Abstract:
An apparatus for splitting differential signals and methods of operating the same result in a low cost passive multiport differential signal switcher. The multiport differential signal switcher for operating on a signal originating from a signal source comprises a first port having a first transmit port and a first receive port configured to receive a signal at the first transmit port coupled to a first switching element and a second switching element, a second port having a second transmit port and a second receive port configured to receive a signal at the second receive port coupled to the second switching element and a third switching element and a third port having a third transmit port and a third receive port configured to receive a signal at the third receive port coupled to the first switching element and a fourth switching element wherein the originating signal from the first transmit port turns-on the first switching element and the second switching element to pass the originating signal to the second receive port and the third receive port, respectively.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to networking of electronic devices and more particularly to a passive switching hub for networking multiple devices to a transmission medium. 
     2. Description of the Related Arts 
     A local area network is a communication system that allows personal computers, workstations, servers, and other network devices within a small area, such as a single building or a group of adjacent buildings, to transfer information between each other. Each device connected to the network communicates with other device on the network by following a standard which defines the operation of the network. One of the most widely accepted standards for local area networks is the IEEE 802.3 CSMA/CD Ethernet Protocol. 
     In the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) Ethernet Protocol, before transmitting data onto the network, each device first monitors the network to insure that no transmissions are currently in progress (Carrier Sense). When the network is idle (no transmissions in progress), each device can transmit information onto the network (Multiple Access). When more than one device transmits at the same time, each transmitting device must be able to detect this condition (Collision Detection), stop its transmission and retry. 
     The IEEE 802.3 CSMA/CD Ethernet protocol defines for physical layer specifications which differ primarily in the physical cables utilized. Coaxial cables are defined by a Thick Coax Ethernet (10BASE5), which utilizes a double-shielded coaxial cable, and a Thin Coax Ethernet (10BASE2), which utilizes a single-shielded coaxial cable. Twisted pair cables are 26 to 22 AWG unshielded wire. Two kinds of twisted pair exist. UTP is for unshielded, twisted pair, while STP is for shielded, twisted pair. UTP is what phone companies typically installed (though this is often not of high enough quality to support high-speed network use such as 10BaseT ethernet. UTP is graded according to its data carrying ability (e.g., Level 3, Level 4, Level 5). 10BaseT Ethernet requires at least Level 3 cable. Often what is now readily available is the Level 5 UTP having a RJ-45 connector. 
     Today, local area networks are becoming more and more prevalent and are often encountered to some degree by even casual computer users. Not only do personal computers, workstations, and servers utilize local area networks such as ethernet, but peripheral devices like printers, scanners, and digital cameras are also incorporating an ethernet interface. Ethernet being a relatively speedy and the widely accepted interface is becoming more popular in more devices. Thus, there is a growing need for providing readily available ethernet ports for new and existing devices, particularly for the causal computer users. 
     Even though multiple port hubs for ethernet having four ports, eight ports, 12 ports and even 24 ports are available, these hubs are often costly especially to cost conscience causal computer users. Moreover, even the smallest, a four port hub, takes up desk space and requires a separate power lead to an AC source. More often than not what is needed is an additional ethernet port than what is available. 
     For example, modern day network equipped computers have one network port and often that one network port is coupled to another network port fixed in of the wall for access to a local area network. Configured in this way leaves zero ports available for additional devices. The current available solutions for interfacing to another network equipped device are to 1) disconnect the current computer from the network and connect the other network device which may require crawling on hand and knees or 2) acquire a multiple port hub like the four port hub. 
     Even a stand alone user with only one network port on the back of the computer have needs for additional ports. If there is a printer connected to the network port and the user wants to connect a digital camera or scanner to the computer, the user will be unable without disconnecting and reconnecting already networked devices or purchasing at minimum a four port hub. 
     Therefore, it is desirable to provide a passive ethernet hub apparatus and methods of operating the same which provides a simpler less costly and cumbersome solution that better suits the network needs of its users. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for a multiport differential signal switcher and methods for operating the same which splits a transmission signal to provide multiple transmission signals. The multiport differential signal switcher is based on a plurality of switches for splitting the transmission signal. Thus, according to one aspect of the invention, the multiport differential signal switcher for operating on a signal originating from a signal source comprises a first port having a first transmit port and a first receive port configured to receive a signal at the first transmit port coupled to a first switching element and a second switching element, a second port having a second transmit port and a second receive port configured to receive a signal at the second receive port coupled to the second switching element and a third switching element, and a third port having a third transmit port and a third receive port configured to receive a signal at the third receive port coupled to the first switching element and a fourth switching element wherein the originating signal from the first transmit port turns-on the first switching element and the second switching element to pass the originating signal to the second receive port and the third receive port, respectively. 
