JP5863156B2 - Differential signal transmission cable - Google Patents

Description

  The present invention relates to a differential signal transmission cable.

  As a conventional technique, a pair of insulated wires arranged in parallel is further arranged in parallel with at least one drain conductor, and the pair of insulated wires and the drain conductor are collectively wrapped with a metal foil tape to be shielded. 2. Description of the Related Art A parallel two-core shielded electric wire that is a conductor and whose outer periphery is covered with a jacket is known (for example, see Patent Document 1).

  Since the parallel two-core shielded electric wire described in Patent Document 1 forms a shield conductor by winding a metal foil tape, the manufacturing time can be shortened.

JP 2002-289047 A

  In the parallel two-core shielded electric wire according to Patent Document 1, a flat portion of the metal foil tape is produced in the cross section in the short direction. In this flat part, the direction of the tension of the metal foil tape and the surface created by the surface of the flat part are parallel to each other, so that the pressure for pressing the metal foil tape based on the tension is not generated and the metal foil tape is loosened. It becomes easy. The conventional parallel two-core shielded electric wire has a problem that skew and differential common-mode conversion amount increase due to looseness of the metal foil tape.

  Accordingly, an object of the present invention is to provide a differential signal transmission cable that suppresses skew and differential common-mode conversion.

  In order to achieve the above-mentioned object, the present invention has a pair of conductors arranged in parallel apart from each other, a shape that covers the pair of conductors, and a combination of a plurality of curves having different curvature radii in the outer peripheral shape of the cross section in the short direction. And a shape in which the inner peripheral shape of the cross section in the short direction is a combination of a plurality of curves based on the outer peripheral shape of the insulator. A shield conductor covering the shield conductor, the shield conductor has a metal foil facing the cover member, and the insulator has an elliptical outer peripheral shape in the cross section The minimum value of the radius of curvature of the plurality of curves is 1/20 or more and 1/4 or less of the maximum value of the radius of curvature of the plurality of curves, and the minor axis of the cross section is 0. 37 times or more 0.63 times or more To provide a differential signal transmission cable is.

  In the above differential signal transmission cable, the covering member is preferably a braid.

  In the differential signal transmission cable, the insulator is preferably formed using a foam material.

  The differential signal transmission cable preferably has a layer having a lower foaming degree than the inside on the outside.

  According to the differential signal transmission cable of the present invention, it is possible to suppress the skew and the differential common-mode conversion amount.

FIG. 1 is a perspective view of a differential signal transmission cable according to the first embodiment. 2A is a cross-sectional view of the differential signal transmission cable according to the first embodiment cut in the short direction, and FIG. 2B is a cross-sectional view of the differential signal transmission cable cut in the short direction. It is a schematic diagram. Fig.3 (a) is a schematic diagram which shows the relationship between the tension | tensile_strength T and the pressure P at the time of winding a press-wound tape around the insulated wire whose cross section which concerns on the comparative example 1 becomes circular shape, (b) is a comparison. It is a schematic diagram which shows the relationship between the tension | tensile_strength T and the pressure P at the time of winding a pressing tape around the insulated wire which has the flat part which concerns on Example 2. FIG. FIG. 4 is a diagram illustrating a relationship between the radius of curvature of the differential signal transmission cable according to the first embodiment and the probability that the metal foil tape is loosened. FIG. 5A is a cross-sectional view in the short-side direction of the differential signal transmission cable according to the second embodiment, and FIG. 5B is a graph regarding the maximum value and the minimum value of the radius of curvature. FIG. 6 is a cross-sectional view of the differential transmission cable according to the third embodiment. FIG. 7 is a perspective view of a differential signal transmission cable according to a modification.

[Summary of embodiment]
The cable for differential signal transmission according to the embodiment combines a pair of conductors arranged in parallel apart from each other, and a plurality of curves that cover the pair of conductors, and whose outer peripheral shape of the cross section in the short direction has a different radius of curvature. An insulator having a shape, and a shield conductor that is provided by being wound around the insulator and has a shape in which an inner peripheral shape of a cross section in a short direction is a combination of a plurality of curves based on the outer peripheral shape of the insulator.

