Data cable

Abstract

A data cable for high-speed data transmission at signal frequencies of >10 GHz includes at least one core pair which is surrounded by a film-shaped pair shield having an inner shielding film and an outer shielding film which, are in electrical contact with one another and in which the inner shielding film is wound around the core pair. By virtue of this measure, an undesired resonance effect is avoided which, in previously wound pair shields, has not allowed use for relatively high signal frequencies. At the same time, an undesired common-mode signal, which would occur in the case of a longitudinally folded shielding film, is thus suppressed.

Claims

1. A data cable for high-speed data transmissions, the data cable comprising: at least one core pair formed of two cores; and a film-shaped pair shielding defining a fully-enclosed shielding surrounding said at least one core pair, said pair shield including an inner shielding film and an outer shielding film, said inner and outer shielding films being in mutual electrical contact, said outer shielding film being wound around said inner shielding film with gaps, and said inner shielding film being wound around said at least one core pair with an overlap; said inner shielding film has a width, and said overlap of said inner shielding film lies within a range between 20% and 40% of said width of said inner shielding film; said outer shielding film has a width, and said gaps of said outer shielding film are each equal to between 1 and 10% of said width of said outer shielding film.

2. The data cable according to claim 1, wherein: said at least one core pair includes a plurality of core pairs; said pair shielding is one of a plurality of pair shieldings each surrounding a respective one of said core pairs; and each of said pair shieldings includes two respective shielding films.

3. The data cable according to claim 2, which further comprises fixing films each being wound around a respective one of said plurality of pair shieldings.

4. The data cable according to claim 2, which further comprises: a cable core including a plurality of conductors; said plurality of conductors each including a respective one of said core pairs and a respective one of said pair shieldings; and an outer shielding surrounding said cable core.

5. The data cable according to claim 1, wherein said cores are mutually parallel.

6. The data cable according to claim 1, wherein said inner shielding film is wound around said at least one core pair with no gaps.

7. The data cable according to claim 1, wherein at least said inner shielding film has a multi-layer configuration and includes a conductive layer and a substrate.

8. The data cable according to claim 1, wherein said inner and outer shielding films each have a respective conductive layer and a respective substrate, and said conductive layers face inwardly toward each other.

9. The data cable according to claim 1, wherein said outer shielding film and said inner shielding film are wound in opposite directions.

10. The data cable according to claim 1, which further comprises a wire bonded to at least one of said shielding films, said wire being disposed between said shielding films or outside of said outer shielding film.

11. The data cable according to claim 1, which further comprises a fixing film wound around said pair shielding.

12. The data cable according to claim 1, which further comprises: a cable core including a plurality of conductors; one of said conductors including said core pair and said pair shielding; and an outer shielding surrounding said cable core.

13. The data cable according to claim 1, wherein said inner and outer shielding films are two different films wrapped around said at least one core pair.

14. A data cable assembly for high-speed data transmissions, the data cable assembly comprising: a cable core including a plurality of conductors; said plurality of conductors each including a respective one of said core pairs and a respective one of said pair shieldings according to claim 1; and an outer shielding surrounding said cable core.

15. The data cable according to claim 1, wherein said inner shielding film is wound directly around said at least one core pair.

16. The data cable according to claim 1, wherein said inner shielding film is only one inner shielding film and said outer shielding film is only one outer shielding film.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a diagrammatic, cross-sectional view of a core pair, fitted with a pair shielding;

(2) FIG. 2 is a side-elevational view of the core pair represented in FIG. 1;

(3) FIG. 3 is an enlarged, longitudinal-sectional view of the pair shielding in an overlap zone;

(4) FIG. 4 is an enlarged, cross-sectional view of a data cable according to a first embodiment variant;

(5) FIG. 5 is a cross-sectional view of a data cable according to a second embodiment variant; and

(6) FIG. 6 is a diagram in which insertion damping I is plotted against frequency f in GHz for different pair shieldings in a symmetrical core pair.

DETAILED DESCRIPTION OF THE INVENTION

(7) Referring now in detail to the figures of the drawings, in which components of equivalent function are identified by the same reference numbers, and first, particularly, to FIG. 1 thereof, there is seen a core pair 4 for use in a high-speed data cable 2 (see FIGS. 4 and 5), with a pair shielding 6. The core pair 4 in this case includes two cores 8, each of which in turn includes a central conductor 10, which is surrounded by insulation 12. The conductor 10 is customarily a solid conductor. Alternatively, stranded wires can also be used.

