Electricity: conductors and insulators – Conduits – cables or conductors – Insulated
Reexamination Certificate
2000-05-25
2001-11-27
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Insulated
Reexamination Certificate
active
06323427
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a cable made of twisted wire pairs, and more particularly to a cable made of twisted wire pairs that is suitable for use in high-speed data communication applications.
BACKGROUND OF THE INVENTION
One method of transmitting data and other signals is by using twisted wire pair cables. A twisted wire pair cable includes at least one pair of insulated conductors twisted about one another to form a two conductor pair. In practice, most network applications use cables with both solid and stranded conductors. A number of methods known in the art may be employed to arrange and configure the twisted wire pairs into various high-performance transmission cable arrangements. Once the twisted pairs are configured into the desired “core,” a plastic jacket is typically extruded over them to maintain their configuration and to function as a protective layer. When more than one twisted pair group is bundled together, the combination is referred to as a multi-pair cable.
In cabling arrangements where the conductors within the wires of the twisted wire pairs are stranded, two different, but interactive sets of twists can be present in the cable configuration. First, there is the twist of the wires that make up the twisted wire pair. Second, within each individual wire of the twisted wire pair, there is the twist of the wire strands that form the conductor. Taken in combination, both sets of twists have an interrelated effect on the data signal being transmitted through the twisted wire pairs.
With multi-pair cables, the signals generated at one end of the cable should ideally arrive at the same time at the opposite end even if they travel along different twisted pair wires. Measured in nanoseconds, the timing difference in signal transmissions between the twisted wire pairs within a cable in response to a generated signal is commonly referred to as “delay skew.” Problems arise when the delay skew of the signal transmitted by one twisted wire pair and another is too large and the device receiving the signal is not able to properly reassemble the signal. Such a delay skew results in transmission errors or lost data.
Moreover, as the throughput of data is increased in high-speed data communication applications, delay skew problems can become increasingly magnified. Even the delay in properly reassembling a transmitted signal because of signal skew will significantly and adversely affect signal throughput. Thus, as more complex systems with needs for increased data transmission rates are deployed in networks, a need for improved data transmission has developed. Such complex, higher-speed systems require multi-pair cables with stronger signals, and minimized delay skew.
A number of factors can contribute to the timing differences in signal propagation or skew along different twisted wire pairs in a data transmission cable, each of which may have different lay lengths. Such factors include: the amount or degree of twist or “lay length” of each cable; the geometric configurations of the twisted wire pairs and the cable; the chemical and physical properties of the materials used; and the amount or degree of twist or “lay length” in the wire strands that form the individual conductors of the twisted wire pairs. To better distinguish the “lay length” of the twisted wire pairs from that of the wire strands of the conductors, the lay length of the wire strands will hereinafter be referred to as the “strand twist length.”
When twisted wire pair cable s are used in connection with high-speed data communication applications, controlling the various factors that affect signal propagation becomes increasingly important. Thus, there is a need for a twisted wire pair cable that addresses the limitations of the prior art to effectively control and minimize delay skew within multi-pair cables.
SUMMARY OF THE INVENTION
The present invention recognizes that a number of factors contribute to differences in the signal propagation along different twisted wire pairs of a multi-pair cable. For instance, when other factors are the same, a signal from a twisted pair with a shorter twist length or lay length can potentially arrive much later than the signal sent through a twisted pair with a longer twist length or lay length. This is primarily due to the fact that an increased length of wire is needed to provide a shorter lay length, or, in other words, more wire is needed to provide a shorter, or “tighter,” twist length over a given length of cable. Likewise, the same principle holds true for the twisted wire strands that form the conductor of a stranded conductor.
Standard test methods using commercially available instruments can determine the signal propagation characteristics of a twisted wire pair. One example of such an instrument is a network analyzer, which can determine the difference in phase between the signals of twisted wire pairs. Phase delay is a measurement of the amount of time that a simple sinusoidal signal is delayed when propagating through the length of a twisted wire pair. The delay skew or “skew” is the difference in the phase delay value of two twisted wire pairs. In multi-pair cables having more than two twisted wire pairs, the skew value is represented by the maximum difference in phase delay between any two twisted wire pairs.
To address the problem of delay skew, the present invention correlates several important factors that affect the transmission throughput of the twisted pairs to effectively minimize delay skew and improve the timing between the pairs of the cable. In particular, the present invention focuses on designing and constructing low skew multi-pair cables wherein the twisted wire pairs have different lay lengths and/or strand twist lengths.
In accordance with the teachings of the present invention, the physical properties of the twisted wire pairs affecting signal propagation in a multi-pair cable are taken into account and a multi-pair cable suitable for high-speed data transmission is provided in which the lay lengths of the twisted wire pairs and strand twist lengths of the wire conductors within the twisted wire pairs are correlated and appropriately matched to reduce the associated amount of delay skew. Therefore, a multi-pair cable having features of the present invention includes an outer jacket and at least two pairs of twisted wire cables having different lay lengths and being encased within the jacket. The wires of each twisted wire pair have a conductor surrounded by an insulating material, wherein the conductors of the respective twisted wire pairs have different strand twist lengths. The lay lengths of the twisted wire pairs are correlated with the strand twist length of the conductors of the individual twisted wire pairs so that the phase delay of the twisted wire pairs of the cable is matched to within an acceptable range for data transmission. Conversely, where the lay lengths of the twisted wire pairs is predetermined, the strand twist lengths of the respective conductors of the individual twisted wire pairs can be correlated with the lay lengths of the twisted wire pairs so that the phase delay of the twisted wire pairs of the cable is brought to within an acceptable range for the intended application.
By way of example, when all other factors are approximately the same, a wire with a conductor comprised of wire strands which has a comparably short strand twist length relative to the strand twist length of the other twisted pairs will be included in a twisted pair which has a comparably long lay length. Conversely, a wire with a stranded conductor which has a comparatively long strand twist length will be included in a twisted pair which has a comparatively short lay length. The amount of delay skew is significantly reduced by utilizing longer strand twist length with the tightly twisted pair and a shorter twisted strand twist length with the longer twisted pair because the signal travel path length, measured as “impedance” (or alternatively, as “capacitance”) is nearly equal between pairs. By applying this me
Krone Inc.
Nguyen Chau N.
Rader & Fishman & Grauer, PLLC
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