(Outline of the configuration of the differential signal transmission cable 1)
FIG. 1 is a perspective view of a differential signal transmission cable according to the first embodiment. 2A is a cross-sectional view of the differential signal transmission cable according to the first embodiment cut in the short direction, and FIG. 2B is a cross-sectional view of the differential signal transmission cable cut in the short direction. It is a schematic diagram. Two circles indicated by dotted lines in FIG. 2B are illustrated for ease of explanation, and a cable having a cross-sectional shape in the short direction similar to that of the differential signal transmission cable 1 is created. The cross-sectional shape of the insulated wire used is shown. Hereinafter, unless otherwise specified, the cross section indicates a cross section cut in the short direction.

  The differential signal transmission cable 1 is, for example, a differential signal transmission cable between or in electronic devices such as servers, routers, and storages using differential signals of 10 Gbps or more.

  In this differential signal transmission, signals having a phase difference of 180 ° are transmitted to the respective conductors in a pair of conductors, and the difference between the two signals having different phases is extracted on the receiving device side. Since the currents flowing through the pair of conductors flow in opposite directions, the electromagnetic waves radiated from the conductor that is the transmission path through which the current flows are reduced. Further, in differential signal transmission, noise received from the outside is equally superimposed on the two conductors, and therefore noise can be removed by taking the difference.

  The differential signal transmission cable 1 according to the present embodiment, for example, as shown in FIG. 1, covers a pair of conductors 2 (conductors) arranged in parallel and apart, and a pair of conductors 2, An insulator 3 having a shape in which the outer peripheral shape of the cross section is a combination of a plurality of curves having different curvature radii, and the inner peripheral shape of the cross section in the short direction is based on the outer peripheral shape of the insulator 3. In addition, a metal foil tape 7 as a shield conductor having a shape formed by combining a plurality of curves is provided and schematically configured.

  Moreover, the differential signal transmission cable 1 according to the present embodiment includes, for example, a presser winding tape 8 as a covering member coated with a metal foil tape 7, and the metal foil tape 7 is connected to the plastic tape 5 as an insulating member. And a metal foil 6 as a conductive film provided on the surface opposite to the surface facing the insulator 3 of the plastic tape 5 (that is, the surface facing the presser winding tape 8).

  The conducting wire 2 is, for example, a single wire of a good electric conductor such as copper, or a single wire obtained by plating the electric conductor. Moreover, the radius r of the conducting wire 2 is 0.511 mm, for example. Furthermore, the space | interval L of the conducting wire 2 and the conducting wire 2 is 0.99 mm, for example. This interval L indicates the interval between the center of the conducting wire 2 and the center of the conducting wire 2 in the cross section of the conducting wire 2. For example, when the bending characteristic is important, the conducting wire 2 may be a stranded wire formed by twisting a plurality of conducting wires.

  The insulator 3 is formed using, for example, a material having a small dielectric constant and dielectric loss tangent. This material is, for example, polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), polyethylene or the like. The insulator 3 may be formed using a foam insulating resin as a foam material in order to reduce the dielectric constant and the dielectric loss tangent. For example, when the insulator 3 is formed using a foamed insulating resin, a foaming agent is kneaded into the resin, a method of controlling the degree of foaming according to the temperature at the time of molding, a gas such as nitrogen is injected at a molding pressure, It is formed using a method of foaming at the time of release.

For example, as shown in FIG. 2B, the insulator 3 has a substantially elliptical cross-sectional shape. As an example, the width W _{1 in the} major axis direction is 2.8 mm, and the width W _{2 in the} minor axis direction is 1. .54 mm.

  The insulator 3 has, for example, a region 30 (region indicated by hatching) surrounded by the insulator 3 and a surface connecting the vertices of two circles indicated by dotted lines in FIG. The circle indicated by the dotted line is, for example, a circle inscribed on the outer periphery of the cross section of the insulator 3. For example, when the two circles indicated by dotted lines in FIG. 2B are insulated wires, the region 30 indicates a region that is not formed in the insulator covering the two insulated wires. As an example, the maximum width t of the region 30 is 0.07 mm. Hereinafter, the cross-sectional shape of the insulator 3 will be further described with reference to Comparative Example 1 and Comparative Example 2.

