EP0871182A1 - High data rate flat signal transmission cable - Google Patents

Abstract

The flat cable is constructed using an extruded section base (10), which has channels between flanges (12). Insulated conductors (20) are placed in the channels which are dimensioned to provide a tight fit. Each conductor in a pair of conductors is individually twisted such that the length of a complete turn is much shorter than the wavelength of the signals to be transmitted. The surfaces of the channels are made conducting and the conductors (20) are covered with a metallic foil. The cable is completed with an enveloping sheath.

Description

The present invention relates to a flat cable of high-speed signal transmission comprising at least one pair of conductive wires.

We already know flat cables used in IT in the form of a sheet made of material plastic in which several conductors are coated parallel. These cables are made by extruding the plastic coating simultaneously around all the drivers. Sometimes the plastic coating material is applied to already insulated conductors. We observe that the conductors are relatively badly centered because it is very difficult to achieve precise positioning of all the conductors in such an extruded sheet. In Consequently, these cables can only be used on a short length, which does not exceed a few tens of centimeters, and at relatively low frequencies, in general of the order of a few kilohertz but practically always below 10 MHz. However, we prefer use these ribbon cables when their use is possible because the regular arrangement of conductors allows the use of a simple insulation displacement connection whose implementation is very fast.

We also know, from the patent of the United States America No. 3,663,739, a ribbon cable in which the positioning of the conductive wires relative to the others may be better. According to this document, a profile is made with ribs which delimit grooves. The surface of grooves and profiles is coated with a member ground conductor, and insulated conductors are housed in the gorges due to a common thread throat. The grooves are then closed, preferably by a additional conductive member. So each wire conductor can be considered as screened separately.

Such a flat cable, which can be used with a simple insulation displacement connection, however presents disadvantage. Indeed, if the shielding of the conducting wires separated allows a reduction in crosstalk thanks to the electromagnetic protection obtained, there is an effect capacitive between the conductors when these are poorly centered in their insulator.

This drawback is described in detail because it limits the frequencies at which the ribbon cable can be used. In this flat cable, there is a capacity between each conductor and the mass coating formed on the grooves and the ribs. If all the drivers were fine equidistant from this ground plane, it would not exist capacitive effect of imbalance between the conductors. By against, as the drivers are always locally more or less off center in their own insulation, they have different capacitive effects from one conductor to another with respect to a ground plane. It then appears crosstalk phenomenon.

We also know, for the realization of networks premises, the use of twisted cables having multiple pairs of conductive wires. These cables avoid crosstalk the main cause of which is imbalances capacitive between pair conductors different, the conductors and the mass. Imbalances capacitive are reduced by the effect of the twists which give symmetry. However, these twisted cables have a very significant disadvantage because they don't allow the use of an insulation displacement connection, so that the costs of connecting and installing these cables are same order of magnitude as the cost of cables and their connectors. In addition, the laying of these twisted cables is inconvenient in apparent along the partitions because they have a great thickness.

The invention aims to allow the use of flat cables for the realization of local networks having great lengths, of the order of 100 m, with flow rates high, at frequencies up to 100 MHz. In this indeed, the invention implements means which reduce the capacitive effects of shielded flat cables, on the one hand, by twisting each solid conductor and, on the other hand, by association of the conductors of each pair so let them be closer to each other than sons conductors of other pairs.

More specifically, the capacitive effects presented by each conductor with respect to the ground plane are compensated by using twisted conductors each on himself. Then the cross-talk effects between conductors of different pairs are reduced by more great closeness of conductors of the same pair as conductors belonging to different pairs.

Thus, the subject of the invention is a flat cable of high speed signal transmission comprising at least a pair of conductor wires each having a conductor and an insulator, a profile having at least one delimited groove by ribs, and a mass conducting member placed at the less on the surface of each groove, characterized in that it has two individually twisted conductors, each one on itself with a step much less than the length wave corresponding to the frequency of the signals to transmit, and thus kept juxtaposed in the same throat.

In an advantageous embodiment, the pitch of twist varies from one conductor to another by the same pair and / or along the length of each thread, but it is always between 10 and 50 mm.

