EP2467857A1

EP2467857A1 - Data communication cable

Info

Publication number: EP2467857A1
Application number: EP10761050A
Authority: EP
Inventors: Thomas Haehner; Tony Droguest; Gilles Routa; Patrick Rofidal; Jean-François GALLET
Original assignee: Nexans SA
Current assignee: Nexans SA
Priority date: 2009-08-19
Filing date: 2010-08-12
Publication date: 2012-06-27
Also published as: CN102473484A; CN105321624A; WO2011020967A1; FR2949274A1; US20120186846A1; FR2949274B1; KR20120041249A

Abstract

The subject of the invention is a data communication cable, characterized in that it comprises; a plurality of groups (1,2,3,4) of four pairs of insulated conductors, the four pairs of insulated conductors being assembled as a helix with a group assembly pitch, each pair being helically twisted and surrounded by an electric shielding (9, 10), the plurality of groups (1,2,3,4) being assembled as a helix with a final assembly pitch, an exterior sheath (8) surrounding the plurality of groups (1,2,3,4), the final assembly pitch being variable along the cable.

Description

DATA COMMUNICATION CABLE

The present invention relates to data communication cables comprising a plurality of groups of four pairs of individually isolated conductors for high speed data transmission.

An electrical cable typically includes one or more sets of twisted wires. An assembly conventionally consists of two twisted conductive wires. In this case we speak of a pair of conductors.

Crosstalk, tele-crosstalk or para-crosstalk, refers to the electromagnetic interference between assemblies belonging to the same electric cable. Exogenous crosstalk refers to the electromagnetic interference between assemblies belonging to different electrical cables. The phenomenon of crosstalk is frequently a problem for data transmission.

To greatly reduce crosstalk, it is known to twist the conductive wires between them in a helix, and preferably with a different pitch from one assembly to another, and to surround each pair of an electrical shield to reduce electromagnetic coupling. This arrangement makes it possible to transport high frequencies, in particular for applications up to several tens of Gb / s.

In order to accommodate more pairs of conductors in the same space, and thus make the outside diameter of the cable as small as possible, it is advantageous to arrange the pairs of conductors in groups of four pairs of conductors.

If geometric variations are repeated periodically in the cable, a problem that may arise is the appearance of reflection peaks of the signal, corresponding to a weak reflection loss. These peaks appear at certain frequencies which correlate with the periodicity of the geometric variation.

These peaks are undesirable because they increase noise and can lead to an increase in line attenuation along the cable, ie peaks reduce the signal-to-noise ratio and can reduce the throughput. data transmission. It is known to shift the peaks to higher frequencies by decreasing the group assembly pitch.

This solution however has the disadvantage that the assembly is longer to achieve, requires more driver and labor and is more expensive.

The invention aims to remedy these drawbacks.

The invention thus relates to a data communication cable comprising:

a plurality of groups of four pairs of insulated conductors, the four pairs of insulated conductors being helically assembled in a group assembly pitch, each pair being helically twisted and surrounded by an electrical shield, the plurality of groups being assembled in a helix according to a final assembly step,

an outer sheath surrounding the plurality of groups.

According to the invention, the final assembly pitch is variable along the cable.

This variation of the pitch of the final assembly makes it possible to avoid periodic variations in the geometry of the cable and thus represents an economical and productive alternative to the reduction of the group assembly pitch.

The cable may not include any sheath other than the outer sheath. Thanks to the absence of ducts surrounding each group, the cable is lighter, less bulky and contains less flammable material.

The group assembly pitch can also be variable along the cable.

In this case, the final assembly step and / or the group assembly step advantageously varies between two limit values of the same sign.

The final assembly step and / or the group assembly step may vary according to a periodic function, for example a sinusoidal function.

The final assembly pitch and / or group assembly pitch may also vary randomly.

For ease of assembly, the cable preferably comprises three, four or six groups. According to a first embodiment, each group comprises an electrical shielding pair of insulated conductors.

According to a second embodiment, each group comprises a single electrical shield in the form of a cross.

