JP2017010707A - Signal cable for differential transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multicore cable for differential transmission in which skew fluctuation in a cable longitudinal direction is reduced in construction that performs differential signal transmission with coaxial electric wires of even numbers of equal to or greater than 4.SOLUTION: A multicore cable for differential transmission 1 includes coaxial electric wires of even numbers of equal to or greater than 4. A conductor cross-section area of the coaxial electric wires 20a-20d is 0.40 mmto 0.004 mm, and in a pair of the coaxial electric wires 20a-20d performing differential signal transmission, material and a dimension are mutually equal. A strand pitch of the coaxial electric wires 20a-20d is equal to or greater than 15 times of the aggregation external diameter of the aggregated coaxial electric wires 20a-20d in the multicore cable for differential transmission 1. The pair of the coaxial electric wires 20a-20d performing differential signal transmission is set up to become a diagonal line position of a polygon when the centers of the coaxial electric wires 20a-20d of the even numbers of equal to or greater than 4 are connected by straight lines.SELECTED DRAWING: Figure 1A

Description

  The present invention relates to a differential transmission multicore cable used for signal transmission of a high-speed digital signal or the like.

With the progress of information communication technology, the frequency band used for communication cables has expanded to the GHz band. As a multicore signal cable used as a transmission line when data transmission is performed at a high bit rate, there is a multicore cable for differential transmission using four or more coaxial wires.
For example, a multi-core cable for differential transmission using a 4-core coaxial cable has a configuration in which four coaxial cables are twisted together and an outer shield is arranged around the cable, and the circumference is covered with a jacket. Have.

  In such a multi-core cable for differential transmission, differential signal transmission is performed using a pair of coaxial cables, each paired with two coaxial cables. In this differential signal transmission, signals that are 180 degrees out of phase are simultaneously input to two coaxial cables and transmitted, and differential synthesis is performed on the receiving side. ing.

  However, differential signal transmission has a problem of signal degradation due to a delay time difference (skew) in signal transmission between two coaxial cables. For this reason, for example, Patent Document 1 discloses a technique for reducing skew by using two coaxial cables having the same cross-sectional shape and length as a pair and cutting each coaxial cable from the same cable. Has been.

JP 2004-1119060 A

  The skew in the differential transmission multi-core cable is determined by the physical length of the cable and the dielectric constant of the insulator of the cable. If these are the same in the two coaxial electric wires that form a pair, the skew is reduced. Generally, when transmitting differential signals with a multi-core cable for differential transmission, which is a multi-core assembly of four or more coaxial cables, the line length difference between the coaxial cables when manufacturing a multi-core cable for differential transmission When this occurs, the skew is adversely affected, and therefore, the pair of coaxial cables that perform differential signal transmission are arranged adjacent to each other in the multicore coaxial cable.

  In this case, when manufacturing a multi-core cable for differential transmission, the coaxial cables are uniformly gathered so that the cross-section of the arranged coaxial cables is uniformly circular so that there is no difference in line length between the multi-core coaxial cables. It is preferable to align so that it may fit inside. However, the multi-core cable for differential transmission may be pushed and its cross section may be crushed into an ellipse. In this case, there is a problem that a difference in line length occurs between coaxial cables that perform differential transmission, which adversely affects skew.

  The present invention has been made in view of the above-described situation, and has a configuration in which differential signal transmission is performed using an even number of four or more coaxial wires, and differential transmission with reduced skew fluctuation in the longitudinal direction of the cable. An object of the present invention is to provide a multicore cable for use.

The multi-core cable for differential transmission according to the present invention is a multi-core cable for differential transmission having an even number of four or more coaxial wires, and the cross-sectional area of the conductor of the coaxial wires is 0.40 mm ^{2 to} 0.00. The pair of coaxial cables that perform differential signal transmission at 004 mm ² are the same in material and dimensions, and the twist pitch of the coaxial cables is a coaxial cable assembled in the multicore cable for differential transmission The pair of coaxial cables that perform differential signal transmission is at least 15 times the outer diameter of the set of the coaxial cables, and the center of the four or more even number of coaxial cables in the cross section perpendicular to the length direction of the coaxial cable. Is a multi-core cable for differential transmission, which is set to be a polygonal diagonal position formed by connecting adjacent ones with a straight line.

  According to the present invention, it is possible to provide a multicore cable for differential transmission that has a configuration in which differential signal transmission is performed using an even number of four or more coaxial wires, and skew fluctuation in the cable longitudinal direction is reduced. it can.

It is a figure which shows the cross-sectional structure of the multi-core signal cable of embodiment which concerns on this invention. It is sectional drawing which shows the structure of each coaxial wire which comprises the multi-core signal cable of FIG. 1A. It is sectional drawing which shows the other structure of the multi-core cable for differential transmission of embodiment which concerns on this invention. It is sectional drawing which shows the further another structure of the multi-core cable for differential transmission of embodiment which concerns on this invention. It is a figure which shows the state which the multi-core signal cable was crushed in the ellipse shape. It is a figure which shows the measurement result of the skew when changing the twist pitch of a coaxial wire.

