Abstract:
A power line communication apparatus includes a power plug configured to connect to a power line, and a power plug receiver configured to connect to the power plug. The power line communication apparatus also includes a power line communicator configured to receive a signal transmitted through the power line, and a power supplier configured to generate power based on power received from the power plug and supply the generated power to the power line communication apparatus. The power line communication apparatus further includes a power board on which the power plug receiver is mounted, and a heat radiator that connects to the power line communicator and radiates heat generated from the power line communicator, wherein a portion of the heat radiator overlaps a portion of the power board when viewed perpendicular to the power board, and the portion of the power board does not include the power plug receiver.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/854,384 filed Apr. 1, 2013 which is a continuation of U.S. patent application Ser. No. 12/182,200, filed Jul. 30, 2008, now U.S. Pat. No. 8,411,451 issued Apr. 2, 2013, the content of which are expressly incorporated herein by reference in their entireties. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a power line communication apparatus capable of performing communication employing a power line as a transmission medium. 
         [0004]    2. Background Art 
         [0005]    Recently, there has been suggested a power line communication system capable of transmitting data by superposing a high-frequency signal on a power line carrying electric power such as commercial power. As such a type of a power line communication system, there is known a multi-carrier transmission communication apparatus capable of transmitting and receiving a multi-carrier communication signal (for example, see JP-A-2003-218831). 
         [0006]    The power line communication apparatus such as a PLC (Power Line Communication) modem used in the power line communication system can be realized into various types such as an AC adapter type directly connected to an outlet of a power line, a single modem type having a function of a hub, a router, or the like, and an apparatus-integrated type integrated into a PC (Personal Computer) or the like. Accordingly, if a signal processor of the PLC modem is designed in accordance with a type of respective apparatus, design cost or manufacture cost may be increased that much. 
         [0007]    An analog signal processor of the PLC modem has a problem in that when the analog signal processor is apart from a coupler which separates and couples a high frequency signal for the power line communication from and with the power line, noise may increase in the analog high frequency signal (communication signal of the power line), thereby deteriorating a communication performance. Meanwhile, it is preferable that the analog signal processor of the PLC modem and a network interface unit such as Ethernet (registered trademark) provided in the subsequent step of the PLC modem are apart from each other as much as possible. 
         [0008]    For that reason, various units such as a power supply unit, a signal processor, and an interface unit are necessary to be arranged in consideration of various circumstances of the power line communication apparatus. 
       SUMMARY 
       [0009]    According to an aspect of the invention, there is provided a communication apparatus which performs communication through a power line and a transmission medium different from the power line. The communication apparatus includes: a power board which is provided with a power unit connected to the power line; an interface board which is separately formed from the power board and is provided with an interface for performing communication through the transmission medium; and a communication board which is separately formed from the power board and the interface board and is provided with a power line communication unit for performing communication through the power line and a connection unit electrically connectable to the power board and the interface board. 
         [0010]    According to the invention, there is provided a communication apparatus capable of configuring a communication board provided with a signal processor for power line communication which can be in common even in various types of an apparatus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The above advantage of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein like reference numerals designate like or corresponding parts throughout the several views, and wherein: 
           [0012]      FIG. 1  is a perspective view illustrating an arrangement configuration of major elements of a communication apparatus; 
           [0013]      FIG. 2  is a perspective view illustrating a configuration of each board of the communication apparatus; 
           [0014]      FIG. 3A  is perspective view illustrating the assembly process of each unit of the communication apparatus; 
           [0015]      FIG. 3B  is a perspective view illustrating the assembly of the upper casing; 
           [0016]      FIG. 3C  is a perspective view illustrating the assembly of the upper casing and the lower casing; 
           [0017]      FIG. 4  is block diagram illustrating an example of a circuit configuration of the communication apparatus; 
           [0018]      FIG. 5  is a perspective view illustrating an arrangement configuration of the major elements of the communication apparatus; 
           [0019]      FIG. 6  is a perspective view illustrating an arrangement configuration of the major elements of the communication apparatus; 
           [0020]      FIG. 7  is a perspective view illustrating an arrangement configuration of the major elements of the communication apparatus; 
           [0021]      FIG. 8  is a perspective view illustrating an arrangement configuration of the major elements of the communication apparatus; and 
           [0022]      FIG. 9  is a perspective view illustrating an arrangement configuration of the major elements of the communication apparatus. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  shows a configuration example of an AC adapter-typed PLC modem directly connected to an outlet of a power line. The configuration of the communication apparatus is not limited thereto, but may be modified in various forms. 
