Common-mode filtering for converting differential signaling to single-ended signaling

1. An interface in a radiofrequency (RF) wireline communications system, the interface comprising:

a physical layer transceiver configured for coupling between a differential wireline channel medium and a functional device, the physical layer transceiver being an integrated circuit device having first and second differential wireline conductors configured for coupling to the differential wireline channel medium, and having first and second differential input/output conductors extending toward the functional device;

an impedance element configured to terminate a first one of the first and second differential input/output conductors to a ground of the communications system between the physical layer transceiver and the functional device, a second one of the first and second differential input/output conductors being configured for coupling to a single-ended cable that is configured for coupling to the functional device; and

a common-mode filter coupled, between the physical layer transceiver and the functional device, to both of the first and second differential input/output conductors.

2. The interface of claim 1 further comprising:

a printed circuit board, the physical layer transceiver integrated circuit device being mounted on the printed circuit board; and

first and second differential signal traces on the printed circuit board coupled to the differential input/output conductors; wherein:

the impedance element terminates a first one of the first and second differential signal traces to the ground of the communications system; and

the common-mode filter is coupled to both of the first and second differential signal traces.

3. The interface of claim 2 further comprising:

a single-ended cable connector mounted on the printed circuit board; wherein:

the second one of the first and second differential signal traces is coupled to the single-ended cable connector.

4. The interface of claim 3 wherein the single-ended cable comprises a shielded single-ended cable coupled to the single-ended cable connector.

5. The interface of claim 4 wherein the shielded single-ended cable comprises a coaxial cable.

6. The interface of claim 1 wherein:

the physical layer transceiver integrated circuit device comprises an integrated circuit die mounted on a substrate; and

the common-mode filter coupled to both of the first and second differential input/output terminals is mounted on the substrate.

7. The interface of claim 1 wherein:

the physical layer transceiver integrated circuit device comprises an integrated circuit die; and

the common-mode filter coupled to both of the first and second differential input/output conductors is formed on the integrated circuit die.

8. The interface of claim 1 wherein the common-mode filter comprises a common-mode choke configured to filter out common-mode signals on the first and second differential input/output conductors.

9. The interface of claim 1 wherein the common-mode filter comprises an active filter configured to filter out common-mode signals on the first and second differential input/output conductors.

10. The interface of claim 9 wherein the active filter comprises an amplifier and a transformer configured to filter out common-mode signals on the first and second differential input/output conductors.

11. A method of coupling a physical layer transceiver, in a radiofrequency (RF) wireline communications system, between a differential wireline channel medium and a functional device, the physical layer transceiver being an integrated circuit device having first and second differential wireline conductors configured for coupling to the differential wireline channel medium, and having first and second differential input/output conductors extending toward the functional device, the method comprising:

terminating a first one of the first and second differential input/output conductors to a ground of the communications system between the physical layer transceiver and the functional device;

coupling a second one of the first and second differential input/output conductors to a single-ended cable that is configured for coupling to the functional device; and

coupling a common-mode filter to both of the first and second differential input/output conductors, between the physical layer transceiver and the functional device, to filter out common-mode signals on the first and second differential input/output conductors.

12. The method of coupling a physical layer transceiver to a functional device according to claim 11 , wherein the physical layer transceiver integrated circuit device is mounted on a printed circuit board, and first and second differential signal traces on the printed circuit board are coupled to the differential input/output conductors; wherein:

terminating the first one of the first and second differential input/output conductors to the ground of the communications system comprises terminating a first one of the first and second differential signal traces to the ground of the communications system; and

coupling the common-mode filter to both of the first and second differential input/output conductors comprises coupling the common-mode filter to both of the first and second differential signal traces.

13. The method of coupling a physical layer transceiver to a functional device according to claim 12 , wherein a single-ended cable connector is mounted on the printed circuit board; the method further comprising:

coupling a second one of the first and second differential signal traces to the single-ended cable connector.

14. The method of coupling a physical layer transceiver to a functional device according to claim 13 wherein coupling the second one of the first and second differential input/output conductors to the single-ended cable comprises coupling a shielded single-ended cable to the single-ended cable connector.

15. The method of coupling a physical layer transceiver to a functional device according to claim 14 wherein coupling the shielded single-ended cable to the single-ended cable connector comprises coupling a coaxial cable to the to the single-ended cable connector.

16. The method of coupling a physical layer transceiver to a functional device according to claim 11 wherein the physical layer transceiver integrated circuit device comprises an integrated circuit die mounted on a substrate; the method comprising:

forming the common-mode filter, that is coupled to both of the first and second differential input/output conductors, on the integrated circuit die.

17. The method of coupling a physical layer transceiver to a functional device according to claim 11 wherein the physical layer transceiver integrated circuit device comprises an integrated circuit die mounted on a substrate; the method comprising:

forming the common-mode filter, that is coupled to both of the first and second differential input/output conductors, on the substrate, to filter out common-mode signals on the first and second differential input/output conductors.

18. The method of coupling a physical layer transceiver to a functional device according to claim 11 wherein coupling the common-mode filter to both of the first and second differential input/output conductors comprises coupling a common-mode choke to both of the first and second differential input/output conductors to filter out common-mode signals on the first and second differential input/output conductors.

19. The method of coupling a physical layer transceiver to a functional device according to claim 11 wherein coupling the common-mode filter to both of the first and second differential input/output conductors comprises coupling an active filter to both of the first and second differential input/output conductors to filter out common-mode signals on the first and second differential input/output conductors.

20. The method of coupling a physical layer transceiver to a functional device according to claim 19 wherein coupling the active filter to both of the first and second differential input/output conductors comprises coupling an amplifier and a transformer to both of the first and second differential input/output conductors.