In an exemplary embodiment, the conductive member of mass is a metallic ribbon surrounding each pair. In one another embodiment, the mass conducting member is a coating on the surface of grooves and ribs, for example formed by electroplating.

In a cable application, comprising at least two pairs of conductive wires and intended to be provided with a connector with insulation displacement contacts, the cable is such that the spacing of the two conductors of the same pair is significantly less than half the wire spacing conductors of different pairs.

la figure 1 représente un profilé métallisé contenant des fils conducteurs faisant partie d'un câble selon l'invention ;

la figure 2 représente un câble terminé réalisé avec le profilé de la figure 1 ;

la figure 3 représente une variante de profilé qui peut être utilisé dans un câble selon l'invention ; et

la figure 4 représente un détail de réalisation d'une variante de l'invention.

Other characteristics and advantages of the invention will emerge more clearly from the description which follows, given with reference to the appended drawings in which:

FIG. 1 represents a metallized section containing conductive wires forming part of a cable according to the invention;

2 shows a completed cable made with the profile of Figure 1;

FIG. 3 represents a variant of the profile which can be used in a cable according to the invention; and

Figure 4 shows a detail of an embodiment of the invention.

We first consider the capacitive phenomena between conductors. When a conductor is placed at a certain distance from a ground plane, there is a capacity between the conductor and the ground plane. When multiple drivers are placed at different distances from a plane of ground and transmit signals, the capabilities formed by each conductor and the ground plane are loaded. When the capabilities of different conductors are not the same, there appears an imbalance compared to the mass, and this imbalance creates a crosstalk called "by third circuit "; the capacitive imbalances of each of pairs with respect to mass create a coupling between them through this mass. During traffic of high frequency signals, this crosstalk phenomenon disturbs the signals of the various conductors. On the other hand, if all the capacities are identical, their imbalances compensate each other and no crosstalk tends to be established between neighboring conductors.

It is therefore important, to reduce imbalances capacitive causing crosstalk and to be able to use high frequencies at which these effects are significant and which can reach for example 100 MHz, to obtain capacities as equal as possible. We already know how to use very homogeneous materials and very regular diameters for insulating the conductive wires. However, it is not possible to achieve perfect centering of the conductor at inside its insulation. The invention makes it possible to remedy this disadvantage by using a twist of each conductor separated so that, by an effect of symmetry, the driver is, on average over a certain distance, perfectly centered in its insulation. In this way, taking into account the very constant diameter of the different conductors, the average distance between a conductor and a ground plane can be constant over the entire length of the common thread, and the capacities formed by each conductor with the ground plane have the same value, if although the capacitive crosstalk phenomena are deleted or at least significantly reduced.

So that this twist of the conductors ensures the removing at least most of the effects capacitive, the torsional pitch must be much lower at the wavelength at the frequencies used. By example, for the transmission of signals whose frequency reaches 100 MHz, a twisting pitch of less than 50 mm.

Consequently, according to an essential characteristic of the invention, the driver has been twisted. In one embodiment, this twist is introduced at the time where the conductor is made. However, given the high driver speeds in installations manufacturing industries it's hard to achieve such a twist. In another embodiment, the twist is given to the conductive wire, already having the insulation, for example at the entrance to a wire laying machine conductors in a cable profile according to the invention.

The conductor is preferably made of copper, having preferably 0.5 to 0.65 mm in diameter, and the wire conductor, including insulation, has a diameter of 1.2 to 2 mm, the insulation being made for example of polyethylene solid or cellular or any other material having a low dielectric constant (less than 3.5) and an angle loss less than 0.01 to 100 MHz.

Figure 1 shows a profile 10, for example formed from extruded polyvinyl chloride, which defines ribs 12 between which grooves are formed 14 intended to each house two conducting wires. In one embodiment, the profile has four grooves intended to accommodate four pairs of wires. However, it can include any number of grooves, and therefore pairs, a cable for local network can include two for example.

As shown in Figure 2, the grooves 14 include a conductive coating 16 which can be formed an added aluminum sheet, or a metallization performed for example by electroplating with ink conductive or by vacuum metallization. Leaf metallic or metallized polyester 18 is placed on the conducting wires 20 so that these are shielded. A sheath 22 surrounds the profile and the conducting wires. The total thickness of the cable is 2 to 3 mm in the example considered.