         [0024]    In a PLC modem  10 , a power plug  25  is integrally formed on one outer surface of a lower casing  100  so as to protrude therefrom. The PLC modem  10  is of an AC adapter-type which is directly connected to an outlet of the power line. A power board  101  on which a power unit is formed, a communication board  102  on which a signal processor for power line communication is formed, and an interface board  103  on which a network interface unit of an Ethernet (registered trademark) are housed within the lower casing  100 . 
         [0025]    Three boards are arranged in such a manner that the power board  101  and the interface board  103  are connected through a power connector  104  to be arranged on one plane and that the communication board  102 , which is separately formed from the power board  101  and the interface board  103 , is erected to the power board  101  and the interface board  103  at a substantially right angle. In addition, the communication board  102  is electrically connected to the power board  101  and the interface board  103  through a first connector (PLC connector)  105  and a second connector (interface connector)  106 , respectively. 
         [0026]    The communication board  102  is fixed to a board holding frame  107 A of a heat radiator  107  formed by curving a plate-shaped member such as a metal plate or the like using a screw or the like, and is connected to the power board  101  and the interface board  103  through the first connector  105  and the second connector  106 , respectively. In addition, the heat radiator  107  is attached and fixed to the lower casing  100  along with the interface board  103  by a screw or the like in a fixing portion  107 B in a state where the heat radiator  107  holds and fixes the communication board  102  to be integrally formed with the power board  101  and the interface board  103 . 
         [0027]    In  FIG. 2 , the heat radiator  107  is omitted and the power board  101 , the communication board  102 , and the interface board  103  are shown for convenient explanation. 
         [0028]    On the power board  101 , a plug receiver  111  of a power plug  25 , a coil transformer  16 A and coupling capacitors  16 B and  16 C of the coupler  16 , one part of the power connector  104 , one part of the first connector  105 , and the like are mounted as major components. On the interface board  103 , the other part of the power connector  104 , one part of the second connector  106 , a network connection unit  112  housing four modular jacks for network connection, and the like are mounted as major components. On the communication board  102 , the other part of the first connector  105 , the other part of the second connector  106 , a circuit IC (not shown), and the like are mounted as major components. At this time, the first connector  105  and the second connector  106  are positioned at both ends in a longitudinal direction of the communication board  102  to be apart from each other. The first connector  105  which serves as a PLC connector includes a connection portion of a transmission path through which a high frequency analog signal (PLC signal) for PLC is transmitted. The second connector  106  which serves as an interface connector includes a connection portion of a transmission path through which a digital signal containing data, which is transmitted to and received from another apparatus through a network interface or the like. 
         [0029]    As shown in  FIG. 3A , the power board  101 , the interface board  103 , the communication board  102 , and the heat radiator  107  are integrally assembled to be connected to each other. At this time, a base end of the power plug  25  is inserted into the plug receiver  111  of the power board  101 , and the power board  101 , the interface board  103 , and the heat radiator  107  are fixed to the lower casing  100  using a screw. Boss formed at predetermined positions of the lower casing  100  engage with boss holes of the power board  101  and the interface board  103 , so that the boards are positioned on the lower casing  100 . 
         [0030]    Subsequently, as shown in  FIG. 3B , the boards positioned on the lower casing  100  are covered with an upper casing  110 . As shown in  FIG. 3C , the lower casing  100  and the upper casing  110  are fixed to each other by screws. In the PLC modem  10  assembled in this way, the power plug  15  and the network connection unit  112  are exposed outside. In addition, the power plug  25  is configured so as to be connected to an outlet of a power line and the network connection unit  112  is configured so as to be connected to a network cable. Electric power is supplied through the power line and the PLC signal is received and transmitted, so that the PLC modem  10  enables data communication to be performed by transmitting data to another apparatus such as a PC through the network cable. 