  Fig.3 (a) is a schematic diagram which shows the relationship between the tension | tensile_strength T and the pressure P at the time of winding a press-wound tape around the insulated wire whose cross section which concerns on the comparative example 1 becomes circular shape, (b) is a comparison. It is a schematic diagram which shows the relationship between the tension | tensile_strength T and the pressure P at the time of winding a pressing tape around the insulated wire which has the flat part which concerns on Example 2. FIG.

  Here, since the differential signal transmission cable transmits a high-speed signal of several Gbps, it is necessary to reduce the skew. This skew indicates a time difference in arrival time between differential signals (that is, skew within a pair).

  For example, when a cable is formed using two insulated wires, the skew is a slight difference in dielectric constant of the insulator, a slight difference in outer diameter of the insulator, and a drain wire attached in the longitudinal direction of the insulator. This occurs due to a slight deviation or a gap formed at the interface between the insulator and the metal foil tape due to the looseness of the metal foil tape provided outside the insulator.

  Moreover, since the differential signal transmission cable needs to reduce EMI (Electro-Magnetic Interference), it is necessary to keep the differential common-mode conversion amount low. If the (right / left) symmetry of the cable is not good, a part of the input differential signal is converted into an in-phase signal. This ratio of conversion to in-phase is called differential in-phase conversion amount. In particular, the ratio of the in-phase signal appearing at port 2 to the differential signal at port 1 can be measured as an S parameter and is represented by “Scd21”.

  As a method for reducing the skew, a method is known in which two conductors are covered together with one insulator to suppress a dielectric constant difference between the insulators. As another method, before covering the two insulated wires with the conductor for shielding, the insulating tape is wound and the distance between the shield and the conductor is relatively increased, so that the electromagnetic coupling between the conductors is achieved. A method is also known in which the cable is strengthened and is less likely to cause skew.

  The above-described method for reducing the skew is confirmed to have a certain effect on the skew caused by the dielectric constant difference inside the insulator, so that the outer peripheral shape of the insulator is constant and the conductor is not displaced. In combination with this, the skew can be reduced.

  However, the effect of the air gap caused by the looseness of the metal foil tape wound around the insulator remains slightly even if the above measures are taken. For example, when the differential signal transmission cable is used as a high-speed signal transmission cable corresponding to 10 Gbps, there is a problem in that the yield decreases due to the influence of the air gap.

  The looseness of the metal foil tape occurs, for example, in any case where the metal foil tape is wound around an insulator or when the metal foil tape is vertically attached and the presser tape is wound.

  The cause of loosening of the wound metal foil tape is, for example, that the force with which the metal foil tape presses the insulator, that is, the pressure P applied to the insulator by the metal foil tape is small.

  As shown in FIG. 3A, in the case of Comparative Example 1 in which the metal foil tape 101 is wound around the insulated wire 100 having a circular cross section, the insulated wire 100 has a force so as to balance the tension T of the metal foil tape 101. Works.

This force becomes the pressure P applied to the side surface of the insulated wire 100, and this pressure has a relationship expressed by P = T / (2wr ₁ ) (w: width of the metal foil tape, r ₁ : radius of the insulated wire). Have.

On the other hand, as shown in FIG. 3B, in the case of the comparative example 2 in which the metal foil tape 101 is wound around the insulated wire 102 whose cross section is a combination of the flat portion 103 and the curved portion 104, the curved portion 104 includes: The same pressure as P indicated by P = T / (2wr ₁ ) is applied. However, in the flat portion 103, the direction of the tension T of the metal foil tape 101 and the surface formed by the surface of the flat portion 103 are parallel, so the pressure P applied to the flat portion 103 based on the tension T is It becomes zero.

