Abstract:
A system and method provide dynamic termination of the unused wired connections in a communications interface of a communications device. An interconnected controller, switch, and termination circuit are provided to connect at least one unused wired connection of the communications interface to ground in response to a pre-determined event. Dynamic termination of one or more unused wired connections of the communications interface can occur while still allowing power delivery, via the interface, to the communications device to maintain operation of the communications device.

Description:
TECHNICAL FIELD 
     The present invention relates generally to communication services. It particularly relates to a method and system for providing dynamic termination capability for an unused wired connection in a communications interface. 
     BACKGROUND OF THE INVENTION 
     Communications systems (e.g., public switched telephone system, cable television, LANs—local area networks, etc.) have been rampantly deployed in the marketplace for a number of years to provide high-speed, broadband communications services. A significant factor in providing quality communications services is the reduction and/or elimination of interference (e.g., electromagnetic interference—EMI, spurious radiation/emissions, noise) in the communications medium that attenuates the received signal-to-noise ratio at the receiving end. To ensure this goal, a plurality of different communications media have been developed to help reduce the unwanted interference (e.g., coax, shielded twisted pair, optical fiber). 
     However, new communications services that allow power along with data to be delivered, via the communications medium, to a receiving communications device require even more stringent interference reduction measures to be taken. One exemplary power/data communications standard is the Power over LAN standard in accordance with the IEEE 802.3af Draft 3.0 February 2002 specification hereby incorporated by reference. This standard has been recently developed for LANs (e.g., Ethernet) allowing the service provider to deliver power and data over the communications medium (e.g., category 5—CAT 5 cable) to the receiving communications device via an input port (e.g., 8-pin RJ-45 port). 
     Although the standard does specify techniques to isolate the LAN power feed from the rest of the circuitry in the receiving communications device (DTE—data terminal equipment or PD—powered device), there is no mention of reducing and/or eliminating the spurious emissions potentially caused by the unused pins within the input port since only four of the eight pins may be used for power delivery and data communications (e.g., pins  1 - 3 ,  6 ). During power delivery from and data communications service with the provider, coupling (from spurious emissions) may occur from the LAN cable on to the unused pins in the input port and cause disruptions in the operation of the communications device (e.g., computing device, telephone, camera, wireless communications device, etc.). However, due to the detection phase of the standard, permanent termination of these unused pins is not a viable solution since the communications device must provide a pre-determined input impedance (e.g., signature) to the power supply equipment (PSE) of the LAN service provider to properly identify the communications device as standard-compliant before delivering power to the device. Therefore, permanent termination of the unused pins would alter the value of this pre-determined impedance and thus prevent injection of the necessary power to commence device operation. 
     Therefore, due to the problems arising from spurious emissions radiating from unused pins in a communications interface of a communications device that may not be solved by permanent termination, there is a need to provide dynamic termination of these unused pins while still allowing (regular) power delivery, via the interface, to the communications device to maintain (normal) operation of the communications device. 
     SUMMARY OF THE INVENTION 
     The system and method of the present invention overcomes the previously mentioned problems by providing dynamic termination of unused wired connections in a communications interface of a communications device. An interconnected controller, switch, and termination circuit are provided to connect at least one unused wired connection of the communications interface to ground in response to a pre-determined event. Advantageously, embodiments of the present invention described herein may be used to dynamically terminate one or more unused wired connections of the communications interface while still allowing (regular) power delivery, via the interface, to the communications device to maintain (commence) operation of the communications device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an exemplary input section to a communications device allowing power delivery found in the background art. 
         FIG. 2  is a table showing the pin designations for an exemplary communications interface allowing power delivery found in the background art. 
         FIG. 3  is a block diagram showing the parameter requirements for an exemplary input section to a communications device allowing delivery found in the background art. 
         FIG. 4  is a block diagram of an exemplary isolation switch found in the background art. 
         FIG. 5  is a block diagram of an exemplary input section to a communications device providing dynamic termination in accordance with an embodiment of the present invention. 
