic impedance of the lines to the high-frequency signal,
and has lower impedance than characteristic impedance of the lines to one of the
low-frequency alternating current and the direct current, and the switch closes while
no wiring is connected to the feed connector, and opens while wiring is connected to
the feed connector.
[0030]
With this configuration using the impedance upper circuit, it is possible to
provide an impedance stabilization device that is applicable to the power distribution
system having the daisy-chain configuration and reduces the impedance mismatch.
[0031]
Another aspect of the present invention is a tenth impedance stabilization
device that is an impedance stabilization device used for power line communication
performed by superimposing a high-frequency signal on a power line composed of
at least two lines, and provided in power distribution equipment having a source
connector and a feed connector, the impedance stabilization device comprising: a
first circuit that includes an impedance element, a low-frequency blocking element
and a switch connected in series, and via which the lines are connected; and an
impedance upper circuit that is inserted between an equipment connector and the
lines, wherein the low-frequency blocking element has lower impedance than
impedance of the impedance element to the high-frequency signal, and has higher

impedance than impedance of the impedance element to one of a low-frequency
alternating current and a direct current supplied to the power line, the impedance
upper circuit has impedance that is equal to or higher than characteristic impedance
of the lines to the high-frequency signal, and has lower impedance than
characteristic impedance of the lines to one of the low-frequency alternating current
and the direct current, and the switch closes while no wiring is connected to at least
one of the source connector and the feed connector, and opens while wiring is
connected to each of the source connector and the feed connector.
[0032]
With this configuration using the impedance upper circuit, it is possible to
provide an impedance stabilization device that reduces the impedance mismatch, is
applicable to the power distribution system having the daisy-chain configuration,
and is connected in any direction.
[0033]
Another aspect of the present invention is an eleventh impedance
stabilization device that is the seventh or the eighth impedance stabilization device,
wherein at least part of the impedance upper circuit doubles as the impedance
element.
[0034]
With this configuration, the number of elements required to be included in
the impedance stabilization device is reduced as it is unnecessary to provide another
element serving as a matching impedance element.
[0035]
Yet another aspect of the present invention is a twelfth impedance
stabilization device that is an impedance stabilization device used for power line
communication performed by superimposing a high-frequency signal on a power
line composed of at least two lines, the impedance stabilization device comprising: a
first impedance element that is inserted into at least one of the lines; a second

impedance element that connects the lines; a high-frequency blocking element that is
inserted into at least one of a first line and a second line other than the at least two
lines, the first line being connected to the at least one line into which the first
impedance element is inserted so as to bridge the first impedance element and to be
in parallel with the at least one line into which the first impedance element is
inserted, the second line being connected to another line to which the first line is not
connected so as to bridge a point where the second impedance element connects to
the other line and to be in parallel with the other line to which the first line is not
connected; and a low-frequency blocking element that connects the first and second
lines, wherein the high-frequency blocking element has higher impedance than
impedance of the first impedance element to the high-frequency signal, and has
lower impedance than impedance of the first impedance element to one of a
low-frequency alternating current and a direct current supplied to the power line, and
the low-frequency blocking element has lower impedance than impedance of the
second impedance element to the high-frequency signal, and has higher impedance
than impedance of the second impedance element to one of the low-frequency
alternating current and the direct current.
[0036]
The twelfth impedance stabilization device unifies the input-output terminal
of the socket by providing a path of a power current and a path of the
high-frequency signal, and reduces the impedance mismatch occurring when no
equipment is connected to the socket and when equipment having low
high-frequency impedance is connected to the socket, using the parallel matching
impedance element.

The following describes an impedance stabilization device in Embodiment 1
of the present invention, with reference to the drawings.
[0037]

FIG. 1 is a block diagram illustrating a configuration of an impedance
stabilization device 1.
[0038]
As illustrated in FIG. 1, the impedance stabilization device 1 is inserted
between a line (power source) side and an equipment (communication equipment or
household electrical appliance) side. In a power distribution system, a power line is
basically composed of two lines, and the impedance stabilization device 1 is
connected to the lines in the vicinity of a socket.
[0039]
The impedance stabilization device 1 includes series matching impedance
elements 11a, lib, 12a and 12b, a parallel matching impedance element 13, a
low-frequency blocking element 14, and high-frequency blocking elements 15a and
15b.
[0040]
As illustrated in FIG. 1, the series matching impedance element 11a is
connected in series with the series matching impedance element 12a, and the
high-frequency blocking element 15a is connected in parallel with the impedance
elements 11a and 12a connected in series. The series matching impedance elements
11a and 12a and the high-frequency blocking element 15a constitute a first circuit,
and the first circuit is inserted into a line 10a. Note that, in the present description,
the term "series" in the series matching impedance element indicates that the series
matching impedance element is inserted in series into the line. Also, the term
"matching" generally indicates that the impedance of the line side matches the
impedance of the equipment side. In the present description, however, the term
"matching" indicates that the impedance of the line side matches the impedance of
the equipment side as much as possible, and therefore they may not match perfectly
as long as the purpose of the present invention is achieved.
[0041]

The series matching impedance element 1 lb is connected in series with the
series matching impedance element 12b, and the high-frequency blocking element
15b is connected in parallel with the impedance elements 1 lb and 12b connected in
series. The series matching impedance elements 1 lb and 12b and the high-frequency
blocking element 15b constitute another first circuit, and the other first circuit is
inserted into a line 10b.
[0042]
A second circuit including the parallel matching impedance element 13 and
the low-frequency blocking element 14 connected in series is inserted so as to
connect the two lines 10a and 10b. Note that, in the present description, the term
"parallel" in the parallel matching impedance element indicates that, when any
equipment is connected to a terminal at the equipment side, the parallel matching
impedance element is parallel with the connected equipment.
[0043]
As each of the series matching impedance elements 11a, lib, 12a and 12b
and the parallel matching impedance element 13, a resistance element is typically
used.
[0044]
As the low-frequency blocking element 14, a capacitor is typically used. As
each of the high-frequency signal blocking elements 15a and 15b, an inductor is
typically used.
[0045]
The high-frequency blocking elements 15a and 15b are configured to have
sufficiently lower impedance than the impedance of the series matching impedance
elements 11a, lib, 12a and 12b to one of a low-frequency alternating current (e.g.
50 Hz and 60 Hz) and a direct current. On the other hand, the low-frequency
blocking element 14 is configured to have sufficiently higher impedance than the
impedance of the series matching impedance elements 11a, 1 lb, 12a and 12b to one