  Here, the metal foil tape 101 is either a cross-sectional shape formed by arranging two circular insulated wires side by side or a cross-sectional shape obtained by combining the curved portion 104 and the flat portion 103 as shown in FIG. When the wire is wound, there is a portion where the metal foil tape 101 is linear in the cross section.

  That is, in the case of the comparative example 2, when the metal foil tape 101 is wound, the tension T of the metal foil tape 101 and the surface formed by the surface of the flat portion 103 are parallel, so that force acts on the flat portion 103. do not do. In the flat portion 103, the metal foil tape 101 to be wound is loosened due to a slight movement of the differential signal transmission cable when the metal foil tape 101 is wound, a slight change in the tension of the metal foil tape 101, and the like. As a result, skew occurs and the differential common-mode conversion amount increases.

  Based on the above results, the insulator 3 according to the present example has regions 30 which are hatched portions shown in FIG. 2B above and below the paper surface of FIG. Therefore, the vector of the pressure P generated by winding the metal foil tape 7 eliminates a portion where the direction of the tension T of the metal foil tape 7 and the surface formed by the surface of the flat portion 103 are parallel.

  The plastic tape 5 of the metal foil tape 7 is formed using a resin material such as polyethylene, for example.

  The metal foil 6 of the metal foil tape 7 is formed, for example, by bonding copper or aluminum to one surface of the plastic tape 5.

  The metal foil tape 7 has a seam or an overlapping region along the longitudinal direction of the insulator 3. For example, the metal foil tape 7 according to the present embodiment is cigarette-wound so as to cover the insulator 3 of the insulated wire 4. The cigarette winding is a method in which the metal foil tape 7 is attached in the longitudinal direction of the insulator 3 and the metal foil tape 7 is wound once from the side surface in the longitudinal direction of the insulator 3. The seam 70 shown in FIG. 1 is generated along the longitudinal direction when, for example, one end and the other end in the longitudinal direction of the metal foil tape 7 face each other. Moreover, when the metal foil tape 7 is longer than the outer periphery of the insulator 3 in the lateral direction, a region where one end portion and the other end portion of the metal foil tape 7 overlap is generated.

  The presser winding tape 8 is formed using, for example, a resin material.

  The presser winding tape 8 has a joint or overlapping portion on the metal foil tape 7 in a spiral shape. The presser winding tape 8 according to the present embodiment is wound in a spiral shape so as to cover the metal foil tape 7, for example. The presser winding tape 8 is wound around the insulator 3 so that one end portion and the other end portion in the short direction do not overlap each other. Accordingly, the seam 80 shown in FIG. 1 is formed in a spiral shape on the metal foil tape 7. Further, when the presser winding tape 8 is wound on the metal foil tape 7 so that one end and the other end thereof overlap each other, an overlapping region on the metal foil tape 7 is formed in a spiral shape.

Below, the manufacturing method of the cable 1 for differential signal transmission which concerns on a present Example is demonstrated.
(Manufacturing method of the differential signal transmission cable 1)
First, a pair of conducting wires 2 are covered with an insulator 3 to produce an insulated wire 4. Specifically, the conducting wires 2 are separated and arranged in parallel. As an example, the pair of conductive wires 2 are arranged in parallel with a separation of 0.99 mm. Moreover, the radius r of the conducting wire 2 is 0.511 mm as an example. Next, a pair of conducting wires 2 are covered with foamed polyethylene to form an insulator 3. The insulator 3 is formed by adjusting the foaming degree so that the relative dielectric constant of the insulator 3 is 1.5 as an example.

The shape of the insulator 3 has a shape composed of a plurality of curves having different radii of curvature as shown in FIG. 2B. As an example, the width W _{1 in the} major axis direction is 2.8 mm, and the minor axis direction. The width W ₂ is 1.54 mm. Here, the maximum width t of the region 30 is 0.07 mm as an example. As an example, the radius of curvature of this region 30 is 7 mm.

  The insulator 3 is formed by, for example, producing an extrusion die for an extruder based on the shape of the insulation 3 and extruding foamed polyethylene together with a pair of conductors 2 from the extrusion die.