         FIG. 6  is a flow chart illustrating a method according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a block diagram of an input section  100  to a communications device (not shown) allowing power delivery (injection) in accordance with the background art. Input section  100  includes input port  102 , electromagnetic (EMI) filters  104 ,  110 , resistor  106 , isolation switch  108 , transceiver physical device (PHY)  109 , and DC-DC power supply  112 . Input port  102  may include RJ-45 (registered jack-45) and transformer portions. Isolation switch  108  and resistor  106  assist in a detection mode, as described in greater detail later, for the circuitry of the input section  100 . DC-DC power supply  112  acts as the power supply for the communications device and should reflect the power requirements of IEEE 802.3af specification which include, but are not limited to, less than 12.95 Watt power consumption, input-to-output isolation of 1500 Vrms, and other parameters. 
     The input port  102  may function as a communications interface providing a standard data/power connection for local area network (e.g., Ethernet) devices allowing a LAN service provider to communicate data and deliver power, preferably via category-5 (CAT-5) cabling, with the communications device that is LAN-compatible. PHY  109  acts as a transceiver for data communications to and from input port  102  via data lines  101  and receives power from supply  112 . Although not shown, other transceiver PHYs may be used as transceivers for other communications interfaces (e.g., PCMCIA—Personal Computer Memory Card Industry Association interface) on the communications device and receive power from interconnected power supply  112 . 
     As shown in  FIG. 2 , the input port  102  includes eight wired pins (connections) for communicating with the LAN cable link and communicating information to and from the communications device in accordance with the IEEE 802.3af specification. These eight pins may include data pins  1 - 3 , and  6  that may be used to transfer data and deliver power to the communications device leaving the other pins unused (e.g., pins  4 - 5 ,  7 - 8 ). Additionally, input port  102  may include receiving/transmitting transformers to help transport/convert power received from the LAN service provider to the power supply  112  of the communications device. Preferably, these transformers are in accordance with the IEEE 802.3af specification and are able to handle 450 mA and 350 mA as peak and average current values, respectively. Advantageously, a connected communications device may include, but is not limited, to any LAN-compatible device including telephones, computing devices, cameras, wireless communications devices, and other LAN-compatible devices. 
     EMI filter  104  may protect the circuitry of the input section  100  from external surges and spikes produced from ESD (electrostatic discharge) or other testing, and also filter emissions generated by the input section circuitry. EMI filter  110  may isolate the link side (with RJ-45 interface) of the circuit from the DC-DC power supply  112  when isolation switch  108  initiates the detection (signature mode) for the circuitry. 
     In accordance with IEEE 802.3af, prior to power delivery, the LAN service provider may initiate a signature (detection) mode to discern whether its power supply equipment is connected to an open link, a compatible power-over-LAN device, or an incompatible power-over-LAN device. If the service provider identifies anything other than a compatible power-over-LAN device, then no power injection will occur. As shown in  FIG. 3 , acceptable circuit parameters of the input section  100  for proper signature detection are shown in accordance with 802.3af specification. 
     As shown in  FIG. 1 , the key detection mode elements are the resistor  106  (a 25 KΩ resistor) and the isolation switch  108 . During detection (signature) mode, a low voltage (e.g., much less than 30 volts) is transmitted into input section  100  and a pre-determined input impedance, created by the 25 KΩ resistor  106 , is detected by the service provider. Upon detection of this impedance signature, voltage upon the input line increases to at least 30V, the turn-on voltage for the communications device. When switch  108  detects a voltage of at least 30V and less than 36V (e.g., the turn-off voltage for the communications device), the switch  108  activates to connect the link (cable) side with the DC-DC power supply  112  to produce the necessary power for device operation that is output on line  114  for delivery to various portions (e.g., processor, display, hard-drive, CD-ROM drive, etc.) of the device. As shown in  FIG. 4 , isolation switch  108  may be a mosfet circuit  400  biased to “turn-on” at 30 volts to complete the link connection to the DC-DC power supply  112 . 