First, embodiments of the present invention will be listed and described.
(1) The invention related to the multicore cable for differential transmission of the present application is a multicore cable for differential transmission having an even number of four or more coaxial cables, and the cross-sectional area of the conductor of the coaxial cable is 0. in 40mm ² ~0.004mm ^2, a pair of the coaxial cable to perform differential signal transmission, the material and dimensions are the same to each other, twisting pitch of the coaxial cable is by the differential transmission multicore the cable The pair of coaxial cables that perform differential signal transmission is at least 15 times the aggregate outer diameter of the aggregated coaxial cables, and the four or more even numbers in the cross section perpendicular to the length direction of the multicore cable. This is a multi-core cable for differential transmission, which is set to be a polygonal diagonal position formed by connecting the adjacent coaxial cables with a straight line between adjacent ones. As a result, a differential transmission multicore cable with reduced skew variation in the longitudinal direction of the cable can be obtained with a configuration in which differential signal transmission is performed using an even number of four or more coaxial wires. In addition, even when arranged in an elliptical shape instead of being arranged in a coaxial cable circle, the difference in wire length between a pair of coaxial cables that become differential signal lines is reduced, reducing skew fluctuations. Is done.

  (2) When there are a plurality of the coaxial cables, the diagonal lines are polygonal diagonal lines when the centers of the six or more coaxial cables are connected by a straight line, and the same number on both sides of the diagonal lines. It is preferable that it is a diagonal line in which the coaxial electric wire exists. As a result, even if there are six or more even number of coaxial cables, the difference in wire length between the pair of coaxial cables serving as differential signal lines is reduced, and fluctuations in skew are reduced.

  (3) It is preferable to have an interposition between the assembled coaxial cables. Thereby, the shape of the multi-core cable for differential transmission can be stabilized and formed.

  (4) It is preferable to have a shield layer that collectively shields the assembled coaxial wires. Thereby, the shielding effect of the multicore cable for differential transmission can be further improved.

Embodiments of the present invention will be described with reference to the drawings. 1A is a diagram illustrating a cross-sectional configuration of a multicore cable for differential transmission according to an embodiment of the present invention, and FIG. 1B illustrates a configuration of each coaxial cable that configures the multicore cable for differential transmission of FIG. 1A. It is sectional drawing.
In the multicore cable 1 for differential transmission according to this embodiment, four coaxial electric wires 20a, 20b, 20c, and 20d are arranged adjacent to each other. In each of the coaxial wires 20a to 20d, the center conductor 21 is covered with an insulator 22, an outer conductor 23 is provided on the outer periphery of the insulator 22, and the outer side of the outer conductor 23 is covered with an outer sheath 24 to be protected. The coaxial cable, the cross-sectional area of the center conductor 21 is assumed to use one of 0.40mm ² ~0.004mm ^2. In terms of AWG (American Wire Gauge), AWG22 to AWG40 can be used.

  As the central conductor 21 of the coaxial electric wires 20a to 20d, a metal wire made of an annealed copper wire or a copper alloy wire is used. The metal wire may be a stranded wire in which a plurality of wires are twisted or a single wire consisting of only one wire. The metal wire may be plated (tin plating or silver plating). For the insulator 22, for example, a fluororesin or polyethylene resin such as polytetrafluoroethylene (PTFE) or FEP (tetrafluoroethylene-hexafluoropropylene copolymer) is used, and the fluororesin or polyethylene resin is extruded. Is formed by coating. The outer conductor 23 is formed by winding a thin metal wire (which may be plated) such as an annealed copper wire or a copper alloy wire around the outer periphery of the insulator 22 by braiding or horizontal winding. The jacket 24 is formed by extruding a fluororesin, a polyolefin resin, or polyvinyl chloride, or is formed by winding a resin tape such as a polyester tape.

  The periphery of the four coaxial electric wires 20a to 20d is covered with the first outer shield 30, and the outer side thereof is further covered with the second outer shield 40, and the outer cover 50 is further covered as the outermost layer on the outer side. . For example, a metal resin tape or a conductive resin tape is used for the first outer shield 30. The second outer shield 40 is, for example, a braided shield woven with fine metal wires, or a horizontally wound shield in which these fine wires are spirally wound on the first outer shield 30. The first outer shield 30 and the second outer shield 40 correspond to a shield layer that collectively shields a plurality of assembled coaxial cables 20a to 20d.