         [0031]    As described above, the PLC modem  10  includes the power board  101 , the communication board  102 , and the interface board  103 . As shown in  FIG. 4 , the power board  101  is provided with the power plug  25 , the coupler  16 , an impedance upper  27 , an AC/DC converter  24 , and switching power supply  20 . The switching power supply  20  supplies various direct-current voltages (for example, +1.2 V, +3.3 V, +10.5 V, and +12 V) to the communication board  102  or the interface board  103 . The switching power supply  20  includes, for example, a switching transformer and a DC-DC converter (which are all not shown). The electric power is supplied from the power plug  25  to the switching power supply  20  through the impedance upper  27  and AC/DC converter  24 . The coupler  16  separates and couples the PLC signal, which is a high frequency signal, from and to the power line and includes the coil transformer  16 A and the coupling capacitors  16 B and  16 C. The coupling capacitors  16 B and  16 C are connected to the power plug  25 , and the coil transformer  16 A is connected to the communication board  102 . 
         [0032]    The communication board  102  is provided with a main IC (Integrated Circuit)  11 , an AFE/IC (Analog Front END/Integrated Circuit)  12 , a low-pass filter (LPF)  13 , a driver IC  15 , and a band-pass filter (BPF)  17 , a memory  18 , and an Ethernet PHY/IC (Physical layer/Integrated Circuit)  19 . An indicator  23  is connected to the main IC  11 . The main IC  11  functions as a communication control unit in power line communication. 
         [0033]    The main IC  11  includes a CPU (Central Processing Unit)  11 A, a PLC/MAC (Power Line Communication/Media Access Control layer) block  11  C, and a PLC/PHY (Power Line Communication/Physical layer) block  11  B. A 32-bit RISC (Reduced Instruction Set Computer) processor is mounted in the CPU  11 k The PLC/MAC block  11 C manages a MAC layer (Media Access Control layer) of a transmission signal and a reception signal. The PLC/PHY block  11 B manages a PHY layer (Physical layer) of a transmission signal and a reception signal. The AFE/IC  12  includes a DA converter (DAC: D/A converter)  12 A, an AD converter (ADC: A/D converter)  12 D, and variable gain amplifiers (VGA: Variable Gain Amplifier)  12 B and  12 C. In addition, the CPU  11 A controls operations of the PLC/MAC block  11 C and the PLC/PHY block  118  using data stored in the memory  18  and also controls the PLC modem  10  as a whole. 
         [0034]    The interface board  103  is provided with a hub  28 , an indicator  29 , and the network connection unit  112  housing four RJ45 type modular jacks  22 A,  22 B,  22 C, and  22 D. Network cables for making connection to a PC or like are connected to the modular jacks  22 A,  22 B,  22 C, and  22 D. 
         [0035]    Communication by means of the PLC modem  10  in  FIG. 4  is performed as follows. That is, data input to the modular jacks  22 A,  22 B,  22 C, and  22 D is transmitted to the main IC  11  through the hub  28  and the Ethernet PHY/IC  19 , and a digital transmission signal is generated by performing a digital signal process. The generated digital transmission signal is converted into an analog signal by the DA converter (DAC)  12 A of the AFE/IC  12  and superposed on a transmission path as the PLC signal through the low-pass filter  13 , the driver IC  15 , and the coupler  16  to be output to a power line  1 A through the power plug  25  and an outlet  2 . 
         [0036]    The signal received from the power line  1 A is separated as the PLC signal via the coupler  16 , its gain is adjusted by the variable gain amplifier (VGA)  12 C of the AFE/IC  12  through the band-pass filter  17 , and the signal is converted into a digital signal by the AD converter (ADC)  12 D. The converted digital signal is transmitted to the main IC  11  and subjected to a digital signal process to be converted into digital data. The converted digital data is output from the modular jacks  22 A,  22 B,  22 C, and  22 D through the Ethernet PHY/IC  19  and the hub  28 . 