  Next, the metal foil tape 7 is attached to the longitudinal direction of the insulated wire 4, and the metal foil tape 7 is wound around the insulated wire 4. This winding is performed so that the plastic tape 5 side faces the insulator 3 and the metal foil 6 side is exposed to the outside. The metal foil 6 is exposed to the outside because soldering is performed in a later process.

Next, the presser winding tape 8 is wound around the metal foil tape 7 in a spiral shape, and after a predetermined process, the differential signal transmission cable 1 is obtained.
(Relationship between radius of curvature and looseness of metal foil tape 7)
FIG. 4 is a diagram illustrating a relationship between the radius of curvature of the differential signal transmission cable according to the first embodiment and the probability that the metal foil tape is loosened. In FIG. 4, the horizontal axis represents the radius of curvature, and the vertical axis represents the rate of looseness of the metal foil tape 7. The looseness occurrence rate of the metal foil tape 7 indicates a probability that a gap is generated between the insulator 3 and the metal foil tape 7 in a certain cable cross section in the entire produced cable.

  The rate of occurrence of looseness of the metal foil tape 7 is measured by the following method. First, a cable sample is extracted without deviating from the total length of the produced cable, and the cross section of the cable is observed. In each sample, it is confirmed whether or not there is a gap between the insulator 3 and the metal foil tape 7, and the ratio of the number of samples having a gap to the total number of samples is defined as a looseness occurrence rate.

  From the measurement results shown in FIG. 4, if the radius of curvature of the region 30 of the insulator 3 is 14 mm or less (20 times the radius of curvature of the curve located in the long axis direction), the looseness rate of the metal foil tape 7 is Thus, the performance of the differential signal transmission cable 1 can be maintained.

On the other hand, when the radius of curvature of the region 30 is 2.8 mm (four times the radius of curvature of the curve positioned in the major axis direction), the looseness rate of the metal foil tape 7 is reduced, but the thickness due to the region 30 is increased. It is about 0.25 mm. Due to this increase, the characteristic impedance of the differential signal transmission cable 1 increases. In addition, the differential signal transmission cable manufactured with a curvature radius of 2.8 mm has a large outer diameter of the cable in which a plurality of differential signal transmission cables face each other, and is difficult to handle. Therefore, the radius of curvature is preferably 4 to 20 times.
(Effect of Example 1)
According to the differential signal transmission cable 1 according to the present embodiment, the skew and the differential in-phase conversion amount can be suppressed. Specifically, as shown in FIG. 2B, the outer periphery of the cross section of the insulator 3 of the differential signal transmission cable 1 is a combination of a plurality of curves having different curvature radii, that is, the curvature radius is 0.7 mm. And a region 30 having a radius of curvature of 7 mm. Therefore, in the differential signal transmission cable 1, when the holding tape 8 is wound around the insulated wire 4, the pressure P is always applied to the surface of the insulator 3 so as to balance the tension T of the metal foil tape 7. If the tension T is constant, the pressure P is considered to be inversely proportional to the radius of curvature of the outer periphery of the cross section, so the pressure P in the region 30 drops to about 1/10 in the major axis direction. When not formed, the pressure P is not applied to the insulator in the straight line portion as described above.

  Moreover, since the area | region 30 is formed in the insulator 3 which concerns on a present Example, since the pressure P is always applied to the insulator 3, when winding the metal foil tape 7 around the insulator 3, the insulated wire 4 Even if the tape moves or the tension T of the presser winding tape 8 becomes weaker than a predetermined tension, the occurrence of looseness of the presser tape 8 can be suppressed. Therefore, since the looseness of the metal foil tape 7 can be suppressed, the formation of voids generated at the interface between the insulator 3 and the metal foil tape 7 can be suppressed. Therefore, the differential signal transmission cable 1 according to the present embodiment can suppress a decrease in performance due to an increase in skew and differential in-phase conversion amount.

  The second embodiment is different from the first embodiment in that the outer peripheral shape of the cross section in the short direction of the insulator 3 is an elliptical shape.