       FIG. 5  is a block diagram of an exemplary input section  200  to a communications device providing dynamic termination in accordance with an embodiment of the present invention. Elements of input section  200  common to input section  100  have been included in  FIG. 5 . New elements of input section  200  include interconnected switch controller  124 , switch  122 , and termination circuit  120 . Advantageously, switch controller  124  may receive power from power supply  112  and switch  122  may be embodied as a relay circuit to withstand 1500 V rms . Although shown as separate elements, it is noted that termination circuit  120  and switch  122  may be co-located and their configuration in  FIG. 5  is solely exemplary and should not be viewed as a limitation upon the present invention. 
     Advantageously, switch  122  connects to ground and termination circuit  120  connects to the unused pins of communications interface (RJ-45)  102  (e.g., pins  4 - 5 ,  7 - 8 ). Termination circuit  120  may be embodied as an RC circuit (impedance of R+1/jωC). During the signature mode (before power injection) of operation, switch  122  is open (inactive) making the combination of switch  122  and termination circuit  120  an effective open circuit ((1/jωC)=0) which does not change the expected impedance value (e.g., R=25 KΩ) seen by the LAN service provider during this mode in accordance with the IEEE 802.3af specification. 
     Once the communications device is properly identified as a LAN-compatible device, the power supply equipment of the service provider may send an input voltage increasing over 30 volts to input port  102 . Isolation switch  108  senses the turn-on voltage of 30-36 volts being satisfied, and completes the circuit connection between input port  102  and power supply  112 . 
     Upon closing of the switch  108 , switch controller  124  receives a control signal  125 , generated by the isolation switch  108 , and receives a digital control signal  127  from PHY  109 . Control signal  125  may be a digital signal generated using an analog-to-digital (A/D) converter (not shown) to convert an analog trigger (indicating a closed switch  108 ) from the MOSFET circuit  400  to a digital control signal  125  (high signal with value of “1”) for switch controller  124 . Digital control signal  127  (Link OK) may be a digital signal, generated by PHY  109  in accordance with IEEE 802.3af specification, that goes “high” (digital value of “1”) when the turn-on voltage is reached to commence (normal) operation of the communications device. At switch controller  124 , the combination of receiving two “high” input control signals  125 ,  127  may trigger (e.g., via a logic function—“AND” of the two control inputs) switch controller  124  to send a control signal  129  to switch  122  instructing the switch  122  to close (become active) and complete the connection between unused pins ( 4 - 5 ,  7 - 8 ), via termination circuit  120 , and ground. 
     Advantageously, this process may be repeated upon any subsequent power-up of the communications device as both switches  108 ,  122  effectively open (become inactive) upon power-down of the communications device as the voltage goes below the turn-on voltage of 30 volts to reverse the process and separate the communications link (cable) portion from the power supply  112 . Also, switch controller  124  receives a digital low signal (e.g. “0”) from both isolation switch  108  and PHY  109  indicating that power-down has occurred which triggers, via the control signal  129  sent to switch  122 , removal of the termination to ground for unused pins of the input port  102 . Advantageously, grounding the unused pins reduces and/or eliminates spurious emissions that may be produced from coupling of power, EMI, and other noise on to these unused pins from the LAN connection to input port  102 . It is noted that unused pins  4 - 5 ,  7 - 8  are solely exemplary and should not be viewed as any limitation upon the present invention. 
     Although particular structural configurations have been illustrated regarding the component parts of the input section  200  (e.g., the isolation switch  108  in  FIG. 4 ), it should be appreciated that such configurations are merely exemplary. The present invention can employ various component parts having various structural configurations without departing from the scope of the invention as claimed. 
     Advantageously, in accordance with embodiments of the present invention, the method and system disclosed herein enables the dynamic termination of at least one unused wired connection of a LAN interface port upon sensing of a turn-on voltage to commence power-over-LAN operation of the interconnected communications device. 
     Although the invention is primarily described herein using particular embodiments, it will be appreciated by those skilled in the art that modifications and changes may be made without departing from the spirit and scope of the present invention. As such, the method disclosed herein is not limited to what has been particularly shown and described herein, but rather the scope of the present invention is defined only by the appended claims.