of a low-frequency alternating current (e.g. 50 Hz and 60 Hz) and a direct current.
[0046]
Here, the expression "sufficiently" in the sentence "the high-frequency
blocking elements 15a and 15b are configured to have sufficiently lower impedance
than the impedance of the series matching impedance elements 11a, lib, 12a and
12b to one of a low-frequency alternating current (e.g. 50 Hz and 60 Hz) and a direct
current" indicates that the impedance of the high-frequency blocking elements 15a
and 15b is low to the extent that a power current cannot flow through the series
matching impedance elements 11a, 1 lb, 12a and 12b, and mainly flows through the
high-frequency blocking elements 15a and 15b. In other words, the high-frequency
blocking elements 15a and 15b have negligible impedance compared to the series
matching impedance elements 11a, lib, 12a and 12b to one of a low-frequency
alternating current (e.g. 50 Hz and 60 Hz) and a direct current. Also, the expression
"sufficiently" in the sentence "the low-frequency blocking element 14 is configured
to have sufficiently higher impedance than the impedance of the series matching
impedance elements 11a, lib, 12a and 12b to one of a low-frequency alternating
current (e.g. 50 Hz and 60 Hz) and a direct current" indicates that the impedance of
the low-frequency blocking element 14 is high to the extent that a power current can
rarely flow through the low-frequency blocking element 14. In other words, the
series matching impedance elements 11a, lib, 12a and 12b have negligible
impedance compared to the low-frequency blocking element 14 to one of a
low-frequency alternating current (e.g. 50 Hz and 60 Hz) and a direct current.
[0047]
With such a configuration, the power current is supplied to the equipment
side through the high-frequency blocking element 15 and rarely flows through the
series matching impedance elements 11a, lib, 12a and 12b and the parallel
matching impedance element 13. Therefore, a loss of the power current (e.g. an
alternating current of 50 Hz and 60 Hz and a direct current) rarely occurs in the

impedance stabilization device 1.
[0048]
In contrast, the high-frequency blocking elements 15a and 15b are
configured to have sufficiently higher impedance than the impedance of the series
matching impedance elements 11a, lib, 12a and 12b to a high-frequency signal.
Also, the low-frequency blocking element 14 has sufficiently lower impedance than
the impedance of the parallel matching impedance element 13 to a high-frequency
signal.
[0049]
Here, the expression "sufficiently" in the sentence "the high-frequency
blocking elements 15a and 15b are configured to have sufficiently higher impedance
than the impedance of the series matching impedance elements 11a, lib, 12a and
12b to a high-frequency signal" indicates that the impedance of the high-frequency
blocking element 15a and 15b is high to the extent that a high-frequency signal can
rarely flow through the high-frequency blocking element 15a and 15b, and mainly
flows through the series matching impedance elements 11a, lib, 12a and 12b. In
other words, the series matching impedance elements 11a, lib, 12a and 12b have
negligible impedance compared to the high-frequency blocking elements 15a and
15b to a high-frequency signal. Also, the expression "sufficiently" in the sentence
"the low-frequency blocking element 14 has sufficiently lower impedance than the
impedance of the parallel matching impedance element 13 to a high-frequency
signal" indicates that the impedance of the low-frequency blocking element 14 is
low to the extent that a high-frequency signal flows through the low-frequency
blocking element 14. In other words, the low-frequency blocking element 14 has
negligible impedance compared to the parallel matching impedance element 13 to a
high-frequency signal.
[0050]
Therefore, a configuration of the impedance stabilization device 1 to a

high-frequency signal is represented by an approximate equivalent circuit as
illustrated in FIG. 2A including only the series matching impedance elements 11a,
lib, 12a and 12b, and the parallel matching impedance 13. Similarly, a
configuration of the impedance stabilization device 1 to one of a low-frequency
alternating current (e.g. 50 Hz and 60 Hz) and a direct current is represented by an
approximate equivalent circuit as illustrated in FIG. 2B including only the
high-frequency blocking elements 15a and 15b.
[0051]
That is to say, the impedance stabilization device 1 has a configuration in
which a path of a high-frequency signal (a path running through the series matching
impedance elements 11a, 1 lb, 12a and 12b) is connected in parallel with a path of a
low-frequency signal, namely the power current (a path running through the
high-frequency blocking elements 15a and 15b). With such a configuration, both of
the signals are transmitted to a common output terminal, namely the socket.
[0052]
Note that, although the impedance stabilization device 1 in Embodiment 1
has a configuration in which a series matching impedance element is connected in
series with each of the lines 10a and 10b, the impedance stabilization device 1 may
have a configuration in which the series matching impedance element is connected
with only one of the lines 10a and 10b. However, imbalance between the two lines
10a and 10b to the ground can cause leakage of radio waves as a possibility of
generating a common mode current increases. In order to prevent such a problem, in
the impedance stabilization device 1 in Embodiment 1, the series matching
impedance elements 11a and 12a are each connected to the line 10a and the series
matching impedance elements lib and 12b are each connected to the line 10b so
that the lines 10a and 10b are balanced to the ground, as illustrated in FIG. 1. With
such a configuration, a balance level of the impedance stabilization device 1 is
maintained at a high level and the leakage of radio waves is suppressed.

[0053]
The following describes a desirable value that each impedance element and
the like should take at the end of the power distribution system, i.e. the impedance
stabilization device 1, in order not to cause the mismatch on a line. For the sake of
simplicity, the description is made using a configuration illustrated in FIG. 2A,
which is an equivalent circuit of the impedance stabilization device 1 to a
high-frequency signal.
[0054]
First, in a case where no equipment is connected to a terminal on the
equipment side, i.e., in a case where no equipment is connected to the socket and
thus the socket is an open end, the impedance of the impedance stabilization device
1 on the line side is expressed in Equation (1) shown below.
[0055]
[Equation 1]

In a case where the terminal on the equipment side is an open end, a
high-frequency signal flows through the series matching impedance element 11 a, the
parallel matching impedance element 13 and the series matching impedance element
lib.
[0056]
In Equation (1), RSi represents total impedance of elements connected to the
lines 10a and 10b in this case (the series matching impedance element 11a and the
series matching impedance element lib). The impedance of the series matching
impedance elements 12a and 12b is negligible as the terminal on the equipment side

is an open end and thus a signal does not flow through these elements.
[0057]
Also, in Equation (1) shown above, RP represents total impedance of
elements included in a second circuit connecting the lines 10a and 10b (the parallel
matching impedance element 13). Note that, in the case shown in FIG. 1, RP
represents total impedance of the parallel matching impedance element 13 and the
low-frequency blocking element 14. The impedance of the low-frequency blocking
element 14 to a high-frequency signal, however, is negligible.
[0058]
In a case where the impedance stabilization device 1 is short-circuited to a
high-frequency signal as equipment having an extremely low high-frequency
impedance is connected to the terminal on the equipment side, namely the socket,
the impedance of the impedance stabilization device 1 on the line side is expressed
in Equation (2) shown below.
[0059]
[Equation 2]

In Equation (2) shown above, Rsi represents total impedance of the series
matching impedance elements 11a and 1 lb. Also, RS2 represents total impedance of
the series matching impedance elements 12a and 12b. RP represents impedance of
the parallel matching impedance element.
[0060]
The amplitude of a reflected wave is generally represented by VSWR