  FIG. 5A is a cross-sectional view in the short-side direction of the differential signal transmission cable according to the second embodiment, and FIG. 5B is a graph regarding the maximum value and the minimum value of the radius of curvature. In FIG. 5B, the horizontal axis is the x axis and the vertical axis is the y axis. In this ellipse, a major axis exists on the x-axis and a minor axis exists on the y-axis. In the following embodiments, portions having the same configurations and functions as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and description thereof is omitted.

  In the differential signal transmission cable 1 in the present embodiment, the outer peripheral shape of the insulator 3 is an elliptical shape having a focal point A and a focal point B. Other configurations are the same as those of the differential signal transmission cable 1 according to the first embodiment.

  In addition, the manufacturing method of the differential signal transmission cable 1 according to the present embodiment forms the insulator 3 having an elliptical shape having a major axis (= 2a) of 3.20 mm and a minor axis (= 2b) of 1.64 mm. This is different from the first embodiment.

  In the differential signal transmission cable 1 according to the present embodiment, the pressure P is always applied to the insulator 3 when the holding tape 8 is wound around the metal foil tape 7. Further, the vector of the pressure P applied to the insulator 3 by the metal foil tape 7 is directed to either the focal point A or the focal point B shown in FIG.

  When the tension T of the metal foil tape 7 is constant, the pressure P is inversely proportional to the radius of curvature of the outer periphery of the cross section of the insulator 3 as described above. Therefore, as shown in FIG. 4, when an equation representing an ellipse having a major axis 2a and a minor axis 2b is defined as equation (1), the radius of curvature at an arbitrary point (x, y) on the elliptic curve is expressed by equation (2). )

According to this equation (2), it can be seen that the radius of curvature changes in the range of b ² / a to a ² / b. Therefore, if the minimum value of the pressure P is (b / a) ³ times the maximum value, that is, the shape of this embodiment, the pressure P is reduced to about 13% on the short axis.

  However, since the differential signal transmission cable 1 according to the present embodiment can wind the metal foil tape 7 so that pressure is always applied to the insulator 3 as in the first embodiment, the metal foil tape 7 Even when the insulated wire 4 moves or the tension T of the presser tape 8 becomes weaker than a predetermined tension when wound around the insulator 3, the presser tape 8 can be prevented from loosening.

  As a result, loosening of the metal foil tape 7 can be suppressed, so that formation of voids generated at the interface between the insulator 3 and the metal foil tape 7 can be suppressed. Further, since there is no portion where the radius of curvature changes abruptly as compared with the first embodiment, the probability that a gap is generated becomes smaller. Therefore, the differential signal transmission cable 1 according to the present embodiment can suppress a decrease in performance due to an increase in skew and differential in-phase conversion amount.

The ratio between the minimum and maximum curvature radius is (b / a) ^{3 as} described above. Therefore, the range in which the radius of curvature is 1/20 or more and 1/4 or less is such that the minor axis of the cross section of the insulator 3 is 0.37 to 0.63 times the major axis, and the radius of curvature is within this range. If it fits, loosening of the metal foil tape 7 can be suppressed as in the first embodiment.

  Example 3 is different from the above examples in that the degree of foaming is different between the inside and the outer periphery of the insulator 3.

  FIG. 6 is a cross-sectional view of the differential transmission cable according to the third embodiment. In FIG. 6, a region surrounded by the outer periphery of the insulator 3 and a dotted line is an insulator layer 31.

  The differential signal transmission cable 1 in the present embodiment has different degrees of foaming inside and outside the insulator 3. Other configurations are the same as those of the differential signal transmission cable 1 according to the first embodiment. As an example, the foaming degree is 50% inside, and the insulator layer 31 is several percent.

  The insulating layer 31 of the insulator 3 has a lower foaming degree than the inside of the insulator 3. That is, since the insulator 3 is formed on the insulator 3, the outer peripheral portion is harder than the inside.

  Moreover, the manufacturing method of the differential signal transmission cable 1 according to the present embodiment covers the pair of conductors 2 using an extruder as in the first and second embodiments. 3 includes a step of extruding the outermost outer periphery 3 so as to recoat the insulating layer 31 having a small foaming degree. Other manufacturing methods are the same as those in the first and second embodiments.