         [0037]    The PLC modem  10  is configured in such a manner that the power board  101  is a separate body from the communication board  102 , and thus the communication board  102  is separately provided to be connected to the power board  101  through the connector. In this way, the communication board  102  provided with the signal processor for power line communication can be used in common in various apparatuses. Accordingly, when a power line communication function is provided to various apparatuses, the communication board  102  can be used in common. Therefore, since it is not necessary to design a separate communication board in accordance with the shape of various apparatuses, design cost or manufacture cost can be reduced. 
         [0038]    The first connector  105  and the second connector  106  are separately provided in the communication board  102 . The first connector  105  is apart from the second connector  106 . The coupler  16  is disposed in the vicinity of the first connector  105  and the power board  101 , and an input unit (analog signal processor) for the PLC signal formed on the communication board  102  can be connected to the coupler  16  through the first connector  105  at a location where they are as close as possible. Accordingly, it is possible to shorten the transmission path for an analog signal. Moreover, the communication board  102  can come closer to the coupler  16  by configuring the communication board  102  to be erect with respect to the power board  101 . Furthermore, since the communication board  102  and the interface board  103  can be connected to each other through the second connector  106  at a location which is away from the first connector  105 , a transmission path for a digital signal containing data transmitted to and received from a network connector such as the Ethernet (registered trademark) which is an interface of another apparatus can be apart from the analog signal processor or a transmission path for an analog signal. With such a configuration, interference of noise can be reduced, thereby improving a communication performance. 
         [0039]    The power board  101  and the interface board  103  may be configured as two separate boards, and may be also configured as one integrated board like a base board. When the power board  101  and the interface board  103  are configured as the one board, the number of components is reduced. When the power board  101  and the interface board  103  are configured as the two boards, the interface board  103  can be exchanged with a different board having a different shape of the network connection unit  112  or the like. Accordingly, it is possible to configure the PLC modem to easily correspond to the different number of connection ports, various network types, and the like. 
         [0040]    The heat radiator  107  is formed by curving a plate-shaped member such as a metal plate having high thermal conductivity and electrical conductivity, and holds the communication board  102  so as to be housed and fixed to the casing. With such a configuration, it is possible to maintain strength while ensuring sufficient heat radiating capacity and heat radiating area. The heat radiator  107  extends so that at least a part thereof face the power board  101  and is provided so as not to overlap with the power plug  25  and the plug receiver  111 . 
         [0041]    A support portion  107 D formed to be erected from the interface board  103  is disposed in the vicinity of an end portion  107 C of an extension portion facing the power board  101  of the heat radiator  107 . With such a configuration, even though stress is applied to the heat radiator  107  toward the power board  101 , the end portion  107 C is held by the support portion  107 D, so that displacement of the heat radiator  107  toward the power board  101  is regulated. At this time, a space between the heat radiator  107  and the power plug  25  or the plug receiver  111  is sufficiently ensured. As a modified example of the heat radiator  107 , the heat radiator  107  may be formed in a substantially reverse U shape with respect to the power board  101  and the interface board  103  so that displacement of the heat radiator toward the power board is suppressed. By configuring the heat radiator  107  in this manner, it is possible to preventing contact with the power plug  25  and the like while having a sufficient heat radiating function. 
         [0042]    Hereinafter, other embodiments regarding to arrangement of the power board  101 , the communication board  102 , and the interface board  103  will be described with reference to  FIGS. 5 to 9 . 
         [0043]    As shown in  FIG. 5 , the communication board  102  is disposed so that a direction of a normal line of the communication board  102  is different from a direction of a normal line of the power board  101  and a direction of a normal line of the interface board  103 . In addition, the communication board  102 , the power board  101 , and the interface board  103  are electrically connected to each other. The power board  101  and the interface board  103  are arranged on one plane. In addition, the power board  102  is disposed to be erect at a substantially right angle with respect to the power board  101  and the interface board  103  arranged on one plane. 
