Detecting legacy powered device in power over ethernet system

• US 20060168458A1
• Filed: 10/19/2005
• Published: 07/27/2006
• Est. Priority Date: 01/25/2005
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Corporation (Analog Devices, Inc.)
• Inventors: Stineman, John Arthur Jr., Heath, Jeffrey Lynn
• Granted Patent: US 7,856,561 B2
• Time in Patent Office: Days
• US Class Current: 713/300
• CPC Class Codes: H04L 12/10 Current supply arrangements

Abstract

Novel system and methodology for detecting a Powered Device (PD) in a Power over Ethernet (PoE) system. A PD probing circuit generates a detection signal supplied to the PD and determines a PD response signal produced in response to the detection signal. Based on the PD response signal, the control circuit determines a detection value for identifying the PD. In particular, the control circuit concludes that the PD is a device satisfying a PoE standard if the detection value is in a first predetermined range, and concludes that the PD is a legacy PD device if the detection value is in a second predetermined range outside of the first predetermined range.

Claims

1. A system for providing power to a powered device (PD) in a Power over Ethernet (PoE) system, comprising:

a PD probing circuit for determining a PD response signal produced in response to a detection signal supplied to the PD, and

a control circuit responsive to a detection value determined based on the PD response signal, the control circuit being configured for determining that the PD is a device satisfying a PoE standard if the detection value is in a first predetermined range, and determining that the PD is a legacy PD device if the detection value is in a second predetermined range outside of the first predetermined range.

2. The system of claim 1, wherein the control circuit is configured to determine whether or not the PD is the legacy device by comparing the detection value with a predetermined threshold detection value.

3. The system of claim 1, wherein the detection value includes a detection resistance value and the control circuit is configured to determine that the PD is the legacy PD device if the detection resistance value is less than a predetermined threshold resistance value.

4. The system of claim 1, wherein the detection value includes a detection resistance value and the control circuit is configured to determine that the PD is the legacy PD device if the detection resistance value is of a negative value.

5. The system of claim 1, wherein the PD probing circuit is configured for producing a first detection current followed by a second detection current smaller than the first detection current.

6. The system of claim 5, wherein the control circuit is configured to detect the legacy PD device if a first response voltage produced in response to the first current is smaller than a second response voltage produced in response to the second current.

7. The system of claim 5, wherein the control circuit is configured to detect the legacy PD device if a first response voltage produced in response to the first current is larger than a second response voltage produced in response to the second current, and a difference between the first response voltage and the second response voltage is less than a predetermined threshold value.

8. The system of claim 5, wherein the control circuit is configured to detect the legacy device when a detection resistance value defined by a difference between a first response voltage produced in response to the first current and a second response voltage produced in response to the second current, is less than a predetermined threshold resistance value.

9. The system of claim 8, wherein the predetermined threshold resistance value is less than a minimum signature resistance value defined by the PoE standard.

10. A method of providing power to a powered device (PD) in a Power over Ethernet (PoE) system, comprising the steps of:

producing a detection signal supplied to the PD to determine a PD response signal, and

based on the PD response signal, determining that the PD is a device satisfying a PoE standard if the detection value is in a first predetermined range, and determining that the PD is a legacy PD device if the detection value is in a second predetermined range outside of the first range.

11. The method of claim 10, wherein the step of producing a detection signal includes producing a first detection signal followed by a second detection signal having a smaller value than the first detection signal.

12. The method of claim 11, wherein the legacy device is detected when a detection resistance value defined by a difference between a first response signal produced in response to the first detection signal and a second response signal produced in response to the second detection signal, is less than a predetermined value.

13. The method of claim 12, wherein the predetermined value is less than a minimum signature resistance value defined by the PoE standard.

14. The method of claim 11, wherein the legacy device is detected when a detection resistance value defined by a difference between a first response signal produced in response to the first detection signal, and a second response signal produced in response to the second detection signal, is a negative value.

15. The method of claim 11, wherein the legacy PD device is detected if a first response signal produced in response to the first detection signal is smaller than a second response signal produced in response to the second detection signal.

16. The method of claim 11, wherein the legacy PD device is detected if a first response signal produced in response to the first detection signal is larger than a second response signal produced in response to the second detection signal, and a difference between the first response signal and the second response signal is less than a pre-set threshold value.

17. A Power Sourcing Equipment (PSE) in a Power over Ethernet (PoE) system, comprising:

a powered device (PD) detection source for producing first detection current supplied to the PD to determine first response voltage, and for producing second detection current smaller than the first detection current to determine second response voltage, and

a detecting circuit for determining that the PD is a legacy PD if a detection resistance value defined by a result of subtracting a value of the second response voltage from a value of the first response voltage is less than a predetermined value smaller than a minimum signature resistance value defined by IEEE 802.3af standard.

18. The PSE of claim 17, wherein the legacy PD is detected if the detection resistance value is a negative value.

19. The PSE of claim 17, wherein the detecting circuit is further configured to detect a PD that satisfies requirements of the IEEE 802.3af standard if the detection resistance value is within a required signature resistance range.