(8) The two cores 8 are preferably configured in a mutually parallel configuration, and are consequently not twisted together.

(9) The core pair 4 as a whole is surrounded by a multi-layered pair shielding, which includes an inner shielding film or foil 14 and an outer shielding film or foil 16. Specifically, these two shielding films 14, 16 form a closed configuration of the pair shielding 6. Finally, the pair shielding 6 is enclosed and is specifically wound within a fixing film or foil 18, which is specifically configured as an adhesive film. The fixing film 18 is formed of plastic, and is electrically non-conductive, and thus electrically insulating.

(10) Additionally, FIG. 1 includes an exemplary representation of an optional sheath wire 20, which is preferably disposed in an intermeshing zone of the two cores 8. The sheath wire 20 is moreover specifically disposed between the two shielding films 14, 16. Alternatively, two sheath wires 20 are preferably externally bonded to the outer shielding film 16, as represented e.g. in FIG. 5. The two sheath wires 20 are disposed on an imaginary plane of symmetry or connecting line of the two conductors 10. In the event of the external positioning of the at least one sheath wire 20, the latter is therefore specifically held between the outer shielding film 16 and the fixing film 18.

(11) The core pair 4, together with the pair shielding 6 and the fixing film 18 and, where applicable, the sheath wires 20, are also described hereinafter as a shielded pair 30.

(12) The two shielding films 14, 16 are preferably each metal-coated plastic films, specifically Al-PET films. These films are each provided with a substrate 22, configured as an insulating layer, to which a conductive layer 24 is applied (see in this respect specifically FIG. 3). In the event of the external positioning of the sheath wires, the outer side of the outer shielding film 16 must also be configured as a conductive layer 24. The outer shielding film 16 is then, for example, a substrate 22 with conductive layers 24 applied to both sides, or a metal film which, in principle, has conductive layers 24 on either side.

(13) The two shielding films 14, 16 are oriented in such a way that their respective conductive layers 24 are mutually inward-facing, and specifically are in mutual contact, in such a way that the two conductive layers 24 are bonded in an electrically conductive configuration.

(14) As can be seen in FIG. 2, the inner shielding film 14 is helically wound around the core pair 4. The shielding film 14 is customarily wound with a very small pitch, i.e. in a very close-wound configuration. The smaller the pitch, the greater the displacement of the unwanted resonance effect to higher frequencies. Typically, the pitch is only a few mm, for example on the order of 2 to 6 mm, i.e. for each 360 winding, the shielding film advances by 2 to 6 mm in the longitudinal direction 28.

(15) The inner shielding film 14 is wound with an overlap 26, in such a way that adjoining winding sections are mutually overlapped in the longitudinal direction 28. According to a preferred configuration, this overlap 26 is equal to approximately one third of the width B of the inner shielding film 14.

(16) The outer shielding film 16 is also preferably wound, but in the opposite direction to the inner shielding film 14. The outer shielding film 16 is, for example, disposed with the same pitch as the inner shielding film 14. Alternatively, the pitch thereof differs from that of the latter and is, for example, smaller or even greater. The outer shielding film 16 can also be provided with an overlap, or can be wound in a butt-jointed configuration.

(17) In a preferred configuration, however, a gapped winding is provided, in such a way that a clearance A is formed between two adjoining winding sections. The clearance A, for example, lies within the range of 1-5% of the width B of the outer shielding film 16.

(18) The fixing film 18 is specifically a plastic substrate film, to which an adhesive layer is applied. This film is also preferably wound in a manner not shown in FIG. 2.

(19) With reference to the enlarged sectional representation of the pair shielding 6 in an overlap zone shown in FIG. 3, it will be seen that the inner shielding film 14, in its mutually opposing edge zones, and consequently in the overlap zone 26, is disposed with the conductive layer 24 facing outwards. Therefore, the inner shielding film 14 is not enclosed at the edge zones. In the overlap zone 26, the inner shielding film 14 is thus disposed in an alternating sequence of the substrate 22 and the conductive layer 24. Accordingly, the edge zones of the conductive layer 24 of the inner shielding film 14 are separated in a mutually insulated manner in the overlap zone 26, thereby resulting in the above-mentioned oscillating circuit with the unwanted resonance effect whereby, specifically at higher frequencies in excess of 5 GHz, unwanted damping occurs as a result of the resonance effects. Due to the additional provision of the outer shielding film 16 described herein, these unwanted effects are at least reduced. At the same time, the overlap 26 selected in the exemplary embodiment shown in FIG. 3 damps the unwanted common mode signal.