     According to another aspect of the invention, the first switching element, the second switching element, the third switching element, and the fourth switching element each include a current switch. The first switching element includes a first resistor and a first npn transistor, a first end of the first resistor coupled to the first transmit port and a collector of the first npn transistor, a second end of the resistor coupled to a base of the first npn transistor, and an emitter of the first npn transistor coupled to the third receive port and an output of the fourth switching element, and the second switching element includes a second resistor and a second npn transistor, a first end of the second resistor coupled to the first transmit port and a collector of the second npn transistor, a second end of the second resistor coupled to a base of the second npn transistor, and an emitter of the second npn transistor coupled to the second receive port and an output of the third switching element. The first npn transistor of the first switching element and the second npn transistor of the second switching element are in an on-state. 
     According to another aspect of the invention, the third switching element includes a third resistor and a third npn transistor, a first end of the first resistor coupled to the second receive port and a collector of the third npn transistor, a second end of the resistor coupled to a base of the third npn transistor, and an emitter of the third npn transistor coupled to a third transmit port and an input of a fifth switching element, and the fourth switching element includes a fourth resistor and a fourth npn transistor, a first end of the fourth resistor coupled to the third receive port and a collector of the fourth npn transistor, a second end of the fourth resistor coupled to a base of the fourth npn transistor, and an emitter of the fourth npn transistor coupled to a second transmit port and an input of a sixth switching element. The third npn transistor of the third switching element and the fourth npn transistor of the fourth switching element are in an off-state. The first switching element, the second switching element, the third switching element, and the fourth switching element each include an unidirectional current switch. 
     An apparatus and method of operating a multiport differential signal switcher are provided whereby no external power supply is needed to supply power to the multiple differential signal switcher to split a signal to produce two signals. Other aspects and advantages of the present invention can be seen upon review of the figures, the detailed description, and the claims which follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 illustrates an embodiment of a passive ethernet hub according to the present invention. 
     FIG. 2 illustrates an alternative embodiment of a passive ethernet hub according to the present invention. 
     FIG.  3 A and FIG. 3B illustrate simplified switching schematics of the passive Ethernet hub in accordance to the present invention. 
     FIG. 4 illustrates a detailed schematic of the passive ethernet hub in accordance to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will be described with respect to the Figures in which FIG. 1 generally shows an embodiment of a passive ethernet hub  10  for splitting an ethernet signal. The passive ethernet hub  10  includes an I/O port  2 , I/O port  4  and I/O port  6  that expands a single ethernet port to two ethernet ports. The I/O ports are designated as port A, port B and port C. The port designations will be used throughout this disclosure for the passive ethernet hub. The I/O port  2  mates to a standard RJ-45 receptacle commonly used for ethernet CSMA/CD based networks. These standard RJ-45 receptacles are often found on the back of network ready computers, network outlets in networked office environments, and ethernet hubs in a networked environment. The RJ-45 is serial connector which looks very much like a standard telephone connector, except it houses eight wires instead of four. I/O port  4  and I/O port  6  provide receptacles for receiving RJ-45 cabling. Gender changers and adapters are readily available to enable users of the passive ethernet hub  10  different connect configurations to suit their particular applications. Accordingly, FIG. 2 illustrates another embodiment of a passive ethernet hub  20 . The passive ethernet hub  20  is aesthetically symmetric and configured with three RJ-45 receptacles of which receptacle  22  is shown in FIG.  2 . Each receptacle electrically mates to RJ-45 cabling. Thus, a single ethernet port is expanded to include two ethernet ports. The passive ethernet hub  10  and the other embodiment of the passive ethernet hub  20  function like a phone outlet splitter or cable splitter that are commonly found in modern households but also provides standard hub functions well known for ethernet. 