         [0044]    It is possible to allow the outer size of the upper casing  110  for housing the boards to be small by arranging the power board  101  and the interface board  103  on one plane, thereby downsizing the PLC modem  10 . Moreover, it is possible to ensure a sufficient space for mounting electronic components on the power board  101  and the interface board  103 , by disposing the power board  102  to be erect at the substantially right angle with respect to the power board  101  and the interface board  103  arranged on one plane. In particular, such a configuration is appropriate in mounting electronic components since many large-sized electronic components (for example, the coil transformer  16 A of the coupler  16  or the coupling capacitors  16 B and  16 C) can be mounted on the power board  101 . 
         [0045]    In  FIG. 5 , a longitudinal direction of the communication board  102  is substantially parallel to a transverse direction of the power board  101  and a transverse direction of the interface board  103 . 
         [0046]    The power board  101 , the interface board  103 , and the communication board  102  are electrically connected to each other through a connector  108 . The connector  108  has functions of the power connector  104 , the first connector  105 , and the second connector  106  described above. 
         [0047]    By allowing the connector  108  to have the functions of the power connector  104 , the first connector  105 , and the second connector  106 , it is possible to reduce the number of components used in the PLC modem  10 , thereby simplifying a manufacture process of the PLC modem  10 . 
         [0048]    However, the PLC signal is much influenced by noise occurring from a digital signal for an interface, since the connector  108  has the functions of the first connector  105  and the second connector  106 . For that reason, in the connector  108 , it is preferable that an insulating member (not shown) is disposed around the transmission path for transmitting the PLC signal. 
         [0049]    It is preferable that the coupler  16  (not shown) is disposed in the vicinity of the connector  108 . Since a transmission path for the PLC signal between the coupler  16  and the connector  108  can be shortened by disposing the coupler  16  in the vicinity of the connector  108 , it is possible to improve a communication performance of the PLC modem  10 . 
         [0050]    Like the configuration shown in  FIG. 5 , a configuration of major components of the PLC modem  10  shown in  FIG. 6  is as follows. That is, a direction of a normal line of the communication board  102  is different from a direction of a normal line of the power board  101  and a direction of a normal line of the interface board  103 . In addition, the communication board  102 , the power board  101 , and the interface board  103  are electrically connected to each other. 
         [0051]    The power board  101  and the interface board  103  are arranged on one plane. In addition, the power board  102  is disposed to be erect at a substantially right angle with respect to the power board  101  and the interface board  103  arranged on one plane, and is disposed between the power board  101  and the interface board  103 . 
         [0052]    In the configuration example shown in  FIG. 6 , since the communication board  102  is disposed between the power board  101  and the interface board  103 , an area where the communication board  102  overlaps with the power board  101  and the interface board  103  can be made small. Accordingly, such a configuration is appropriate in mounting electronic components since a large area where electronic components are mounted in the power board  101  and the interface board  103  and the interface board  103  can be ensured. 
         [0053]    Moreover, like the configuration example shown in  FIG. 5 , since the power board  102  is disposed to be erect at the substantially right angle with respect to the power board  101  and the interface board  103  arranged on one plane, a large area where electronic components are mounted in the power board  101  and the interface board  103  can be ensured. In particular, such a configuration is appropriate in mounting electronic components since many large-sized electronic components (for example, the coil transformer  16 A of the coupler  16  or the coupling capacitors  16 B and  16 C) can be mounted on the power board  101 . 
         [0054]    In  FIG. 6 , a longitudinal direction of the communication board  102  is substantially parallel to a longitudinal direction of the power board  101  and a longitudinal direction of the interface board  103 . 
         [0055]    The first connector  105  is provided on one main surface of the communication board  102  and the second connector  106  is provided on the other main surface thereof. The first connector  105  and the second connector  106  can be located at any location of the communication board  102 , but it is preferable that the first connector  105  and the second connector  106  is disposed so as to be spaced from each other. Since an influence of noise occurring from the digital signal of an interface for receiving the PLC signal can be reduced by spacing the first connector  105  and the second connector  106 , it is possible to improve a communication performance of the PLC modem  10 . In case where the first connector  105  and the second connector  106  cannot be arranged to be separated from each other, an insulating member (not shown) may be provided at any location of the communication board  102 . 