(Voltage Standing Wave Ratio). The value of VSWR of "1" indicates that the
reflection does not occur. Therefore, VSWR can be used as an indicator of a degree
of the impedance mismatch.
[0061]
In the case where the terminal on the equipment side is an open end, VSWR
of the impedance stabilization device 1 on the line side is represented as ZOPEN/Z0
(hereinafter, referred to as "VSWROPEN") using ZCPEN, which is calculated using
Equation (1) shown above, and Z0, which is characteristic impedance of the line. On
the other hand, in the case where the impedance stabilization device 1 is
short-circuited as an household electrical appliance having an extremely low
high-frequency impedance is connected to the terminal on the equipment side,
VSWR of the impedance stabilization device 1 on the line side is represented as
ZSHORT/ZO (hereinafter, referred to as "VSWRSHORT") using ZSHORT> which is
calculated using Equation (2) shown above, and Z0, which is the characteristic
impedance of the line.
[0062]
When the higher of values VSWROPEN and VSWRSHORT is referred to as
VSWRMAX in a case where an impedance value of each element is the same,
VSWRMAX is used as the indicator of a degree of the impedance mismatch occurring
in the impedance stabilization device 1 as described above. That is to say, the closer
the value of VSWRMAx is to 1, the more stable the impedance is and the less the
impedance mismatch occurs when a load is connected. Therefore, the reflection is
suppressed.
[0063]
Accordingly, in order to bring the value of VSWRMAX closer to "1", it is
desirable that the impedance value of each matching impedance element (11a, lib,
12a, 12b and 13) be set so that each of the values of VSWRQPEN and VSWRSHORT is
brought closer to "1".

[0064]
Also, as described above, there are requirements that should be met in order
for both of the high-frequency signal and the power current to reach the equipment
side. An example of the impedance value of each matching impedance element set
so as to meet the requirements is shown in FIG. 3, together with the value of
VSWRMAX and signal loss associated with the impedance value.
[0065]
As can be seen from a table shown in FIG. 3, as the value of VSWRMAX
decreases, the signal loss increases. That is to say, the value of VSWR and the signal
loss are traded off.
[0066]
It is generally known that, when the value of VSWR is equal to or lower
than "2", characteristic degradation is sufficiently prevented. It is also known that,
even when the value of VSWR is approximately "3", characteristics are significantly
improved compared with a case where the terminal on the equipment side is an open
end and a case where the impedance stabilization device 1 is short-circuited.
Therefore, in Embodiment 1, the impedance value of each impedance element is set
so that the value of VSWRMAX is equal to or lower than "3".
[0067]
In order not to greatly degrade the communication performance, it is
preferable that the signal loss be approximately equal to or lower than 3 dB. It is
possible, however, to establish communication when a required value of S/N
(Signal-to-Noise ratio) is met within a dynamic range of a receiver. For example, in
a case of in-home power line communication, in which the signal loss is
approximately 30 dB, a communication signal having the S/N value of 80 dBuV/10
kHz at a transmission point has the S/N value of 50 dBuV/10 kHz at a reception
point. An average noise level of a home appliance or the like on a power line is
approximately 20 to 30 dBuV. Therefore, the S/N value at the reception point will

become 20 to 30 dB. When the required S/N value for establishing communication
is 10 dB, the impedance value of each impedance element is set so that the signal
loss occurring in the impedance stabilization device 1 is approximately equal to or
lower than 10 dB.
[0068]
Therefore, the impedance value of each impedance element included in the
impedance stabilization device 1 is set, with reference to the table shown in FIG.3 in
view of the above, as follows:
Total impedance of the series matching impedance elements (total
impedance of the series matching impedance elements 1 la, 1 lb, 12a and 12b) is 0.3
(0.17 + 0.17) to 1.2 (0.54 + 0.54) times higher than the characteristic impedance of
the line; and
[0069]
Impedance of the parallel matching impedance element is 0.6 to 3 times
higher than the characteristic impedance of the line.
[0070]
These are the requirements that each impedance value should meet.
[0071]
The table in FIG. 3 shows the values of VSWRMAX and the signal losses in a
case where the impedance stabilization device 1 is configured so that the value of
RSi is equivalent to the value of RS2. This is to increase stability of the impedance
stabilization device by equalizing a balance level of the line side and that of the
equipment side to the ground as much as possible, as described above. The value of
RS1, however, may not be equivalent to the value of Rs as long as the purpose of the
present invention (i.e. to unify a terminal for outputting a power current and a
terminal for outputting a high-frequency signal, and to reduce the impedance
mismatch occurring in the impedance stabilization device 1) is achieved.
[0072]

That is to say, the value of RS) may be higher than that of RS2 and vice versa.
Alternatively, one of the values of RSi and RS2 may be set to "0".
[0073]
FIG. 5 illustrates an example of a configuration of a circuit of an impedance
stabilization device 50 in which the value of RS2 is set to "0".
[0074]
As illustrated in FIG. 5, the impedance stabilization device 50 includes the
series matching impedance elements 11a and lib, the parallel matching impedance
element 13, the low-frequency blocking element 14 and the high-frequency blocking
elements 15a and 15b. The impedance stabilization device 50 illustrated in FIG. 5
has a configuration in which the series matching impedance elements 12a and 12b
are eliminated from the impedance stabilization device 1.
[0075]
The impedance stabilization device 50 ensures the path of a high-frequency
signal (the path running through the series matching impedance elements 11a and
1 lb) and the path of a power current (the path running through the high-frequency
blocking elements 15a and 15b), and unifies output terminals at the socket. The
impedance stabilization device 50 achieves a configuration to reduce the impedance
mismatch by connecting the parallel matching impedance element 13 to each of the
lines 10a and 10b.
[0076]
The impedance stabilization devices 50 and 1 have similar configurations in
that (i) the high-frequency blocking elements 15a and 15b are configured to have
sufficiently lower impedance than the impedance of the series matching impedance
elements 11a and lib to one of a low-frequency alternating current (e.g. 50 Hz and
60 Hz) and a direct current, and to have sufficiently higher impedance than the
impedance of the series matching impedance elements 11a and lib to a
high-frequency signal, and (ii) the low-frequency blocking element 14 is configured

to have sufficiently higher impedance than the impedance of the parallel matching
impedance element 13 to one of a low-frequency alternating current (e.g. 50 Hz and
60 Hz) and a direct current, and to have sufficiently lower impedance than the
impedance of the series matching impedance elements 11a and lib to a
high-frequency signal. It is then necessary to determine the impedance value so that
the impedance stabilization device 50 shown in FIG. 5 can reduce the impedance
mismatch and decrease the signal loss.
[0077]
FIG. 6 shows the impedance value of each of the series matching impedance
elements 11a and lib and the parallel matching impedance element 13, together
with the value of VSWRMAX and the signal loss associated with the impedance value.
As previously described, it is preferable that the value of VSWRMAX be close to "1",
and the signal loss be small.
[0078]
Considering the fact that the value of VSWRMAX is preferably equal to or
lower than "3" and the signal loss is equal to or lower than 10 dB in the impedance
stabilization device 50, similarly to the impedance stabilization device 1, the
requirements that the impedance value of each matching impedance element
included in the impedance stabilization device 50 should meet are as follows:
[0079]
Total impedance of the series matching impedance elements is 0.3 to 0.9
times higher than the characteristic impedance of the line; and
[0080]
Impedance of the parallel matching impedance element is 0.3 to 3 times
higher than the characteristic impedance of the line.
[0081]
As a result, in view of the requirements that each impedance value should
meet in the impedance stabilization devices 1 and 50, it is desirable that the

