1. Field of the Invention
The present invention relates to high performance multi-pair data cables, and more particularly, to multi-pair cables using different twist lay lengths and pair proximity control to meet category six performance specifications.
2. Discussion of Related Art
As is known in the art, cables formed from twisted pairs of insulated conductors are used to transfer communication signals between, for example, components of a local area network (LAN) such as computers, telephones, and other devices. The TIA/EIA-568A specification sets out transmission requirements, such as, for example, maximum acceptable crosstalk, skew and impedance mismatch values between twisted pairs, for cables that are classified as Category 5 (Cat. 5) and category 6 (Cat. 6) cables. In order to meet these requirements various techniques are employed to control crosstalk between twisted pairs and skew.
Referring to
As can be seen with reference to
In reality, the pair arrangement in a conventional four pair cable, after assembly, is more likely to resemble the configuration shown in
According to one embodiment, a multi-pair cable may comprise four twisted pairs of insulated conductors each having a respective unique twist lay length, thereby providing six twist deltas between the twist lay lengths of the four twisted pairs, wherein at least five of the six twist deltas are greater than 15%.
According to another embodiment, a multi-pair cable may comprise a first twisted pair of conductors having a first twist lay length, and a second twisted pair of conductors having a second twist lay length that is shorter than the first twist lay length, wherein the first and second twisted pairs of conductors are in physical contact with one another along substantially an entire length of the multi-pair cable, and wherein a difference between the first twist lay length and the second twist lay length is at least 15% of the second twist lay length. In one example, the first and second twisted pairs may be nested to form a central core of the multi-pair cable having two interstices, and at least one dielectric filler may be disposed in one of the two interstices of the central core.
The foregoing and other features and advantages of the present invention will be apparent from the following non-limiting discussion of various illustrative embodiments and aspects thereof with reference to the accompanying figures. It is to be appreciated that the figures are provided as examples for the purposes of illustration and explanation and are not intended as a definition of the limits of the invention. In the figures, in which like elements are represented by like reference numerals,
a is a schematic cross-sectional diagram of a related art cable;
b is a schematic cross-sectional diagram of a related art cable;
a is a schematic cross-sectional diagram of one embodiment of a cable according to aspects of the invention;
b is a schematic cross-sectional diagram of another embodiment of a cable according to aspects of the invention;
Various illustrative embodiments and examples of the present invention and aspects thereof will now be described in more detail with reference to the accompanying figures. It is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Other applications, details of construction, arrangement of components, embodiments and aspects of the invention are possible. Also, it is further to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. As used herein, a “multi-pair cable” comprises two or more twisted pairs of insulated conductors contained within a cable jacket. The term “twist lay length” as used herein refers to the distance along the length of a twisted insulated conductor pair for a complete revolution of the individual conductors around each other, and the term “twist delta” refers to a difference in twist lay length between different twisted insulated conductor pairs within the multi-pair cable. For the purposes of this specification, an “aggressive” twist delta between two pairs is defined as a twist delta between two pairs of a cable, before cabling all the twisted pairs together, of greater than 15%, i.e., a twist lay length of one of the two twisted pairs is at least 15% larger than a twist lay length of the other of the two twisted pairs. In some embodiments, an aggressive twist delta also comprises a twist delta of greater than 15% between two pairs of a cable after cabling of the cable. Also, the term “crosstalk” refers to both Near End Crosstalk (NEXT) and Power Sum Crosstalk (PSUM NEXT), and the term “skew” refers to a difference in a phase delay added to the electrical signal for each of the plurality of twisted pairs of the multi-pair cable. In addition, the use of “including,” “comprising,” or “having” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
Referring to
According to one embodiment, the twisted pairs of the multi-pair cable of
Of course it is also to be appreciated that the values given in Table 2 are simply examples and a cable may be constructed according to the principles of the invention using different twist lay lengths for each twisted pair. Such twist lay lengths can be readily determined by one of skill in the art based on this disclosure.
In contrast to the conventional cable illustrated in
In a four-pair cable there are six possible combinations of pairs and thus six twist deltas. As discussed above, a conventional cable, such as illustrated in
According to one aspect of the invention, the two nested pairs 40, 46 may be twisted with shorter twist lay lengths than those of the twisted pairs 42, 44. Twisted pairs with short twist lay lengths are more inclined to nest because, in order to partially compensate for skew, twisted pairs with short twist lay lengths, e.g., twisted pair 40, may be constructed using slightly heavier copper for the metallic conductors 48 and having a slightly larger outer diameter than do the conductors 48a of, for example, twisted pair 42. Thus, because the twisted pairs 40, 46 may be larger and heavier than the twisted pairs 42, 44, the twisted pairs 40, 46 may nest. This aspect, combined with the rotational aspect discussed above with reference to
As discussed above, the Cat. 6 specification requires a maximum skew between twisted pairs in the cable 52 of 45 ns per 100 m over a frequency range of approximately 0.77 MHz to 250 MHz. In addition, the Cat. 6 specification requires that the minimum crosstalk isolation between twisted pairs of the cable 52 be about 44 dB per 100 m at a test frequency of 100 MHz. For a cable according to the invention having the example twist lay lengths given in Table 2, the minimum crosstalk isolation between twisted pairs may be approximately 46 dB at 100 MHz and the maximum skew may be approximately 39 ns per 100 m for the specified frequency range of 0.77–250 MHz. Thus, using the novel twist lay schemes and pair proximity control of the invention, an unshielded twisted pair cable that meets the Cat. 6 performance requirements may be provided without a central filler or cross-web. This is a significant advantage over prior art cables since a cable that does not require the additional filler may be cheaper to manufacture and more likely to meet plenum requirements.
According to another embodiment of the invention, a four-pair cable, such as illustrated in any of
Referring to
According to another embodiment of the invention, a multi-pair cable may be provided with one or more dielectric fillers that may be used to separate twisted pairs from one another and to add to the structural stability of the cable. For example, referring to
Another example of a multi-pair cable including dielectric fillers is illustrated in
Various illustrative examples of multi-pair cables according to aspects of the invention have been described above in terms of particular dimensions and characteristics. However, it is to be appreciated that the invention is not limited to the specific examples described herein and the principles may be applied to a wide variety of shielded and unshielded multi-pair cables. The above description is therefore by way of example only, and includes any modifications and improvements that may be apparent to one of skill in the art. For example, any or all of the twisted pairs in any of the configurations illustrated in
This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application Ser. No. 60/445,255, filed Feb. 5, 2003, entitled “Multi-pair Communication Cable Using Different Twist Lay Lengths and Pair Proximity Control.”
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