Abstract:
A surge protected broadband power line communication system is provided. The system includes a local module with a base unit and a remote module with an extension unit. Both modules include broadband surge suppressors adapted to be connected to an AC power line. The base and extension units are connected to the surge suppressors and transmit and receive broadband digital signals through the surge suppressors and over the AC power line. The local and remote modules also have RF isolator filters connected to the surge suppressors and surge protected AC outlets connected to the outputs of the isolator filters. The local module is connected to a source of broadband digital signals such as a cable modem. The system makes the cable modem available in every room in a home simply by plugging an extension unit into an outlet located in that room.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to an AC power line communication system. More particularly, the invention relates to a surge protected broadband AC power line communication system which is able to distribute broadband digital signals over the AC power lines in a home while protecting the system from overvoltage conditions on the AC power lines.  
       BACKGROUND OF THE INVENTION  
       [0002]     Power line communication systems are known in the art. These communication systems are used, for example, to facilitate telephonic communications in locations where little or no availability exists for dedicated telephone wires. At least one such system is known which incorporates limited overvoltage protection for AC outlets.  
         [0003]     U.S. Pat. No. 6,055,435 provides a power line communication system for transmitting telephone signals over the AC power lines in a home. While the system provides surge protected AC outlets, the system does not provide surge protection for the base or extension units which incorporate the sensitive electronics for transmitting and receiving the telephone signals over the AC power lines. The surge suppressor shown in FIG. 4 of U.S. Pat. No. 6,055,435 employs high capacitance MOVs which would attenuate the RF signals on the AC power lines. As a result, the surge suppressor must be isolated from the base and extension units and AC power lines and cannot provide surge protection for the base and extension units. See FIG. 1 and column 3, lines 20-25.  
         [0004]     Wireless broadband communication systems are also known. These systems are commonly referred to as “Wi-Fi.” They employ a wireless router connected to a cable modem and allow persons within the operating range of the router to access the internet from their computers. A problem exists with Wi-Fi in that criminals are now gaining access to unsecured Wi-Fi networks. This problem was the subject of a front page article in the Mar. 19, 2005 issue of The New York Times entitled “Growth of Wireless Internet Opens New Path for Thieves.” See pages A1 and A10.  
       SUMMARY OF THE INVENTION  
       [0005]     A need exists for a system which is capable of transmitting and receiving broadband digital information securely on AC power lines while, at the same time, providing overvoltage protection for the sensitive electronic components of that system.  
         [0006]     It is an object of the present invention to provide a surge protected broadband power line communication system which does not suffer from the security defects of Wi-Fi.  
         [0007]     It is also an object of the invention to provide a broadband power line communication system which provides overvoltage protection for the sensitive electronics in the base and extension units.  
         [0008]     It is a further object of the invention to provide a broadband surge suppressor which is capable of providing overvoltage protection for the sensitive electronics in the base and extension units without significantly attenuating the RF signals being transmitted and received by those units through the broadband surge suppressor and over the AC power lines.  
         [0009]     It is a still further object of the invention to provide a broadband power line communication system with surge protected AC outlets which are isolated from the RF signals on the AC power lines while, at the same time, providing overvoltage protection for the sensitive electronics in the base and extension units.  
         [0010]     The present invention overcomes the above-mentioned problems and other limitations of the background and prior art and achieves the above-mentioned objectives by providing a surge protected broadband power line communication system that comprises a local module with a base unit and a remote module with an extension unit. Both modules include broadband surge suppressors adapted to be connected to an AC power line. The base and extension units are connected to the surge suppressors and transmit and receive broadband digital signals through the surge suppressors and over the AC power line. The local and remote modules also have RF isolator filters connected to the surge suppressors and surge protected AC outlets connected to the outputs of the isolator filters.  
         [0011]     It will be appreciated by those skilled in the art that the foregoing brief description and the following detailed description are exemplary and explanatory of this invention, but are not intended to be restrictive thereof or limiting of the advantages which can be achieved by this invention. Thus, the accompanying drawings, referred to herein and constituting a part hereof, illustrate preferred embodiments of this invention, and, together with the detailed description, serve to explain the principles of this invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Additional aspects, features, and advantages of the invention, both as to its structure and operation, will be understood and will become more readily apparent when the invention is considered in the light of the following description made in conjunction with the accompanying drawings, wherein:  
         [0013]      FIG. 1  is a functional block diagram of an embodiment of the surge protected broadband power line communication system of the present invention.  