impedance values of the series matching impedance element and the parallel
matching impedance element meet the following requirements:
Total impedance of the series matching impedance elements is 0.3 to 1.2
times higher than the characteristic impedance of the line; and
[0082]
Impedance of the parallel matching impedance element is 0.3 to 3 times
higher than the characteristic impedance of the line.
[0083]
These are the two requirements that each impedance value should meet.

As illustrated in FIGs. 1 and 5, the impedance stabilization device in
Embodiment 1 has the following configuration. The first circuit including the series
matching impedance elements (11a and 12a (lib and 12b)) and the high-frequency
blocking element (15a (15b)) connected in parallel is inserted into the line (10a
(10b)) constituting the power line. The two lines (10a and 10b) constituting the
power line are connected via the second circuit including the parallel matching
impedance element (13) and the low-frequency blocking element (14) connected in
series. It is also possible to say that the second circuit, which includes the parallel
matching impedance element (13) and the low-frequency blocking element (14)
connected in series, is connected so as to be in parallel with equipment connected to
the socket on the line in the power distribution system.
[0084]
In this case, the high-frequency blocking element (15a (15b)) is configured
to have sufficiently lower impedance than the impedance of the series matching
impedance elements (11a, lib, 12a and 12b) to one of a low-frequency alternating
current (e.g. 50 Hz and 60 Hz) and a direct current, and to have sufficiently higher
impedance than the impedance of the series matching impedance elements (11a, 1 lb,
12a and 12b) to a high-frequency signal. Also, the low-frequency blocking element

(14) is configured to have sufficiently higher impedance than the impedance of the
series matching impedance elements (11a, lib, 12a and 12b) to one of a
low-frequency alternating current (e.g. 50 Hz and 60 Hz) and a direct current, and to
have sufficiently lower impedance than the impedance of the parallel matching
impedance element (13) to a high-frequency signal.
[0085]
With such a configuration, the path of a high-frequency signal and the path
of a power current are provided, and the power current and the high-frequency
signal are surely transmitted to the equipment side connecting to the socket.
[0086]
Also, the total impedance of the series matching impedance elements (11a,
1 lb, 12a and 12b) is 0.3 to 1.2 times higher than the characteristic impedance of the
line, and the impedance of the parallel matching impedance element (13) is 0.3 to 3
times higher than the characteristic impedance of the line. With such a configuration,
the impedance mismatch is reduced as much as possible at a point where the
impedance stabilization device is provided to the power distribution system.
Therefore, since the reflection of high-frequency signals is suppressed, degradation
of the communication performance is suppressed.

The following describes other configurations than those described in
Embodiment 1 (see FIGs. 1 and 5) that the impedance stabilization device can have.
Note that, for each impedance stabilization device, differences from the impedance
stabilization device 1 are mainly described here.
[0087]
FIGs. 7A, 7B and 8 each illustrate examples of a configuration that the
impedance stabilization device can have.
[0088]
First, description is made on an impedance stabilization device 70 illustrated

in FIG. 7A.
[0089]
The impedance stabilization device 70 includes the series matching
impedance elements 11a, lib, 12a and 12b, the parallel matching impedance
element 13, the low-frequency blocking element 14, and the high-frequency
blocking elements 15a, 15b, 15c and 15d, as illustrated in FIG. 7A.
[0090]
The impedance stabilization device 70 differs from the impedance
stabilization device 1 in that each series matching impedance element is connected
in parallel with a corresponding one of the high-frequency blocking elements 15 a,
15b, 15c and 15d.
[0091]
In a case of the impedance stabilization device 70 illustrated in FIG. 7A, the
number of elements simply increases compared with the impedance stabilization
device 1. However, by using a device in which the high-frequency blocking element
is integrated with the series matching impedance element, the number of elements is
reduced compared with the impedance stabilization device 1 illustrated in FIG. 1.
[0092]
Note that, as an impedance stabilization device 71 illustrated in FIG. 7B, the
impedance stabilization device 70 may have a configuration in which each matching
impedance element is connected in parallel with a corresponding one of the
low-frequency blocking elements and the high-frequency blocking elements. The
impedance stabilization device 71 having such a configuration provides a similar
effect to that provided by the impedance stabilization device 70. Furthermore, a
low-frequency current flowing through each series matching impedance element is
further suppressed by inserting a low-frequency blocking element such as a
condenser in series into one or more of the series matching impedance elements 11a
and 1 lb on the line side and the series matching impedance elements 12a and 12b on

the equipment side, although illustration of such a configuration is omitted.
Similarly to the circuit illustrated in FIG. 7B, the circuit illustrated in FIG. 5 may
have a configuration in which a circuit including the series matching impedance
elements and the parallel matching impedance elements is connected in parallel with
a circuit including the low-frequency blocking elements and the high-frequency
blocking elements. The circuit having such a configuration also provides a similar
effect to that provided by the circuit illustrated in FIG. 5.
[0093]
The impedance stabilization device may be configured as illustrated in FIG.
8. An impedance stabilization device 80 illustrated in FIG. 8 includes the series
matching impedance elements 11a and 12a, the parallel matching impedance
element 13, the low-frequency blocking element 14 and the high-frequency blocking
element 15.
[0094]
The impedance stabilization device 80 differs from the impedance
stabilization device 1 illustrated in FIG. 1 in that the circuit including the series
matching impedance elements lib and 12b, and the high-frequency blocking
element 15b connected in parallel is not inserted in series with the line 10b
constituting the power line.
[0095]
Even when the impedance stabilization device has such a configuration, the
impedance stabilization device is configured so that the power current and the
high-frequency signal are output from the same terminal, and the reflection of
high-frequency signals are suppressed as long as the requirements described in
Embodiment 1 are met.
[0096]
With such a configuration, the number of elements included in the
impedance stabilization device 80 is reduced compared with the impedance

stabilization device 1. However, since the impedance stabilization device 80 has a
configuration in which the series matching impedance elements are connected to
only one of the lines 10a and 10b, a problem of reduction in balance level can occur.
[0097]
In order to solve the above-mentioned problem, a CMC (Common Mode
Choke) 18 may be provided on the power distribution system (or inside the
impedance stabilization device 80) as illustrated in FIG. 8. The CMC 18 has a
function of blocking in-phase currents flowing through the power line on the line
side, and thus largely suppresses the leakage of radio waves. Note that the number of
elements is further reduced by setting the value of RS) or RS2 to "0" in this
configuration.