The cross can separate the pairs of conductors from each other and surround each pair of conductors.

Other characteristics and advantages of the present invention will appear more clearly on reading the following description given by way of illustrative and nonlimiting example and with reference to the appended drawings in which:

FIG. 1 is a sectional view of a cable of the state of the art,

FIG. 2 is a sectional view of a cable according to the invention, according to a first embodiment,

FIG. 3 is a sectional view of a cable according to the invention, according to a second embodiment, and

- Figures 4 and 5 are two diagrams useful for understanding the invention.

A cable of the state of the art is illustrated in FIG. 1. The cable, of circular section, comprises four groups 1 to 4 of four pairs of insulated conductors, the pairs of which are individually shielded.

The conductors of the pairs are identical. Each conductor comprises a conductive core 6, typically copper, and a peripheral insulation 7. The two electrical conductors of each pair are directly helically assembled to each other by twisting and thus have a step called no pairing.

Each group 1 to 4 of four pairs of insulated conductors is surrounded by a protective sheath 5, generally made of polymer material. The assembly formed by the four groups 1 to 4 thus surrounded is itself surrounded by an outer protective sheath 8.

However, such a cable has the disadvantage of being heavy, of large volume and of presenting flammable materials.

The cable illustrated in FIGS. 2 and 3 is of circular section. The elements identical to those of Figure 1 bear the same references. The cable illustrated in Figure 2 differs from the cable of Figure 1 in that it has no intermediate sheaths surrounding each group of four pairs of insulated conductors. In this embodiment, the cable thus comprises a single sheath 8, which is the outer sheath constituting the outer portion of the cable.

The non-presence of the intermediate sheaths advantageously makes it possible to limit the weight, the dimensions and the quantity of flammable material in the cable.

The pitch of each pair of insulated conductors may or may not be constant along the cable.

Each group 1,2,3,4 may comprise a first pair having a first pairing step, a second pair having a second pair step, a third pair having a third pairing step and a fourth pair having a fourth pairing step. . In the same group 1,2,3,4, the first step of the pairing, the second step of pairing, the third step of pairing and the fourth step of pairing can be different, so as to reduce the crosstalk between the pairs.

The first step of pairing can be identical in all groups 1,2,3,4. In the same way, the second step of pairing can be identical in all the groups 1,2,3,4, the third step of pairing can be identical in all the groups 1,2,3,4, and the fourth step of Pairing can be identical in all groups 1,2,3,4.

Groups 1-4 of four pairs of insulated conductors can be electrically shielded in two different ways. According to a first embodiment, as illustrated in FIG. 2, a metallic or metallized ribbon 9 is helically ribboned around each pair of insulated conductors. Then, the four individually shielded pairs are helically assembled to form a group. The pitch of the helix formed by the assembly of the four pairs of conductors is called no group assembly. The final helical assembly of the four 1,2,3,4 groups is then carried out. The pitch of the helix formed by the assembly of the four groups 1,2,3,4 of four pairs of conductors is called no final assembly. The group assembly step can be the same for all groups 1,2,3,4 or may not be the same for all groups 1,2,3,4.

For the cable connection, the individual shields of the pairs must be removed for access to the conductors, making the connection operation long and delicate.

To facilitate the connection operation, and in accordance with a second embodiment illustrated in FIG. 3, the electrical shields of the different pairs of each group 1, 2, 3, 4 are constituted by a central rod 10 in the shape of a cross provided with radial fins, separating the pairs from each other and surrounding each pair, so as to shield each of them. As for the first embodiment, a cable provided with such a shield has a very low cross-talk, which makes it compatible with high-speed transmissions. It is also easy and fast to equip a terminal connector, since to access the conductors of the pairs simply draw the cable to a suitable length and to remove the peripheral shield on this length, then to cut the rod 10, which represents a significant time saving. The risk of damaging the conductors or disturbing the arrangement of the pairs is also greatly avoided when mounting the connector.