     FIG.  3 A and FIG. 3B illustrate simplified block diagrams of the passive ethernet hub  20 . A hexagon schematic  32  and a hexagon schematic  34  depict a series of switches for coupling the various signals between the I/O ports of the passive ethernet hub  20 . The hexagon schematic  32  of FIG. 3A shows positive signal switches for the passive ethernet hub  20 . The hexagon schematic  34  of FIG. 3B shows negative signal switches for the passive ethernet hub  20 . An ethernet signal is a differential signal that uses two wires, one of which carries the normal signal (V) and the other carries an inverted version signal (−V). A differential amplifier at the receiver (not shown) subtracts the inverted signal from the normal signal to yield a signal proportional to V. This subtraction is intended to cancel out any noise induced in the wires, on the assumption that the same level of noise will have been induced in both wires. Often times, twisted pair wiring is used to try to ensure that the noise is induced in both wires. The hexagon schematic  32  depicts the positive signal (V) and the hexagon schematic  34  depicts the inverted version of the positive signal (−V). Since the inverted version of the positive signal behave similarly as the positive signal, for clarity and brevity sakes, the positive signals for the passive ethernet hub are described in more detail. 
     The three ports of the passive ethernet hub designated as port A, port B, and port C each include S+, S−, R+, and R− representing a send positive signal, send negative signal, receive positive signal, and a receive negative signal, respectively. Thus, each of the three ports has four signals associated with the port. Port A has AS+, AS−, AR+, and AR−; port B has BS+, BS−, BR+, and BR−; and port C has CS+, CS−, CR+, and CR−. 
     The hexagon schematic  32  includes signal nodes for AS+, AR+, BS+, BR+, CS+, and CR+. Similarly, the hexagon schematic  34  includes signal nodes for AS−, AR−, BS−, BR−, CS−and CR−. Since ethernet signals are transmitted serially over a shared network channel that is attached to each ethernet equipped device, a device sending data to another device first listens to the shared network channel and determines the channel is free before transmission of the ethernet signals. A detailed discussion of an ethernet system is found in “Practical Networking with Ethernet” by Charles E. Spurgeon ISBN: 1-85032-885-4 and is hereby incorporated by reference. 
     Coupling the passive ethernet hub  20  to an ethernet network as published in the IEE 802.3 standard, the hub  20  receives an ethernet signal from a device coupled to port A AS+as shown in hexagon schematic  32 , switch AB closes and switch AC closes to pass the ethernet signal to port B BR+ and port C CR+. The adjacent switches BA and CB remain open and isolate nodes BS+ and CS+ from the applied ethernet signal at port A AS+. Similarly, when a ethernet signal applied to port B BS+, switch BA closes and switch BC closes to provide a path for the ethernet signal to port A AR+ and port C CR+. The adjacent switches CA and AC remain open and isolate nodes AS+ and CS+ from the applied ethernet signal at port B BS+. Ethernet signals applied to port C CS+ are routed to AR+ and BR+ via switch CA and switch CB. The adjacent switches AB and BA remain open and isolate nodes AS+ and BS+ from the applied ethernet signal at port C CS+. 
     The inverted signals for the passive ethernet hub  20  are shown in the hexagon schematic  34 . Ethernet signals received at port A line AS− activates switch AB− and switch AC− to provide a signal path for the ethernet signal to port B line BR− and port C CR−. Ethernet signals received at port B line BS− activates switch BA− and switch BC− to provide a signal path for the ethernet signal to port A line AR− and port C CR−. Similarly, ethernet signals received at port C line CS− activates switch CA− and switch CB− to provide a signal path for the ethernet signal to port A line AR− and port B BR−. Thus, the passive ethernet hub  20  divides a single ethernet signal applied to port A, for example, to provide the ethernet signal at both port B and port C. 
     FIG. 4 illustrates a schematic for an embodiment of the passive ethernet hub  20 . Switches AB, AC, BA, BC, CA, and CB for the positive signal are shown. Switches AB−, AC−, BA−, BC−, CA−, and CB− for the inverse of the positive signal are also shown. Each switch comprises a combination of resistors and transistors that have been optimized to function as current switches. The resistors shown are 220 ohms; the transistors are npn transistors 2N3904A. Capacitors are 0.01 micro-farads. The capacitors isolates DC components of an ethernet signal that may be present. In most cases, the capacitors are not needed for the passive ethernet hub  20  to function but are included for compatibility to transceivers that exhibit a DC component. Those skilled in the art will appreciate that variations or substitutions to the specified components can be used to achieve the same desired result. For example pnp transistors or mosfets may be substituted for the npn transistors to provide the switching functions. 