According to the differential signal transmission cable 1 according to the present embodiment, the insulator layer 31 is formed on the outer peripheral portion as compared with the differential signal transmission cables of the first and second embodiments. Therefore, the pressure P received from the presser winding tape 8 acts on the insulator 3 more stably. As a result, loosening of the metal foil tape 7 can be suppressed, so that formation of voids generated at the interface between the insulator 3 and the metal foil tape 7 can be suppressed. Therefore, the differential signal transmission cable 1 according to the present embodiment can suppress a decrease in performance due to an increase in skew and differential in-phase conversion amount.
(Modification)
FIG. 7 is a perspective view of a differential signal transmission cable according to a modification. In the differential signal transmission cable 1 according to the modification, the metal foil tape 7 has a joint 80 spirally on the insulator 3, and the covering member that covers the metal foil tape 7 is the braid 9. This metal foil tape 7 is obtained by bonding a metal foil 6 made of copper to one surface of a plastic tape 5, and the braid 9 is made of 64 copper strands having a strand diameter of 0.08 mm. is there.

  In the differential signal transmission cable 1 according to this modification, since the insulator 3 has the shape described in any one of the first to third embodiments, the metal foil tape 7 is wound in a spiral shape. Also, the occurrence of looseness can be suppressed. As a result, the formation of voids generated at the interface between the insulator 3 and the metal foil tape 7 can be suppressed. Therefore, the differential signal transmission cable 1 according to the present modification can suppress a decrease in performance due to an increase in skew and differential in-phase conversion amount.

  Note that the metal foil tape 7 may have a spiral region overlapping the insulator 3.

  As mentioned above, although embodiment, Example, and its modification of this invention were described, embodiment, Example, and modification which were described above do not limit the invention which concerns on a claim. In addition, it should be noted that not all the combinations of features described in the embodiments, examples, and modifications are essential to the means for solving the problems of the invention.

DESCRIPTION OF SYMBOLS 1 ... Cable for differential signal transmission 2 ... Conductor 3 ... Insulator 4 ... Insulated electric wire 5 ... Plastic tape 6 ... Metal foil 7 ... Metal foil tape 8 ... Pressing tape 9 ... Braid 30 ... Area 31 ... Insulator layer 70 ... Seam 80 ... Seam 100 ... Insulated wire 101 ... Metal foil tape 102 ... Insulated wire 103 ... Flat part 104 ... Curve part

Claims (8)

A pair of conductors spaced apart in parallel;
An insulator that covers the pair of conductors and has a shape that combines a plurality of curves in which the outer peripheral shape of the cross section in the short direction has a different curvature radius;
A shape in which the inner peripheral shape of the cross section in the short direction is combined with the plurality of curves based on the outer peripheral shape of the insulator is provided so as to spirally have a seam or an overlapping region on the insulator. A shield conductor,
A covering member covering the shield conductor;
The shield conductor has a metal foil facing the covering member,
In the insulator, the outer peripheral shape of the cross section has an elliptical shape, and the minimum value of the curvature radius of the plurality of curves is 1/20 or more and 1/4 or less of the maximum value of the curvature radius of the plurality of curves. In addition, a differential signal transmission cable in which the minor axis of the cross section is not less than 0.37 times and not more than 0.63 times the major axis.   The differential signal transmission cable according to claim 1, wherein the covering member is formed using a resin material and is wound around the shield conductor in a spiral shape.   The differential signal transmission cable according to claim 1, wherein the covering member is a braid.   The differential signal transmission cable according to claim 1, wherein the insulator is formed using a foam material.   The cable for differential signal transmission according to claim 4, wherein the insulator has a layer having a lower foaming degree than the inside.   The cable for differential signal transmission according to claim 1, wherein the shield conductor has an insulating member facing the insulator.   The differential signal transmission cable according to claim 1, wherein the metal foil is made of copper.   The differential signal transmission cable according to claim 1, wherein the differential signal transmission cable is used for transmitting a differential signal of 10 Gbps or more.