Here, a usage of the impedance stabilization devices in Embodiment 1 and
modifications of Embodiment 1 is shown in FIG. 9. FIG. 9 illustrates an example of
a configuration of a power distribution system using the impedance stabilization
device.
[0098]
As illustrated in FIG. 9, the power distribution system has a configuration in
which the power current is supplied from a distribution switchboard 5 to a socket
connector 2a of a socket device 3a and a socket connector 2b of a socket device 3b
through a line 4. An impedance stabilization device la is at a position closer to the
line than the socket connector 2a is. An impedance stabilization device lb is at a
position closer to the line than the socket connector 2b is. Each of the impedance
stabilization devices la and lb illustrated in FIG. 9 has a configuration illustrated in
one of FIGs. 1, 5, 7A, 7B and 8.
[0099]
As illustrated in FIG. 9, the impedance stabilization devices are in
one-to-one correspondence with sockets in the power distribution system. With such

a configuration, although a terminal for outputting the power current and a terminal
for outputting the high-frequency signal is the same in each socket, each socket
receives both of the power current and the high-frequency signal, and the power
distribution system reduces the impedance mismatch occurring at the socket.
[0100]
Note that the number of socket devices each including socket connectors
and the number of impedance stabilization devices being in one-to-one
correspondence with the socket devices are not limited to those illustrated in FIG. 9.
The impedance stabilization device is sometimes referred to as a "termination
device" as it is positioned at a terminal of the power distribution system as
illustrated in FIG. 9.
[0101]

In Embodiment 1 described above, the impedance stabilization device is
configured assuming that the impedance stabilization device is at the terminal of the
power distribution system. The impedance stabilization device in Embodiment 1,
however, can cause a problem in a case where a socket to which the impedance
stabilization device is to be connected is in the midst of the power line, namely, in a
case where the impedance stabilization device is not at the terminal.
[0102]
Specifically, the impedance stabilization device in Embodiment 1 is
unsuitable for a case where socket devices are connected with one another via a line
in a daisy chain as illustrated in FIG. 10.
[0103]
The reason therefor is as follows. Suppose that the impedance stabilization
device in Embodiment 1 is connected to each socket (3c, 3d and 3e) in the power
distribution system having a configuration illustrated in FIG. 10. In this case, if any
equipment is connected to the socket 3e for example, the equipment is in parallel

with wiring. Therefore, the impedance mismatch occurs at the socket 3c or the
socket 3d. As described above, the impedance mismatch can cause the reflection of
high-frequency signals and degrade the communication performance.
[0104]
As a solution to the above problem, Embodiment 2 discloses an impedance
stabilization device that uses only the socket as a terminal for outputting the power
current and the high-frequency signal described in Embodiment 1, and that reduces
the impedance mismatch even when being used in the system having a daisy-chain
configuration as illustrated in FIG. 10.
[0105]
FIG. 11 illustrates an example of a configuration of a wiring device
including the impedance stabilization device in the power distribution system in
Embodiment 2. The wiring device corresponds to each of the sockets 3c, 3d and 3e
in the power distribution system illustrated in FIG. 10.
[0106]
As illustrated in FIG. 11, a socket device 3 as the wiring device includes
source connectors 100a and 100b, feed connectors 100c and lOOd, and a socket
connector (also referred to as an "equipment connector") 2. The source connectors
100a and 100b connect two wiring lines 10a and 10b extending from a distribution
switchboard. The feed connectors 100c and lOOd connect the two lines extending to
another socket device at an opposite side of the distribution switchboard. The socket
connector 2 is connected to equipment and supplies power to the equipment. The
socket device 3 also includes an impedance stabilization device 110.
[0107]
As each of the source connectors 100a and 100b and the feed connectors
100c and lOOd, a quick connector, which achieves electrical connection by
sandwiching electric wire inserted as a wiring line, is preferably used.
[0108]

The source connector 100a is connected to the feed connector 100c by the
line 10a. The source connector 100b is connected to the feed connector lOOd by the
line 10b. Note that, in order to indicate that the lines 10a and 10b illustrated in FIG.
11 are respectively the same as the lines 10a and 10b illustrated in FIG. 10, the same
reference signs are assigned.
[0109]
Also, as illustrated in FIG. 11, the line 10a extends to one terminal of the
socket connector 2, and the line 10b extends to the other terminal of the socket
connector 2.
[0110]
The impedance stabilization device 110 is inserted between the terminal and
the lines 10a and 10b.
[0111]
As illustrated in FIG. 11, the impedance stabilization device 110 includes a
switch 120, a matching impedance element 130, a low-frequency blocking element
140 and an impedance upper circuit 160.
[0112]
As illustrated in FIG. 11, a circuit including the switch 120, the matching
impedance element 130 and the low-frequency blocking element 140 connected in
series is connected in parallel with the impedance upper circuit 160 to form another
circuit. The other circuit is connected to the line 10a at one end thereof, and is
connected to the line 10b at the other end thereof.
[0113]
As the matching impedance element 130, a resistance element having
resistance approximately equal to the characteristic impedance of wiring (lines 10a
and 10b) is typically used.
[0114]
Typically used as the low-frequency blocking element 140 is a capacitor

having low impedance to the high-frequency signal for use in the power line
communication, and having sufficiently high impedance to a power current such as
an alternating current of low-frequency (e.g. 50 Hz and 60 Hz) and a direct current.
[0115]
The matching impedance element 130 corresponds to the parallel matching
impedance element 13 in Embodiment 1. The low-frequency blocking element 140
corresponds to the low-frequency blocking element 14 in Embodiment 1. The
impedance upper circuit 160 performs functions of the series matching impedance
elements 11 and 12 in Embodiment 1.
[0116]
The impedance upper circuit 160 is typically realized by a choke coil. FIG.
12 illustrates an example of a configuration of the impedance upper circuit 160.
[0117]
As illustrated in FIG. 12, the impedance upper circuit 160 includes choke
coils 161a and 161b, and resistance elements 162a and 162b. As illustrated in FIG.
12, the impedance upper circuit 160 has a configuration in which a circuit including
the choke coil 161a and the resistance element 162a connected in parallel is
connected in series with the line 10a, and another circuit including the choke coil
161b and the resistance element 162b connected in parallel is connected in series
with the line 10b. By setting the impedance of the resistance elements 162a and
162b so as to be several times higher than the approximate characteristic impedance
of the lines 10a and 10b, the effect of equipment having a low impedance is reduced
when the equipment is connected to the socket connector 2, and power line
communication is enabled by passing the high-frequency signal to same extent even
when the power line communication equipment is connected to the socket connector
2. Each of the choke coils 161a and 161b corresponds to the high-frequency
blocking element in Embodiment 1. Each of the resistance elements 162a and 162b
corresponds to the series matching impedance element in Embodiment 1.