     In the present embodiment, port A, port B, and port C are RJ-45 receptacles with eight (8) pins. The RJ-45 receptacles are also referred to as the female connector. Following the convention for ethernet using the RJ-45 pinout, pin  1  is TX+, pin  2  TX−, pin  3  RX+, and pin  6  RX−. Referring to FIG. 3, port A pin  1  corresponds with AS+, and port A pin  3  corresponds with AR+. Port B pin  1  corresponds with BS+, and port B pin  3  corresponds with BR+. Port C pin  1  corresponds with CS+, and port C pin  3  corresponds with CR+. Similarly, Port A pin  2  corresponds with AS−, and port A pin  6  corresponds with AR−. Port B pin  2  corresponds with BS−, and port B pin  6  corresponds with BR−. Port C pin  2  corresponds with CS−, and port C pin  6  corresponds with CR−. Capacitor  405  is coupled between AS+ and node  406 . Switch AB includes resistors  421  and  423  and transistors  422  and  423 . Resistor  421  is coupled between node  406  and base of transistor  422 . Collector of transistor  422  is coupled to emitter of transistor  424 . Resistor  423  is coupled between node  408  and base of transistor  424 . Collector of transistor  424  is coupled to emitter of transistor  422  and node  408 . Capacitor  407  is coupled between node  408  and port B pin  3 , BR+. Switch AC include resistors  426  and  428  and transistors  427  and  429 . Resistor  428  is coupled between node  406  and base of transistor  429 . Collector of transistor  429  is coupled to emitter of transistor  427 . Resistor  426  is coupled between node  410  and base of transistor  427 . Collector of transistor  427  is coupled to emitter of transistor  429  and node  410 . Capacitor  409  is coupled between node  410  and port C pin  3 , CR+. 
     Switch CB includes resistors  446  and  448  and transistors  447  and  449 . Resistor  446  is coupled between node  408  and base of transistor  447 . Collector of transistor  447  is coupled to emitter of transistor  449 . Resistor  448  is coupled between node  412  and base of transistor  449 . Collector of transistor  449  is coupled to emitter of transistor  447  and node  412 . Capacitor  411  is coupled between node  411  and port C pin  1 , CS+. Switch BC includes resistors  436  and  438  and transistors  437  and  439 . Resistor  438  is coupled between node  410  and base of transistor  439 . Collector of transistor  439  is coupled to emitter of transistor  437 . Resistor  436  is coupled between node  414  and base of transistor  437 . Collector of transistor  437  is coupled to emitter of transistor  439  and node  414 . Capacitor  413  is coupled between node  413  and port B pin  1 , BS+. 
     In an operation example, as port A pin  1  receives an ethernet signal, switch AB and switch AC turns on to provide a path for the ethernet signal to port B pin  3  and port C pin  3 . In particular, the ethernet signal applied to port A pin  1 , AS+ activates transistor  422  of switch AB to provide a signal path to port B pin  3 , BR+; the ethernet signal also activates transistor  429  of switch AC to provide a signal path to port C pin  3 , CR+. However, transistor  447  and transistor  449  of switch CB and transistor  437  and transistor  439  of switch BC do not turn on. 
     An inverted ethernet signal also received at port A pin  2 , AS− activates switch AB− and switch AC−. In particular, transistor  462  of switch AB− turns on and transistor  467  of switch AC− turns on. The inverted ethernet signal travels via capacitor  455 , node  456 , transistor  462  of switch AB−, and capacitor  457  to port B pin  6 , BR− and via transistor  469  of switch AC−, and capacitor  460  to port C pin  6  CR−. Transistors  477  and  479  of switch BC− and transistors  487  and  488  of switch CB− remain in their off state and do not provide a signal path for the ethernet signal at node  461  and node  458 . Thus, a single ethernet signal received at port A is split to provide the ethernet signal at both port B and port C. 
     Ethernet signals applied at port B similarly routes the ethernet signal to port A and port C. Signals applied to port C routes to port A and port B. No external power supply cord or power transformer is needed to operate the signal splitting function. Thus, the passive ethernet hub provides a novel cost effective compact solution for networking ethernet equipped devices. 
     While the foregoing detailed description has described present embodiments of the apparatus and methods for a passive ethernet hub in accordance with this invention, it is to be understood that the above description is illustrative only and not limiting of the disclosed invention. Obviously, many modifications and variations will be apparent to the practitioners skilled in this art. Accordingly, the apparatus and methods for a passive ethernet hub have been provided. The passive ethernet hub splits an ethernet signal to provide multiple ethernet signals.