         [0014]      FIG. 2  is a schematic diagram of an embodiment of the broadband surge suppressor portion of the present invention.  
         [0015]      FIG. 3  is a schematic diagram of an embodiment of the RF isolator filter portion of the present invention.  
         [0016]      FIG. 4  is a functional block diagram of an embodiment of the base and extension units of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     The surge protected broadband power line communication system of the present invention is shown in block diagram form in  FIG. 1 . The invention utilizes local module  10  and remote module  12 . These modules are preferably plugged into AC outlets  14  and  16 , respectively, (although they could be hard wired) and communicate with each other over AC power line  18  located, for example, within a home. Local module  10  includes broadband surge suppressor  22  which is adapted to be electrically connected to the AC power line by, for example, outlet  14 . Remote module  12  contains an identical broadband surge suppressor  32  adapted to be electrically connected to the AC power line by, for example, outlet  16 . In local unit  10 , base unit  20  and RF isolator filter  24  are both electrically connected to surge suppressor  22 . In remote unit  12 , extension unit  30  and RF isolation filter  34  are both electrically connected to surge suppressor  32 . The base and extension units may be identical and the RF isolator filters may be identical. In local unit  10  and in remote unit  12 , electrical outlets  26  and  36  are connected to RF isolator filters  24  and  34 , respectively. The RF isolator filters block the RF signals on the AC power lines from appearing at the surge protected AC outlets in the local and remote modules.  
         [0018]     The base unit may be connected (e.g. by an RJ 45 jack) to a source of broadband digital signals such as a cable modem, or a satellite TV antenna or voice over intent protocol (VoIP) signals. The extension unit may be connected (e.g. by an RJ 45 jack) to devices which utilize broadband digital signals such as a computer or a TV set top box. The system of the present invention effectively provides an internal ethernet connection over AC power line  18 . It is significant that, in the system shown in  FIG. 1 , the RF signals produced by the base and extension units are transmitted through the surge suppressors and over the AC power line. This is possible because the surge suppressor is a low capacitance (broadband) device. As a result, the surge suppressors can also provide overvoltage protection for the sensitive electronics in the base and extension units.  
         [0019]      FIG. 2  is a schematic diagram of the broadband surge suppressor portion of the preferred embodiment of the present invention. The surge suppressor has three sections: (1) a first section which detects the presence or absence of the ground; (2) a second section which provides the actual surge protection; and (3) a third section comprising an ON/OFF switch with an indicator which provides a visual indication when the power is on. In the first section, the ground is detected by transistor  48  which is turned on when the ground is present, causing green LED  44  to be illuminated. If the ground is missing, transistor  48  will be off and red LED  53  will be illuminated, alerting the user to the fact that the ground is missing.  
         [0020]     Surge protection is provided by a three electrode gas discharge tube  68  in combination with metal oxide varistors (MOVs)  64 ,  66 ,  70  and  72 . The gas discharge tube (GDT) presents a very high impedance to RF signals on the AC power lines because the GDT has very low capacitance. This is in contrast to MOVs, which have significantly higher capacitance and would, in the absence of the GDT, attenuate the RF signals on the AC power lines. The surge protection circuit shown in  FIG. 2  has one GDT electrode pair (a, b) electrically connected between AC line and AC neutral, a second GDT electrode pair (a, c) electrically connected between AC line and ground, and a third GDT electrode pair (b, c) electrically connected between AC neutral and ground. Although the preferred embodiment uses a single three electrode GDT to provide the three GDT electrode pairs, persons skilled in the art will readily appreciate that three two electrode GDTs could be used to provide the three GDT electrode pairs and that such an arrangement would be equivalent to using a single three electrode GDT. If three two electrode GDTs were used, one GDT would be electrically connected between AC line and AC neutral, one GDT would be connected between AC line and ground and one GDT would be connected between AC neutral and ground. Whether a single three electrode GDT is used or whether three two electrode GDTs are used there would be one GDT electrode pair electrically connected between AC line and AC neutral, one GDT electrode pair connected between AC line and ground and one GDT electrode pair connected between AC neutral and ground. In addition to GDT  68 , surge protection is provided by MOVs  64 ,  66  which are connected between AC line and GDT  68 , and by MOVs  70 ,  72 , which are connected between GDT  68  and ground. Thermal overload protection is provided by thermal cutouts  60 ,  62 ,  74  and  76 . In the preferred embodiment, GDT  68  has a breakdown voltage between 200 and 300 volts, while MOVs  64 ,  66 ,  70  and  72  have a breakdown voltage of on the order of 90 volts.  
