Cable resistance determination in high-power PoE networks
An exemplary implementation of the present disclosure is a power sourcing equipment (PSE) for determining a resistance of a powered cable. The PSE includes a first supply voltage to cause a first current to flow through first and second output terminals of the PSE. The PSE also includes a second supply voltage to cause a second current to flow through third and fourth output terminals of the PSE. The PSE further includes a current modulation circuit offsetting the second current from the first current to create an offset voltage between the second and the first supply voltages to determine the resistance of the powered cable. The current modulation circuit can offset the second current from the first current utilizing a variable resistance switch to adjust the second current.
1. A power sourcing equipment (PSE) for determining a resistance of a powered cable, said PSE comprising:
a first supply voltage to cause a first current to flow through first and second output terminals of said PSE;
a second supply voltage to cause a second current to flow through third and fourth output terminals of said PSE;
a current modulation circuit offsetting said second current from said first current to create an offset voltage between said second and said first supply voltages to determine said resistance of said powered cable.
2. The PSE of claim 1 wherein said current modulation circuit offsets said second current from said first current utilizing a variable resistance switch to adjust said second current.
3. The PSE of claim 2 wherein said variable resistance switch comprises at least one transistor whose Rdson is adjusted.
4. The PSE of claim 1 wherein said current modulation circuit forces said offset voltage to remain below a pre-determined maximum value.
5. The PSE of claim 1 wherein said PSE applies said first and second supply voltages to a powered device over said powered cable.
6. The PSE of claim 1 wherein said PSE is utilized in a Power over Ethernet (PoE) network.
7. A method for determining a resistance of a powered cable utilized by a power sourcing equipment (PSE) in a Power over Ethernet (PoE) network, the method comprising:
applying a first supply voltage to cause a first current to flow through first and second output terminals of said PSE;
applying a second supply voltage to cause a second current to flow through third and fourth output terminals of said PSE;
offsetting said second current from said first current to create an offset voltage between said second and said first supply voltages to determine said resistance of said powered cable.
8. The method of claim 7 wherein said offsetting said second current from said first current utilizes a variable resistance switch to adjust said second current.
9. The method of claim 8 wherein said variable resistance switch comprises at least one transistor whose Rdson is adjusted.
10. The method of claim 7 comprising forcing said offset voltage to remain below a pre-determined maximum value.
11. The method of claim 7 wherein said first and second supply voltages are applied to a powered device over said powered cable.
12. The method of claim 7 wherein a current modulation circuit determines said resistance of said powered cable using said offset voltage.
13. The method of claim 7 wherein a current modulation circuit determines said resistance of said powered cable using said first current and said second current.
14. A system for determining a resistance of a powered cable, the system comprising:
a powered device;
a PSE applying a first supply voltage to said powered device over said powered cable and causing a first current to flow through first and second conductive pairs in said powered cable;
said PSE applying a second supply voltage to said powered device over said powered cable and causing a second current to flow through third and fourth conductive pairs in said powered cable;
a current modulation circuit offsetting said second current from said first current to create an offset voltage between said second and said first supply voltages to determine said resistance of said powered cable.
15. The system of claim 14 wherein said current modulation circuit offsets said second current from said first current utilizing a variable resistance switch to adjust said second current.
16. The system of claim 14 wherein said variable resistance switch comprises at least one transistor whose Rdson is adjusted.
17. The system of claim 14 wherein said current modulation circuit forces said offset voltage to remain below a pre-determined maximum value.
18. The system of claim 14 wherein said current modulation circuit is within said PSE.
19. The system of claim 14 wherein said current modulation circuit determines said resistance of said powered cable using said offset voltage.
20. The system of claim 14 wherein said powered cable is a powered Ethernet cable.