[0118]
Referring back to FIG. 11, the switch 120 included in the impedance
stabilization device 110 opens while wiring (the lines 10a and 10b) is connected to
the feed connectors 100c and lOOd, and closes while no wiring is connected to the
feed connectors 100c and lOOd.
[0119]
The switch 120 detects a voltage value at each of the feed connectors 100c
and lOOd. According to a change in voltage value, the switch 120 detects whether
wiring is connected to the feed connectors 100c and lOOd. The switch 120 performs
the detection by storing in advance a range of the voltage values in a case where
wiring is connected to the feed connectors 100c and lOOd, and determining whether
or not the detected voltage value is within the stored range. The switch 120 opens or
closes according to results of the detection.
[0120]
In a case where wiring is connected to the feed connectors 100c and lOOd,
the socket device is not the end of the power distribution system. The switch 120
opens as it is unnecessary to cause the matching impedance element 130 to function
as a termination resistor. In a case where no wiring is connected to the feed
connectors 100c and lOOd, the socket device has to be the end of the power
distribution system. The switch 120 closes as it is necessary to cause the matching
impedance element 130 to function as the termination resistor.
[0121]
With such a configuration, it is possible to provide the impedance
stabilization device that uses the same socket connector 2 as a terminal for
outputting a power current and a terminal for outputting a high-frequency signal,
reduces the impedance mismatch regardless of whether or not the socket device is
the end of the power distribution system, and is applicable to the power distribution
system having the daisy-chain configuration.

When equipment is connected to the socket connector 2, the impedance
upper circuit 160 included in the impedance stabilization device 110 reduces the
effect of the impedance of the connected equipment on the wiring side. Therefore,
the socket device 3e on the right side of FIG. 10 operates as the matched end,
whereas the socket devices 3c and 3d other than the socket device 3e operate as part
of the wiring to which no equipment is connected. With the above-mentioned
configuration, the wiring illustrated in FIG. 10 achieves the power distribution
system that does not cause intense reflection in each socket device, and that enables
the powerline communication having favorable channel characteristics.

The following describes various modifications of the impedance
stabilization device 110 in Embodiment 2. Note that differences from the impedance
stabilization device 110 are mainly described here.

An impedance stabilization device 1300 illustrated in FIG. 13 differs from
the impedance stabilization device 110 illustrated in FIG. 11 in that the matching
impedance element 130 is removed, and the impedance upper circuit 160 is inserted
at a side closer to not the socket connector 2 but the line than the switch 120 is. The
impedance upper circuit 160 has the same configuration as that illustrated in FIG. 12.
The total impedance of the two resistance elements 162a and 162b included in the
impedance upper circuit 160 is set so as to be approximately equal to the
characteristic impedance of the wiring. Since the two resistance elements 162a and
162b double as the matching impedance element 130 included in the impedance
stabilization device 110 illustrated in FIG. 11, the matching impedance element 130
is removed, and thus the circuit is simplified.

An impedance stabilization device 1400 illustrated in FIG. 14 differs from

the impedance stabilization device 110 illustrated in FIG. 11 in that an impedance
upper circuit 160a is inserted at a side closer to the line than the switch 120 is, and
an impedance upper circuit 160b is inserted at a side closer to the socket connector 2
than the switch 120 is.
[0122]
The impedance upper circuit 160a included in the impedance stabilization
device 1400 operates in a similar manner to the impedance upper circuit 160
included in the impedance stabilization device 1300 illustrated in FIG. 13. That is to
say, the total impedance of the two resistance elements 162a and 162b included in
the impedance upper circuit 160a is set so as to be approximately equal to the
characteristic impedance of the wiring. The two resistance elements 162a and 162b
double as the matching impedance element 130 illustrated in FIG. 11.
[0123]
On the other hand, while the impedance upper circuit 160b also has the
configuration as illustrated in FIG. 12, the impedance of the resistance elements
162a and 162b included in the impedance upper circuit 160b does not have to be the
same as that of the resistance elements 162a and 162b included in the impedance
upper circuit 160a. For example, in order to preferentially reduce the effect of
equipment connected to the socket connector 2, resistance of the resistance element
included in the impedance upper circuit 160b may be set so as to be higher than that
of the resistance element included in the impedance upper circuit 160a. Alternatively,
in order to reduce the loss of high-frequency signals when power line
communication equipment is connected to the socket connector 2, resistance of the
resistance element included in the impedance upper circuit 160b may be set so as to
be lower than that of the resistance element included in the impedance upper circuit
160a.
[0124]
As described above, the impedance stabilization device 1400 independently

controls a degree of the impedance mismatch and a loss of the high-frequency
signals, as the impedance upper circuit 160a controls the degree of the impedance
mismatch and the impedance upper circuit 160b controls the loss of the
high-frequency signals.

An impedance stabilization device 1500 illustrated in FIG. 15 differs from
the impedance stabilization device 110 illustrated in FIG. 11 in that a switch 120a is
added. The switch 120b included in the impedance stabilization device 1500 is
equivalent to the switch 120 of the impedance stabilization device 110.
[0125]
The switch 120a is configured to open while wiring is connected to the
source connectors 100a and 100b included in the socket device 3, and to close while
no wiring is connected to the source connectors 100a and 100b. The switch 120a
detects whether or not wiring is connected in a similar manner to the switch 120.
[0126]
The switch 120b is configured to open while wiring is connected to the feed
connectors 100c and lOOd included in the socket device 3, and to close while no
wiring is connected to the feed connectors 100c and lOOd, similarly to the switch
120.
[0127]
In the impedance stabilization device 1500, while no wiring is connected to
at least one of the source connector and the feed connector, at least one of the
switches 120a and 120b closes so that two lines 10a and 10b are connected via the
second circuit including the matching impedance element 130 and the
low-frequency blocking element 140 connected in series.
[0128]
On the other hand, while wiring is connected to each of the source
connector and the feed connector, each of the switches 120a and 120b opens. Since

the switches 120a and 120b are connected in parallel, the matching impedance
element 130 and the low-frequency blocking element 140 are not used.
[0129]
With the configuration illustrated in FIG. 15, there is no need to distinguish
the source connector and the feed connector. The socket device at the end operates
as a matching terminal and the socket device that is not at the end operates as part of
the wiring to which no equipment is connected, regardless of whether wiring is
connected to the source connector or the feed connector. Therefore, although having
a disadvantage that the number of circuits increases compared with the impedance
stabilization device having the configuration illustrated in FIG. 11 as the switch is
added, the impedance stabilization device 1500 has an advantage that it is installed
in the power distribution system more easily compared with the impedance
stabilization device having the configuration illustrated in FIG. 11.
[0130]
Note that, although the switches 120a and 120b are separately provided in
FIG. 15, the configuration of the switches 120a and 120b are not limited to this. A
single switch may mechanically be connected to each of the source connector and
the feed connector to achieve a similar function.
[0131]

Embodiment 3 describes a case where the impedance stabilization device in
Embodiment 1 is applied to the power distribution system having the daisy-chain
configuration in Embodiment 2.
[0132]
A configuration equivalent to that of the impedance stabilization device 110
or the like in Embodiment 2 is achieved as the configuration of the impedance
stabilization device la illustrated in FIG. 16 in which the switch 120 is added to the
impedance stabilization device 1.