         [0021]      FIG. 3  is a schematic diagram of the RF isolator filter. It comprises inductors  90  and  92  and capacitor  94 . These components form a low pass filter which blocks the passage of the RF signals appearing on the surge protected AC line and neutral, while permitting the 60 Hertz AC power to pass to the surge protected AC outlets.  
         [0022]      FIG. 4  is a functional block diagram of the base or extension unit of an embodiment of the present invention. It comprises power supply  100  which provides the regulated DC voltages required by the integrated circuits which perform the signal processing. The base or extension unit has a high pass filter  102  which is connected to the AC power line and couples the broadband RF signals on the AC power line to processor  106  while, at the same time, blocking the 60 Hertz AC signals. A 25 MHz oscillator  104  is connected to processor  106  and functions as the system clock. Also connected to processor  106  are electrically erasable programmable read only memory devices (EEPROMs)  108 . Connected between processor  106  and RJ45 jack  112  is ethernet physical layer interface  110 . The RJ45 jack is connected to a device such as a cable modem or the network interface card of a computer which transmits and receives broadband digital signals.  
         [0023]     In the preferred embodiment of the invention, EEPROMs  108  are three-wire serial devices made by Atmel Corporation, 2325 Orchard Parkway, San Jose, Calif. 95131. In particular, preferred EEPROMs are Atmel AT93C46 devices. The Atmel website is www.atmel.com. In the preferred embodiment, the ethernet physical layer interface is made by Micrel Semiconductor, 2180 Fortune Drive, San Jose, Calif. 95131. In particular, the preferred Micrel ethernet physical layer interface is Micrel KS8721SL. The Micrel website is www.micrel.com. In the preferred embodiment, the preferred processor is made by Intellon Corporation, 5100 West Silver Springs Blvd., Ocala, Fla. 34482. In particular, the preferred processor is the Intellon INT5200 Single Chip PowerPacket™ Transceiver. The Intellon website is www.intellon.com.  
         [0024]     Each local module  10  and each remote module  12  has a unique “MAC” number assigned to it. The same is true of each cable modem and each computer network interface card. MAC is sometimes (incorrectly) referred to as Media Access Control but the correct term is Medium Access Control. See Newton&#39;s Telecom Dictionary, 16 Edition, for a full explanation of MAC. Digital signals arriving at RJ45  112  are in packet form and contain the MAC address of the local or remote module. Ethernet physical layer interface  110  supports an MII (Media Independent Interface) which facilitates communication with processor  106 . As explained in Newton&#39;s Telecom Dictionary, the MII is part of the Fast Ethernet specification and is used to connect the MAC layer to the physical layer. The processor in base unit  20  changes the MAC address in the incoming digital signals to that of extension unit  30  and converts the incoming digital signals to RF signals which are then placed on the AC power line. If extension unit  30  is connected to the network interface card in a computer and the computer user desires to send an e-mail over the internet, the extension unit receives the packets of digital information from the computer containing the MAC number of the extension unit, the extension unit changes the MAC number to that of the base unit and converts the digital signals from the computer to RF signals which are then placed on the AC power line which, as noted earlier, forms a local area network (LAN).  
         [0025]     Accordingly, although the above description of illustrative embodiments of the present invention, as well as various illustrative modifications and features thereof, provides many specificities, these enabling details should not be construed as limiting the scope of the invention, and it will be readily understood by those persons skilled in the art that the present invention is susceptible to many modifications, adaptations, variations, and equivalent implementations without departing from this scope and without diminishing its attendant advantages. It is further noted that the terms and expressions have been used as terms of description and not terms of limitation. There is no intention to use the terms or expressions to exclude any equivalents of features shown and described or portions thereof. It is therefore intended that the present invention is not limited to the disclosed embodiments but should be defined in accordance with the claims that follow.