Electricity: conductors and insulators – With fluids or vacuum – Conduits – cables and conductors
Reexamination Certificate
2000-02-18
2001-12-04
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
With fluids or vacuum
Conduits, cables and conductors
C174S1130AS
Reexamination Certificate
active
06326542
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of reducing “skew” in data carrying cables, and to cables and data installation in which the method of the present invention is used to reduce skew to an acceptable level.
For the purposes of data transmission, cables comprising a plurality of pairs of conductors are frequently used. Each conductor is separately insulated and each pair of conductors is twisted together to form a so-called “twisted pair”. The “twist-rate” (that is the number of twists per unit length) of each pair is deliberately different from that of each other pair so as to reduce cross-talk between the pairs. The effect of this variation in twist rate is that for any given length of cable the length of the conductors forming each twisted pair will be different from the length of conductors forming each other twisted pair. As a result of this length variation, signals applied simultaneously to the twisted pairs at one end of the cable will arrive at different times at the other end of the cable. This characteristic is known as “skew”.
By way of example, the transit time for signals injected simultaneously on two different pairs of a typical commercial Category 5 (100 MHz) cable containing four twisted pairs and a length of 100 m may typically vary by 20 ns (20 nano seconds). Such variation in transit time renders cables of this length unacceptable for high frequency data transmission, and in particular, such cables are totally unacceptable for so-called “gigabit ethernet” systems.
With a view to avoiding this problem, special cables have been produced for high speed data transmission. Such cables are of complex construction and typically include individually shielded conductors which are bonded together in a manner in eliminate length variations of the conductors within a given length of cable. Such cables are expensive and difficult to use because of their limited flexibility and because of the relative complexity of forming terminations on the cables.
SUMMARY OF THE INVENTION
We have now devised a method which substantially reduces or eliminates skew between the twisted pairs of a conventional cable which incorporates a plurality of twisted pairs, for example, a conventional Category 5 data cable.
A method of reducing or eliminating skew between signals of first and second conductors of a data cable, the method comprising steps of transferring the signal of the first conductor from the first conductor to the second conductor at a position intermediate the ends of the data cable and transferring the signal of the second conductor from the second conductor to the first conductor at a position intermediate the ends of the data cable, the transferring of the signals being such that, in travelling the length of the cable, any one of said signals travels partly on the first conductor and partly on the second conductor, wherein the first and second conductors each comprise a twisted pair of first conductors and a twisted pair of second conductors.
REFERENCES:
patent: 6066799 (2000-05-01), Nugent
patent: 0 556 579 (1993-08-01), None
patent: 7-209563 (1995-08-01), None
patent: WO 97 27679 (1997-07-01), None
Dykema Gossett PLLC
Nguyen Chau N.
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