Communications plugs and patch cords with mode conversion control circuitry

1. A patch cord comprising:

a communications cable that includes first through eighth conductors, wherein the fourth and fifth conductors are twisted together to form a first twisted pair, the first and second conductors are twisted together to form a second twisted pair, the third and sixth conductors are twisted together to form a third twisted pair, and the seventh and eighth conductors are twisted together to form a fourth twisted pair; and

a plug that is attached to the communications cable, the plug comprising:

a housing that receives the communications cable;

first through eighth plug contacts;

a printed circuit board that is at least partly within the housing, the printed circuit board including first through eighth conductive paths that connect the first through eighth conductors to the respective first through eighth plug contacts; and

a first crosstalk injection circuit between the second conductive path and the sixth conductive path; and

a second crosstalk injection circuit between the first conductive path and the sixth conductive path.

2. The patch cord of claim 1 , wherein the first and second crosstalk injection circuits substantially cancel the common mode crosstalk injected from the third twisted pair onto the second twisted pair when the third twisted pair is excited differentially.

3. The patch cord of claim 1 , further comprising a third crosstalk injection circuit between the second conductive path and the third conductive path.

4. The patch cord of claim 3 , wherein the first, second and third crosstalk injection circuits substantially cancel the common mode crosstalk injected from the third twisted pair onto the second twisted pair when the third twisted pair is excited differentially.

5. The patch cord of claim 1 , further comprising a third crosstalk injection circuit between the first conductive path and the third conductive path.

6. The patch cord of claim 5 , wherein the first, second and third crosstalk injection circuits substantially cancel the common mode crosstalk injected from the third twisted pair onto the second twisted pair when the third twisted pair is excited differentially.

7. The patch cord of claim 1 , wherein the first crosstalk injection circuit comprises a first capacitor on the printed circuit board between the second conductive path and the sixth conductive path.

8. The patch cord of claim 6 , wherein the second crosstalk injection circuit comprises a second capacitor on the printed circuit board between the first conductive path and the sixth conductive path.

9. The patch cord of claim 8 , wherein the first capacitor connects to the second conductive path directly adjacent the second plug contact and connects to the sixth conductive path directly adjacent the sixth plug contact.

10. The patch cord of claim 1 , wherein the first through eighth plug contacts include plug contact regions that are substantially aligned in a row in numerical order.

11. An RJ-45 communications plug that has first through eighth conductive paths where the fourth and fifth conductive paths are part of a first differential transmission line, the first and second conductive paths are part of a second differential transmission line, the third and sixth conductive paths are part of a third differential transmission line, and the seventh and eighth conductive paths are part of a fourth differential transmission line, wherein the first, third, fifth and seventh conductive paths are tip conductive paths and the second, fourth, sixth and eighth conductive paths are ring conductive paths, the plug comprising:

a housing;

first through eighth plug blades that are at least partially within the housing and that are electrically connected to the respective first through eighth conductive paths, the first through eighth plug blades aligned in a row in numerical order;

an offending crosstalk circuit that is separate from the plug blades that injects crosstalk between the second and third differential transmission lines, where the offending crosstalk circuit is between a ring conductive path and a tip conductive path; and

a differential-to-common mode crosstalk cancellation circuit that is electrically connected between the second differential transmission line and the third differential transmission line.

12. The RJ-45 communications plug of claim 11 , wherein the differential-to-common mode crosstalk cancellation circuit substantially cancels common mode crosstalk that is injected within the plug from the third differential transmission line to the second differential transmission line when the third differential transmission line is excited differentially.

13. The RJ-45 communications plug of claim 11 , wherein the differential-to-common mode crosstalk cancellation circuit includes a first reactive circuit between the second conductive path and the sixth conductive path, a second reactive circuit between the first conductive path and the sixth conductive path and a third reactive circuit between the second conductive path and the third conductive path.

14. The RJ-45 communications plug of claim 13 , wherein the first reactive circuit comprises a first capacitor on a printed circuit board, the second reactive circuit comprises a second capacitor on the printed circuit board and the third reactive circuit comprises a third capacitor on the printed circuit board.

15. The RJ-45 communications plug of claim 14 , wherein the first capacitor connects to the second conductive path directly adjacent to a signal injection location on the second plug blade, and connects to the sixth conductive path directly adjacent to a signal injection location on the sixth plug blade.

16. The RJ-45 communications plug of claim 11 , wherein differential crosstalk injected onto the second transmission line by the third differential transmission line when the third differential transmission line is excited differentially is greater than twice amount of coupling between the second plug blade and the third plug blade minus twice the amount of coupling between the first plug blade and the third plug blade.

17. The RJ-45 communications plug of claim 11 , further comprising a communications cable that has first through eighth conductors that are electrically connected to the respective first through eighth conductive paths to provide a patch cord.

18. The RJ-45 communications plug of claim 11 , wherein the offending crosstalk circuit comprises a capacitor, the RJ-45 communications plug further comprising a resistor coupled in series with the capacitor.

19. The RJ-45 communications plug of claim 11 , wherein the differential-to-common mode crosstalk cancellation circuit comprises a capacitor, the RJ-45 communications plug further comprising a resistor coupled in series with the capacitor.

20. An RJ-45 communications plug that has first through eighth conductive paths that are arranged as first through fourth differential transmission lines, the plug comprising:

a housing;

first through eighth plug blades that are at least partially within the housing and that are electrically connected to the respective first through eighth conductive paths; and

a capacitor and a resistor electrically coupled in series between two of the first through eighth conductive paths.

21. The RJ-45 communications plug of claim 20 , wherein the capacitor is implemented on a printed circuit board of the plug and the resistor comprises a surface mount resistor on the printed circuit board.

22. The RJ-45 communications plug of claim 20 , wherein the series resistor and capacitor are interposed between the second conductive path and the sixth conductive path.