It is noted in FIGS. 1 and 2 that, in a mode of advantageous realization, the two conducting wires of each pair are grouped in a single groove. Preferably, the throat width is such that the two threads of the pair are tight against each other.

The conductors are individually twisted on themselves at a short twist, which varies from one of conductors to each other of the same pair and / or on their length. In this way, at each location of the cable length, the two conductors of each pair have a different step. Two conductors of the same pair are thus juxtaposed in the same groove, to give a better symmetry along their length and thus avoid crosstalk problems created by imbalances in the Earth.

In Figure 3, there is shown, in the case of a two pair cable only, ribs having overhanging projections in the grooves and allowing a better retention of conductive wires. In Figure 4, we indicated that each pair of lead wires could be coated with conductive tape 24, for example polyester metallized with aluminum, forming a conductive member mass, so that aluminum foil or metallization 16 on the one hand, and the metallic or polyester sheet metallized 18 on the other hand, which are represented in Figure 2 is no longer required.

The flat cables according to the invention have the advantage, given by all the flat cables, of being able to be connected by a connection with insulation displacement contacts which requires only a very short time to connect the various connected devices and accessories. Furthermore, when the cable has the arrangement shown in FIG. 1, that is to say when the two conductors of a pair are closer than those of adjacent pairs, the insulation displacement contacts intended to come and cooperate with two conductors of a pair are closer than contacts which cooperate with the conductors of pairs adjacent. In this way, the crosstalk phenomena at level of connectivity can be further reduced.

The flat cable according to the invention, when it has the features listed above, can be used for the installation of local networks conforming to specifications of class D networks according to standards ISO / IEC 11801 and EN 50173, i.e. usable on distances of the order of 100 m at frequencies of 100 MHz. The twist pitch of each conductor on itself is then between 10 and 50 mm.

1) qu'il n'est pas nécessaire de détorsader chaque paire et alors de connecter un à un les fils conducteurs, puisque des connecteurs autodénudants permettent une connexion presque instantanée par une main d'oeuvre peu qualifiée, si bien que le coût de main d'oeuvre qualifiée est considérablement réduit, et

2) qu'il est possible de disposer le câble à plat contre les murs et cloisons d'une manière commode et esthétique, par exemple par collage, avec un faible encombrement en épaisseur.

The main advantages of the cable according to the invention compared to the twisted pair cables currently used in the application considered, are

1) that it is not necessary to untwist each pair and then to connect the conductive wires one by one, since insulation displacement connectors allow an almost instantaneous connection by an unskilled workforce, so that the cost of labor of skilled work is considerably reduced, and

2) that it is possible to arrange the cable flat against the walls and partitions in a convenient and aesthetic manner, for example by gluing, with a small bulk in thickness.

It is understood that the invention has not been described and shown only as a preferred example and that may provide any technical equivalence in its constituent elements without departing from its framework.

Claims (6)

Flat cable for high speed signal transmission, comprising at least one pair of conducting wires (20) having each a conductor and an insulator, a profile (10) having at minus a groove (14) delimited by ribs (12), and a mass conducting member (16) placed at least on the surface of each groove, characterized in that it comprises two wires conductors (20) twisted individually, each on itself with a step much less than the wavelength corresponding to the frequency of the signals to be transmitted, and thus kept juxtaposed in the same groove (14). Cable according to claim 1, intended for transmission of signals whose frequency is of the order of 100 MHz or less, characterized in that the twisting pitch of each thread is between 10 and 50 mm. Cable according to either of Claims 1 and 2, characterized in that the twisting pitch varies from one of the wires to each other in the same pair and / or on the length of each thread, always understood between 10 and 50 mm. Cable according to one of Claims 1 to 3, characterized in that the mass conducting member (24) is a metallic ribbon surrounding each pair. Cable according to one of Claims 1 to 3, characterized in that the mass conducting member (16) is coating the surface of the grooves and ribs. Cable according to any one of claims 1 to 5, comprising at least two pairs of conducting wires, characterized in that the spacing of the two conducting wires of the same pair is significantly less than half of the spacing of the conducting wires of different pairs.

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