[0133]
As illustrated in FIG. 16, the switch 120 is connected in series with the
second circuit including the parallel matching impedance element 13 and the
low-frequency blocking element 14 connected in series. FIG. 17 illustrates a
configuration of an equivalent circuit of the impedance stabilization device la
illustrated in FIG. 16 to a high-frequency signal in a case where the switch 120
closes.
[0134]
Similarly, by inserting the switch 120 into the impedance stabilization
device 50 at a position as shown in FIG. 18, it is possible to provide an impedance
stabilization device 50a having an equivalent configuration to the impedance
stabilization device 110.
[0135]
Furthermore, by inserting the switch 120 into the impedance stabilization
device 70 illustrated in FIG. 7A at a position as shown in FIG. 19, it is possible to
provide an impedance stabilization device 70a having an equivalent configuration to
the impedance stabilization device 110.
[0136]
Note that, although not shown in FIGs. 16 to 19, each switch 120 opens and
closes according to whether wiring is connected to the feed connectors 100c and
lOOd included in the socket device, similarly to the switch 120 in Embodiment 2.
[0137]
Also, as described in Modification 3 of Embodiment 2, another switch 120
that opens and closes according to whether wiring is connected to the source
connector may be connected in parallel with the switch 120 in each of the
configurations illustrated in FIGs. 16 to 19.
[0138]
Note that, in such a case, conditions that the series matching impedance

element and parallel matching impedance element should meet are the same as those
described in Embodiment 1.
< Summary of Embodiment 3>
As described above, by connecting the switch 120 in series with the second
circuit, the impedance stabilization device in Embodiment 1 is applicable to the
power distribution system having the daisy-chain configuration.
[0139]

Although the present invention has been described based on the above
embodiments, it is obvious that the present invention is not limited to the above
embodiments. The following describes further modifications of the above
embodiments of the present invention that can be made without departing from the
spirit of the present invention.
[0140]
(1) In each of the above embodiments, the impedance stabilization device is
provided to the socket. Power distribution equipment including the impedance
stabilization device, however, is not limited to the socket device. The impedance
stabilization device may be built into another type of power distribution equipment.
For example, the impedance stabilization device may be built into a joint box used at
a point where the wiring branches or connection equipment that fixes a lighting
fixture to the ceiling. Alternatively, the impedance stabilization device may be built
into a power strip used by being connected to an existing socket or may be used as
an adapter inserted between the socket and the connection equipment.
[0141]
(2) In Embodiment 2 described above, the switch 120 is configured to detect
the voltage value of each of the feed connectors 100c and lOOd. However, any
method may be used to detect whether or not wiring is connected to the feed
connectors 100c and lOOd. For example, instead of detecting the voltage value using

the switch 120, the impedance stabilization device may include a detection circuit
for detecting the voltage value at each of the feed connectors 100c and 1 OOd, and the
switch 120 may open and close according to instructions from the detection circuit.
Alternatively, another switch that switches on while wiring is connected to each of
the feed connectors 100c and lOOd may be provided, and the switch 120 may open
upon being notified that the other switch switches on.
[0142]
(3) Each of the above embodiments describes the impedance stabilization
device that is used in the power distribution system composed of two lines. The
impedance stabilization device, however, is not limited to that used in the power
distribution system composed of two lines.
[0143]
As illustrated in FIGs. 20 to 22, the impedance stabilization device is
applicable to a power distribution system composed of a plurality of lines.
[0144]
FIGs. 20 and 21 each illustrate examples of a case where the impedance
stabilization device is applied to a power distribution system composed of three lines,
namely two power lines and one ground line. FIG. 21 illustrates an example of a
configuration that is more balanced than that illustrated in FIG. 20.
[0145]
With such a configuration, it is possible to provide an impedance
stabilization device that is applicable to a high voltage power distribution system
requiring the ground wire, a single-phase three-wire power distribution system
supplying power to standard homes, or the like.
[0146]
As illustrated in FIG. 22, the number of lines may further be increased.
[0147]
The impedance stabilization device is also applicable to a three-phase

alternating-current power distribution system as illustrated in FIG. 22.
[0148]
Furthermore, a Neutral line illustrated in FIG. 22 may be a Common GND
line that applies a different voltage to each line (cpl to cp3). In such a case, the
number of lines may further be increased according to the amount of voltage
applied.
[0149]
As described above, the impedance stabilization device is applicable to a
power distribution system composed of three or more lines according to a type of
power source.
[0150]
(4) In each of the above embodiments, a passive element called the
resistance element is used as the series matching impedance element included in the
impedance stabilization device. Instead of the passive element, however, an active
element may be used as long as the conditions described in Embodiment 1 are met.
[0151]
FIG. 23 illustrates an example of an impedance stabilization device that
uses the active element as the series matching impedance element.
[0152]
A two-way buffer amplifier is used as the series matching impedance
element included in the impedance stabilization device illustrated in FIG. 23. The
two-way buffer amplifier switches between buffer amplifiers to be used according to
a communication direction (communication from the wiring side to the equipment
side or communication from the equipment side to the wiring side). The impedance
stabilization device may be configured in the above-mentioned manner.
[0153]
Note that, although the impedance stabilization device illustrated in FIG. 23
is a modification of the impedance stabilization device 50 illustrated in FIG. 5, the

active element may also be used as the series matching impedance element
illustrated in each of the embodiments.
[0154]
(5) Instead of being used in the power distribution system, the impedance
stabilization device in each of the above-mentioned embodiments may be connected
to other impedance stabilization devices to achieve branch wiring illustrated in FIG.
24. Alternatively, integral branch equipment having a configuration illustrated in
FIG. 24 may be provided. The number of branching lines is not limited to two as
illustrated in FIG. 24, and may be more than two such as three or four.
[0155]
(6) Each of the configurations described in Embodiments 1 to 3 and
may be combined with one another as long as the combined
configuration reduces the impedance mismatch and shares the signal input-output
terminal.
[Industrial Applicability]
[0156]
The impedance stabilization device pertaining to the present invention is
configured such that each of the power line communication equipment and the
household electrical appliance is detachably connected to the terminal such as a
socket, and prevents the channel characteristic degradation in the power line
communication. Therefore, the impedance stabilization device pertaining to the
present invention is useful for a home network or the like using the power line
communication.
[Reference Signs List]
[0157]
1,1a, 50, 50a, 70, 70a, 80, 110, 1300, 1400, 1500 impedance stabilization device
2, 2a, 2b socket connector
3, 3a, 3b, 3c, 3d, 3e socket device (socket, power distribution equipment)