These peaks are undesirable because they increase noise and can lead to an increase in line attenuation along the cable, ie peaks reduce the signal-to-noise ratio and can reduce the throughput. data transmission.

Thus, for a mean pairing pitch of 50 mm and a group assembly pitch of 180 mm, a signal reflection peak is observed for a signal frequency of about 650 MHz (and its multiples) and for a frequency about 1300 MHz (and its multiples). Peak at 650 MHz is caused by the group assembly step, while the peak at 1300 MHz is caused by the step of pairing.

Similarly, there is an increase in line attenuation for a signal frequency of about 650 MHz (and its multiples) and for a frequency of about 1300 MHz (and its multiples). The peak at 650 MHz is caused by the cluster pitch, while the peak at 1300 MHz is caused by the step of pairing.

It is known to shift the peaks to higher frequencies by decreasing the group assembly pitch. It is thus observed that the peaks described above are observed at a frequency of 1.35 GHz (and its multiples) if the group assembly pitch is 85 mm instead of 180 mm.

To remedy this, and according to the invention, the final assembly pitch varies along the cable. This variation of the pitch of the final assembly makes it possible to avoid periodic variations in the geometry of the cable and thus represents an economical and productive alternative to the reduction of the assembly pitch.

Indeed, the final assembly pitch is ideally 600 mm but it creates a peak at 200MHz (and its multiples) and disrupts the data transmission, while the group assembly pitch can be set at 100 mm and create a peak around 1200MHz, beyond the frequency range of the desired application. In this case, the final assembly pitch is varied while keeping the group assembly pitch constant.

It is furthermore possible to vary the pitch along the cable, in addition to varying the grouping pitch along the cable.

Figures 4 and 5 illustrate two embodiments of variation of the group assembly step along the cable.

According to a first embodiment, as illustrated in FIG. 4, the group assembly pitch is between two limit values, for example between 160 and 200 mm, and varies randomly. Not group assembly is shown as a function of the distance at the end of the cable.

According to a second embodiment, as shown in FIG. 5, the group assembly pitch is between two limit values, for example between 160 and 200 mm, and varies sinusoidally, with a random period. The group assembly pitch is also shown as a function of the distance at the end of the cable.

In the same way, it is also conceivable to vary the final assembly step randomly, or sinusoidally with a random period. The final assembly step and the group assembly step may each vary randomly, or sinusoidally with a random period.

Claims

Data communication cable, characterized in that it comprises: a plurality of groups (1, 2, 3, 4) of four pairs of insulated conductors, the four pairs of insulated conductors being assembled in a helix according to a step of group assembly, each pair being helically twisted and surrounded by an electrical shield (9, 10), the plurality of groups (1, 2, 3, 4) being helically assembled in a final assembly step, a sheath outer (8) surrounding the plurality of groups (1,2,3,4), the final assembly pitch being variable along the cable.

2. Cable according to claim 1, characterized in that the cable comprises no other sheath than the outer sheath (8).

3. Cable according to claim 1 or 2, characterized in that the group assembly step (1,2,3,4) is variable along the cable. 4. Cable according to claim 3, characterized in that the final assembly pitch and / or the group assembly pitch (1,2,3,

4) varies between two limit values of the same sign.

5. Cable according to claim 3 or 4, characterized in that the final assembly pitch and / or the group assembly step (1,2,3,4) varies according to a periodic function.

6. Cable according to claim 3 or 4, characterized in that the final assembly pitch and / or the group assembly step (1,2,3,4) varies randomly.

7. Cable according to one of claims 1 to 6, characterized in that it comprises three, four or six groups (1,2,3,4).

8. Cable according to one of claims 1 to 7, characterized in that each group (1,2,3,4) comprises an electrical shield (9) by pair of insulated conductors.

9. Cable according to one of claims 1 to 7, characterized in that each group (1,2,3,4) comprises a single electrical shield (10) in the form of a cross.

10. Cable according to claim 9, characterized in that the cross (10) separates the pairs of conductors from each other and surrounds each pair of conductors.