         [0056]    In  FIG. 6 , electrical power is supplied from the power board  101  to the interface board  103  through the first connector  105  and the second connector  106 . 
         [0057]    In addition, it is preferable that the coupler  16  (not shown) is disposed in the vicinity of the first connector  105 . Since a transmission path for the PLC signal between the coupler  16  and the first connector  105  can be shortened by disposing the coupler  16  in the vicinity of the first connector  105 , it is possible to improve a communication performance of the PLC modem  10 . 
         [0058]    In  FIG. 7 , the communication board  102 , the power board  101 , and the interface board  103  are arranged so that a direction of a normal line of the communication board  102 , a direction of a normal line of the power board  101 , and a direction of a normal line of the interface board  103  are substantially parallel to each other. That is, the communication board  102 , the power board  101 , and the interface board  103  are arranged on substantially one plane. 
         [0059]    Since an outer size (size in the direction of the normal lines of the communication board  102 , the power board  101 , and the interface board  103 ) of the upper casing  110  can be made small by arranging all the boards on substantially one plane, such a configuration is appropriate in allowing the PLC modem  10  to be thin. 
         [0060]    Since the electronic components mounted on the boards can be prevented from interfering one another by arranging all the boards on substantially one plane even in a case of applying a stress to the PLC modem  10 , it is possible to improve durability or safety of the PLC modem  10 . 
         [0061]    In the configuration example shown in  FIG. 7 , since the communication board  102  is arranged between the power board  101  and the interface board  103 , an area where the communication board  102  overlaps with the power board  101  and the interface board  103  can be made equal to the area shown in  FIG. 6 . Accordingly, since a large area where electronic components are mounted on the power board  101  and the interface board  103  can be ensured, such a configuration is appropriate in mounting the electronic components. 
         [0062]    In  FIG. 7 , a longitudinal direction of the communication board  102  is substantially parallel to a longitudinal direction of the power board  101  and a longitudinal direction of the interface board  103 . 
         [0063]    The first connector  105  is provided on one long side of the communication board  102  and the second connector  106  is provided on the other long side thereof. 
         [0064]    The first connector  105  and the second connector  106  can be provided at any location, but it is preferable that the first connector  105  and the second connector  106  are provided to be apart from each other. Since the PLC signal and a digital signal for an interface can be separated one another by spacing the first connector  105  and the second connector  106  from each other, it is possible to reduce a noise influence of the digital signal on the PLC signal. 
         [0065]    In  FIG. 7 , electric power is also supplied from the power board  101  to the interface board  103  through the first connector  105  and the second connector  106 , like the configuration example shown in  FIG. 6 . 
         [0066]    It is preferable that the coupler  16  (not shown) is disposed in the vicinity of the first connector  105 . Since a transmission path for the PLC signal between the coupler  16  and the first connector  105  can be shortened by disposing the coupler  16  in the vicinity of the first connector  105 , it is possible to improve the communication performance of the PLC modem  10 . 
         [0067]    In a configuration example shown in  FIG. 8 , the communication board  102 , the power board  101 , and the interface board  103  are arranged so that a direction of a normal line of the communication board  102 , a direction of a normal line of the power board  101 , and a direction of a normal line of the interface board  103  are substantially parallel to each other, like the configuration example shown in  FIG. 7 . That is, the communication board  102 , the power board  101 , and the interface board  103  are arranged on substantially one plane. 
         [0068]    As shown in  FIG. 8 , a longitudinal direction of the communication board  102  is substantially perpendicular to a longitudinal direction of the power board  101  and a longitudinal direction of the interface board  103 . 
         [0069]    Since an outer size (size in the direction of the normal lines of the communication board  102  and the like) of the upper casing  110  can be made small by arranging all the boards on substantially one plane, such a configuration is appropriate in allowing the PLC modem  10  to be thin. 
         [0070]    Since the electronic components mounted on the boards can be prevented from interfering one another by arranging all the boards on substantially one plane even in a case of applying a stress to the PLC modem  10 , it is possible to improve durability or safety of the PLC modem  10 . 