5 distribution switchboard
10a, 10b line
11, 11a, lib, 12, 12a, 12b series matching impedance element (first impedance
element)
13 parallel matching impedance element (second impedance element)
14, 140 low-frequency blocking element
15, 15a, 15b, 15c, 15d high-frequency blocking element
18 CMC (Common Mode Choke)
100a, 100b source connector
100c, lOOd feed connector
120, 120a, 120b switch
130 matching impedance element
160, 160a, 160b impedance upper circuit
161a, 161b choke coil
162a, 162b resistance element
2501 termination resistor
2502 capacitor (condenser)
2503 inductor
2504 signal input-output terminal

GfcAiMS -
1. An impedance stabilization device used for power line communication performed
by superimposing a high-frequency signal on a power line composed of at least two
lines, the impedance stabilization device comprising:
a first circuit that includes a first impedance element and a high-frequency
blocking element connected in parallel, and is inserted into at least one of the lines;
and
a second circuit that includes a second impedance element and a
low-frequency blocking element connected in series, and via which the lines are
connected, wherein
the high-frequency blocking element has higher impedance than impedance
of the first impedance element to the high-frequency signal, and has lower
impedance than impedance of the first impedance element to one of a low-frequency
alternating current and a direct current supplied to the power line, and
the low-frequency blocking element has lower impedance than impedance
of the second impedance element to the high-frequency signal, and has higher
impedance than impedance of the second impedance element to one of the
low-frequency alternating current and the direct current.
2. The impedance stabilization device of Claim 1, wherein
the first impedance element comprises two elements connected in series,
and
one end of the second circuit is connected to a point between the two
elements.
3. The impedance stabilization device of Claim 2, wherein
the first circuit is inserted into each of the lines, so that the lines are

balanced with respect to a ground.
4. The impedance stabilization device of Claim 3, wherein
the one end of the second circuit is connected to a point between the two
elements of the first impedance element included in the first circuit inserted into one
of the lines, and
the other end of the second circuit is connected to a point between the two
elements of the first impedance element included in the first circuit inserted into
another one of the lines.
5. The impedance stabilization device of Claim 1, wherein
impedance of the first impedance element is 0.3 to 1.2 times higher than
characteristic impedance of the lines.
6. The impedance stabilization device of Claim 1, wherein
impedance of the second impedance element is 0.6 to 3 times higher than
characteristic impedance of the lines.
7. The impedance stabilization device of Claim 1 being provided in power
distribution equipment having a source connector and a feed connector, wherein
the second circuit further includes a switch connected in series with either
the second impedance element or the low-frequency blocking element, and
the switch closes while no wiring is connected to the feed connector, and
opens while wiring is connected to the feed connector.
8. The impedance stabilization device of Claim 1 being provided in power
distribution equipment having a source connector and a feed connector, wherein
the second circuit further includes a switch connected in series with either

the second impedance element or the low-frequency blocking element, and
the switch closes while no wiring is connected to at least one of the source
connector and the feed connector, and opens while wiring is connected to each of the
source connector and the feed connector.
9. An impedance stabilization device that is used for power line communication
performed by superimposing a high-frequency signal on a power line composed of
at least two lines, and is provided in power distribution equipment having a feed
connector, the impedance stabilization device comprising:
a first circuit that includes an impedance element, a low-frequency blocking
element and a switch connected in series, and via which the lines are connected; and
an impedance upper circuit that is inserted between an equipment connector
and the lines, wherein
the low-frequency blocking element has lower impedance than impedance
of the impedance element to the high-frequency signal, and has higher impedance
than impedance of the impedance element to one of a low-frequency alternating
current and a direct current supplied to the power line,
the impedance upper circuit has impedance that is equal to or higher than
characteristic impedance of the lines to the high-frequency signal, and has lower
impedance than characteristic impedance of the lines to one of the low-frequency
alternating current and the direct current, and
the switch closes while no wiring is connected to the feed connector, and
opens while wiring is connected to the feed connector.
10. The impedance stabilization device of Claim 9, wherein
at least part of the impedance upper circuit doubles as the impedance
element.

11. An impedance stabilization device that is used for power line communication
performed by superimposing a high-frequency signal on a power line composed of
at least two lines, and is provided in power distribution equipment having a source
connector and a feed connector, the impedance stabilization device comprising:
a first circuit that includes an impedance element, a low-frequency blocking
element and a switch connected in series, and via which the lines are connected; and
an impedance upper circuit that is inserted between an equipment connector
and the lines, wherein
the low-frequency blocking element has lower impedance than impedance
of the impedance element to the high-frequency signal, and has higher impedance
than impedance of the impedance element to one of a low-frequency alternating
current and a direct current supplied to the power line,
the impedance upper circuit has impedance that is equal to or higher than
characteristic impedance of the lines to the high-frequency signal, and has lower
impedance than characteristic impedance of the lines to one of the low-frequency
alternating current and the direct current, and
the switch closes while no wiring is connected to at least one of the source
connector and the feed connector, and opens while wiring is connected to each of the
source connector and the feed connector.
12. The impedance stabilization device of Claim 11, wherein
at least part of the impedance upper circuit doubles as the impedance
element.
13. An impedance stabilization device used for power line communication
performed by superimposing a high-frequency signal on a power line composed of
at least two lines, the impedance stabilization device comprising:
a first impedance element that is inserted into at least one of the lines;

a second impedance element that connects the lines;
a high-frequency blocking element that is inserted into at least one of a first
line and a second line other than the at least two lines, the first line being connected
to the at least one line into which the first impedance element is inserted so as to
bridge the first impedance element and to be in parallel with the at least one line into
which the first impedance element is inserted, the second line being connected to
another line to which the first line is not connected so as to bridge a point where the
second impedance element connects to the other line and to be in parallel with the
other line to which the first line is not connected; and
a low-frequency blocking element that connects the first and second lines,
wherein
the high-frequency blocking element has higher impedance than impedance
of the first impedance element to the high-frequency signal, and has lower
impedance than impedance of the first impedance element to one of a low-frequency
alternating current and a direct current supplied to the power line, and
the low-frequency blocking element has lower impedance than impedance
of the second impedance element to the high-frequency signal, and has higher
impedance than impedance of the second impedance element to one of the
low-frequency alternating current and the direct current.

Provided is an impedance stabilization device having a configuration in
which a circuit including a series matching impedance element (11a and 12a (11b
and 12b)) and a high-frequency blocking element connected in parallel is inserted in
series into at least one of lines (10a (10b)) constituting a power line, and the lines
(10a and 10b) are connected via another circuit including a parallel matching
impedance element (13) and a low-frequency matching element (14) connected in
series. A high-frequency signal passes through the series matching impedance
element, a power current passes through the high-frequency blocking element, and
the parallel matching impedance element functions as a termination resistor when a
terminal on an equipment side is an open end.