(20) Customarily, in a data cable 2, a plurality of conductors 30 are combined in a cable core 32, as represented in FIGS. 4 and 5. In both variants, each of the conductors includes a shielded pair 30. However, other types of conductors can also be incorporated.

(21) The two variants of the data cable 2 represented in FIGS. 4 and 5 are mutually distinguished specifically with respect to the composition of the individual shielded pairs 30. In the variant represented in FIG. 4, shielded pairs 30 of the type described with reference to FIG. 1 are used.

(22) In the variant represented in FIG. 5, an alternative embodiment is employed. In this case, two sheath wires 20 are disposed externally between the outer shielding film 16 and the fixing film 18.

(23) In both variants it is preferred that two shielded pairs 30 are firstly wound in a plastic film, as represented in the exemplary embodiment. This core area is then circumferentially enclosed by a plurality of further shielded pairs 30. In the exemplary embodiment the further shielded pairs 30 are six in number.

(24) These shielded pairs, and consequently the cable core 32, are preferably enclosed in a multi-layer sheathing configuration. In data cables 2 of this type, the cable core 32 is generally surrounded by a common outer shield 34. In the exemplary embodiment, an additional inner layer of plastic film is also wound around the cable core 32.

(25) In the exemplary embodiment, the outer shield 34 is configured in a multi-layer configuration, including a combination of film or foil shielding 36 and, for example, braided shielding 38. Finally, this outer shield 34 is enclosed in a common cable sheath 40.

(26) FIG. 6 shows the insertion damping I of various shielded pairs of different types, plotted against the frequency f of the data signal being transmitted (in GHz). Curves A and B represent conventional embodiment variants. Curve A represents a shielded pair which is only surrounded by a single-layer shielding film. Conversely, curve B represents a shielded pair which is surrounded by a longitudinally folded shielding film.

(27) Curve B also represents a characteristic trend for a winding variant in which the inner film 14 is wound with only a small overlap 26, as described heretofore.

(28) Curve C is a characteristic curve for a variant associated, for example, with the shortest possible pitch of an Al-PET film, e.g. associated with the use of a 26 AWG (American Wire Gauge) wire. Through the use of an extremely short winding, the critical frequency can thus be displaced to a higher frequency band.

(29) Curve D is a characteristic curve for the second variant described heretofore, in which the outer shielding film 16 is preferably wound in a gapped configuration, with a small clearance A on the order, for example, of approximately 3% of the width of the shielding film 16, as described with reference to FIG. 2. At the same time, the inner shielding film 14 is preferably wound with a large overlap 26 on the order, for example, of approximately 30% of its width.

(30) It will clearly be seen that, in a conventional core pair with a wound pair shielding (curve A), insertion damping shows a steep increase with effect from a signal frequency of approximately 5 GHz. Accordingly, the suitability of a data cable of that type for higher signal frequencies is still conditional.

(31) Conversely, a core pair 4 with a longitudinally folded shielding film (curve B), even at higher frequencies in excess of 5 GHz, shows a significantly smaller increase in damping, even in high-frequency ranges well in excess of 25 GHz. However, as mentioned at the outset, that is achieved at the expense of an unwanted increase in the common mode signal.

(32) Through the use of the special pair shielding 6 described herein, the insertion damping characteristic curve approximates more closely to the characteristic curve associated with a longitudinally folded pair shielding (curve B). A pair shielding 6 of this type, formed of the two shielding films 14, 16, even at higher frequencies in excess of 10 GHz, continues to show acceptable damping, so that a data cable 2 of this type is also suitable for the transmission of high-frequency data signals.

(33) Overall, the special construction of the pair shielding 6 described herein delivers the following advantages: the resonance effect (which acts as a type of band-stop filter) is inhibited, or is at least displaced to a significantly higher frequency band. At the same time, the effective suppression of the common mode signal is achieved by the overlapping 26. Overall, the disadvantages of a longitudinally folded pair shielding are significantly reduced while, at the same time, the unwanted resonance effect associated with spiral-wound shieldings is at least extended to a non-disturbing frequency range in excess of 10 GHz, and preferably in excess of 15 or 20 GHz. Helical winding also permits simpler manufacture. In longitudinally folded pair shieldings, the formation of films is associated with a high degree of wear. Moreover, overlaps generate asymmetry and, overall, the flexibility of pairs is reduced by longitudinal films. Moreover, there are disadvantages associated with the production of longitudinal films. Thus, a dedicated individual unit is required for each individual set of dimensions.