         [0071]    The first connector  105  and the second connector  106  are provided on one long side of the communication board  102 . 
         [0072]    The first connector  105  and the second connector  106  can be provided at any location of the one long side of the communication board  102 , but it is preferable that the first connector  105  is apart from the second connector  106 . Since the PLC signal and a digital signal for an interface can be separated one another by spacing the first connector  105  and the second connector  106  from each other, it is possible to reduce a noise influence of the digital signal on the PLC signal. 
         [0073]    It is preferable that the coupler  16  (not shown) is disposed in the vicinity of the first connector  105 . Since a transmission path for the PLC signal between the coupler  16  and the first connector  105  can be shortened by disposing the coupler  16  in the vicinity of the first connector  105 , it is possible to improve the communication performance of the PLC modem  10 . 
         [0074]    Like the configuration example shown in  FIG. 5 , the communication board  102 , the power board  101 , and the interface board  103  may be connected to each other through the connector  108 . 
         [0075]    It is preferable that the coupler  16  (not shown) is disposed in the vicinity of the first connector  105 . Since a transmission path for the PLC signal between the coupler  16  and the first connector  105  can be shortened by disposing the coupler  16  in the vicinity of the first connector  105 , it is possible to improve the communication performance of the PLC modem  10 . 
         [0076]    In a configuration example shown in  FIG. 9 , the communication board  102 , the power board  101 , and the interface board  103  are arranged so that a direction of a normal line of the communication board  102 , a direction of a normal line of the power board  101 , and a direction of a normal line of the interface board  103  are substantially parallel to each other, and the communication board  102  overlaps with the power board  101  and the interface board  103 . 
         [0077]    Since outer size of the upper casing  110  and the lower casing  100  can be made small by overlapping the communication board  102  with the power board  101  and the interface board  103 , such a configuration is advantageous in miniaturization of the PLC modem  10 . 
         [0078]    The first connector  105  and the second connector  106  can be provided at any location of the edge of the communication board  102 , but it is preferable that the first connector  105  and the second connector  106  are provided on a short side of the communication board  102  like the configuration example shown in  FIG. 9 . With such a configuration, since the first connector  105  can be disposed apart from the second connector  106 , it is possible to reduce a noise influence of a digital signal for an interface on the PLC signal. 
         [0079]    Electric power is supplied from the power board  101  to the interface board  103  through the first connector  105  and the second connector  106 . 
         [0080]    Since description regarding to components mounted on the power board  101 , the communication board  102 , and the interface board  103  in  FIGS. 5 to 9  is the same as that in  FIGS. 1 to 4 , the repetitive description is omitted. 
         [0081]    It is preferable that the coupler  16  (not shown) is disposed in the vicinity of the first connector  105 . Since a transmission path for the PLC signal between the coupler  16  and the first connector  105  can be shortened by disposing the coupler  16  in the vicinity of the first connector  105 , it is possible to improve the communication performance of the PLC modem  10 . 
         [0082]    Specifically, the vicinity of the first connector  105  refers to a range of a 2 cm radius from the first connector  105  in the description of the coupler  16 . 
         [0083]    In this way, the communication board  102  can be configured so as to be used in common in other apparatuses. With such a configuration, it is possible to improve the communication performance by shortening the transmission path of an analog signal, since the analog signal processor of the communication board  102  can be disposed in the vicinity of the coupler  16 . Moreover, it is possible to improve the communication performance by reducing the noise interference, since the analog signal processor provided on the communication board  102  and the network interface unit provided on the interface board  103  can be separated from each other. Furthermore, it is possible to prevent the heat radiator  107  from coming in contact with the input unit of the power line such as the power plug  25  and the plug receiver  111  while ensuring a sufficient heat releasing function of the heat radiator  107 . 
         [0084]    As for the interface unit, an interface for wireless communication or an interface for a coaxial cable may be used. 
         [0085]    The invention is not limited to the above-described embodiments, but may be modified and applied in various forms by a person skilled in the art without departing the specification and on the basis of known techniques. Therefore, it can be understood that the various forms are included in the range of the invention.