Method and apparatus for detecting a compatible phantom powered device using common mode signaling

• US 6,804,351 B1
• Filed: 11/09/2000
• Issued: 10/12/2004
• Est. Priority Date: 11/09/2000
• Status: Expired due to Fees

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Karam, Roger A.
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Pham, Tuan
• Application Number:
  US09/710,388
• Time in Patent Office: 1,433 Days
• Field of Search: 379/93.09, 379/93.36, 379/413.02, 379/102.04, 379/106.04, 370/110, 370/79, 370/180, 370/185, 370/351, 713/310, 307/17, 307/412
• US Class Current: 379/413
• CPC Class Codes: H04M 19/001 Current supply source at the exchanger providing current to substations

Abstract

A method and an apparatus provide for determining whether a data terminal equipment (DTE) device represents a compatible device lacking an independent power supply and adapted to be powered using phantom power over a wired connection from a communications device such as a switch. A detection signal may be transmitted from the communications device to an identity network connected to the DTE. A response detection signal may be returned and checked in a receiver at the communications device. A switch may then be closed to provide phantom power if the result of the check indicates that the DTE is a compatible device adapted to receive phantom power. Compatible DTE device may include telephones, Voice over IP (VoIP, IP or Ethernet) telephones, network access devices, computers, and the like.

Claims

1. A data terminal equipment (DTE) device comprising:

a port having a plurality of electrical conductors for communicating with a communications device;

a first transformer winding coupled to a first pair of said plurality of electrical conductors and a first center tap disposed in said first transformer winding;

a second transformer winding coupled to a second pair of said plurality of electrical conductors and a second center tap disposed in said second transformer winding;

a power processor having a first and second input for receiving phantom power and a first and second output for providing electrical power to the DTE device;

a switch controlled by a signal on said first pair of said electrical conductors, said switch having a switch input coupled to said first center tap and a switch output coupled to said first input of said power processor, said second input of said power processor coupled to said second center tap; and

an identity network coupled between said first center tap and said second center tap.

2. An apparatus in accordance with claim 1 wherein said identity network comprises a capacitor.

3. An apparatus in accordance with claim 1 wherein said identity network comprises a resistor.

4. An apparatus in accordance with claim 1 wherein said identity network comprises an inductor.

5. An apparatus in accordance with claim 1 wherein said identity network comprises a diode.

6. An apparatus in accordance with claim 5, wherein said identity network comprises a zener diode.

7. An apparatus in accordance with claim 1 wherein said identity network comprises a serial memory device having data stored therein.

8. An apparatus in accordance with claim 1, wherein said switch includes a control input and said control input is coupled to said switch input.

9. An apparatus in accordance with claim 1 wherein said port includes an RJ-45 type connector.

10. A method for providing a compatible communications device with a signal indicating that phantom power should be supplied to a connected data terminal equipment (DTE) device, said method comprising:

receiving a detection signal over a first pair of conductors;

coupling said first pair of conductors across a first transformer winding, said first transformer winding including a first center tap;

extracting a signal at said first center tap;

coupling an identity network between said first center tap and a second center tap of a second transformer winding;

generating a response signal by applying said extracted signal to an input of said identity network; and

transmitting said response signal over a second pair of conductors by applying an output of said identity network to said second center tap and coupling said second pair of conductors across said second transformer winding, said second center tap being a center tap of said second transformer winding.

11. A method in accordance with claim 10, further comprising:

receiving phantom power between said first center tap and said second center tap.

12. A method in accordance with claim 11, further comprising:

applying said phantom power to a power processor.

13. A method in accordance with claim 12, wherein:

the phantom power is applied to the power processor through a switch responsive to the presence of phantom power between said first and second center taps.

14. An apparatus for providing a compatible communications device with a signal indicating that phantom power should be supplied to a connected data terminal equipment (DTE) device, said apparatus comprising:

means for receiving a detection signal over a first pair of conductors;

means for coupling said first pair of conductors across a first transformer winding, said first transformer winding including a first center tap;

means for extracting a signal at said first center tap;

means for coupling an identity network between said first center tap and a second center tap of a second transformer winding;

means for generating a response signal by applying said extracted signal to an input of said identity network; and

means for transmitting said response signal over a second pair of conductors by applying an output of said identity network to said second center tap and coupling said second pair of conductors across said second transformer winding, said second center tap being a center tap of said second transformer winding first winding of said second transformer.

15. An apparatus in accordance with claim 14, further comprising:

means for receiving phantom power between said first center tap and said second center tap.

16. An apparatus in accordance with claim 15, further comprising:

means for applying said phantom power to a power processor.

17. An apparatus in accordance with claim 16, wherein:

the phantom power is applied to the power processor through a switch responsive to the presence of phantom power between said first and second center taps.