  FIG. 2 is a cross-sectional view showing another configuration of the multi-core cable for differential transmission according to the embodiment of the present invention. The multi-core cable 1 for differential transmission in FIG. 2 has four coaxial electric wires 20a, 20b, 20c, and 20d as in the configuration in FIG. 1, but is at the center position of these coaxial electric wires 20a to 20d. Thus, the interposition 60 is provided in the gap between the coaxial cables 20a to 20d so that the shape of the multicore cable for differential transmission can be stabilized and molded. For the interposition 60, for example, a resin such as polyethylene polypropylene or a fluororesin having good high-frequency characteristics such as PTFE (tetrafluoroethylene) or PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) can be used. In addition, other resin tubes, jute, paper, and the like can be applied. In addition, the configuration of the four coaxial wires 20a to 20d, the first outer shield 30, the second outer shield 40, and the jacket 50 is the same as the configuration of FIG. 1A.

  FIG. 3 is a cross-sectional view showing still another configuration of the differential transmission multicore cable according to the embodiment of the present invention. The multi-core cable 1 for differential transmission shown in FIG. 3 has four coaxial wires 20a, 20b, 20c, and 20d as well as the configuration shown in FIG. Then, the interposition 60 is provided not only in the center position of the coaxial electric wires 20a to 29d but also on the outer peripheral side of the assembled coaxial electric wires 20a to 30d, and further four interpositions 60 are provided between the adjacent coaxial electric wires. . These interpositions 60 are twisted together with the coaxial electric wires 20a to 20d. As the interposition 60, the same one as that disposed at the center of the cable in FIG. 2 can be used. In addition, other resin strings, tubes, jute, paper, and the like can be applied. In addition, the configuration of the four coaxial wires 20a to 20d, the first outer shield 30, the second outer shield 40, and the jacket 50 is the same as the configuration of FIG. 1A.

The embodiment according to the present invention can be implemented in any of the configurations shown in FIGS.
In the configuration shown in FIGS. 1 to 3, the four coaxial wires 20a to 20d are used as two pairs of coaxial wires, with two coaxial wires as a pair. The pair of coaxial cables is used as a differential signal line. In differential signal transmission using a pair of coaxial cables, high-frequency signals with a phase difference of 180 ° are simultaneously input to two coaxial cables and transmitted, and differential synthesis is performed on the receiving side to increase output and reduce noise. Is granted. A pair of coaxial electric wires that perform differential signal transmission have the same material and dimensions. For example, each coaxial cable can be cut out from the same coaxial cable, and two coaxial cables having the same cross-sectional shape and the material, length, thickness of each layer and the like can be used in pairs.

As shown in FIG. 1A, the plurality of coaxial cables 20a to 20d are ideally aligned adjacent to each other so that the outer periphery thereof is within a circle. That is, a line connecting the centers of the four coaxial cables 20a to 20d and a line connecting the outermost peripheral positions of the coaxial cables 20a to 20d are arranged on a concentric circle, and the coaxial cables are arranged around the center of the concentric circle in the circumferential direction of the concentric circle. It is preferable that 20a-20d adjoins and is arranged in the circle.
However, as described above, when the differential transmission multi-core cable 1 is manufactured or used, the surroundings of the cross-sections of the assembled coaxial wires 20a to 20d may be deformed into an ellipse instead of a circle.

  Therefore, in the embodiment according to the present invention, the pair of coaxial cables used as the differential signal lines are coaxial cables positioned on a rectangular diagonal line connecting the centers of the four coaxial cables 20a to 20d with straight lines. That is, in the example of FIG. 1A, the coaxial cables 20a and 20c and the coaxial cables 20b and 20d are each used as a pair of differential signal lines to perform differential signal transmission. FIG. 4 is a diagram illustrating a state in which the multicore signal cable is crushed into an ellipse. The four coaxial cables 20a to 20d are not formed in a shape in which the coaxial cables 20a to 20d are arranged in a circle, but are also distorted in an elliptical shape as shown in FIG. The difference in line length between the pair of coaxial cables (the pair P1 of the coaxial cables 20a and 20c and the pair P2 of the coaxial cables 20b and 20d) becomes small.

  Next, the twist pitch of the four coaxial wires 20a to 20d will be described. The four coaxial wires 20a to 20d are assembled when the multi-core cable 1 for differential transmission is manufactured, twisted and covered with the first outer shield 30 and the second outer shield 40 around the outer periphery. 50 is coated by resin extrusion. Further, in the configuration using the interposition 60 for both the coaxial electric wires 20a to 20d, the interposition 60 is unwound and assembled together with the coaxial electric wires 20a to 20d, the coaxial electric wires 20a to 20d and the interposition 60 are twisted together, and the first around the first An outer shield 30, a second outer shield 40, and a jacket 50 are provided.

  At this time, in embodiment which concerns on this invention, the twist pitch of coaxial electric wire 20a-20d shall be 15 times or more of the aggregate diameter of coaxial electric wires 20a-20d. The twist pitch of the coaxial cables 20a to 20d means that the coaxial cables 20a to 20d rotate in the circumferential direction around the central axis of the differential transmission multi-core cable 1 (rotate 360 °) in the central axis direction. Shows the distance traveled along. The aggregate diameter of the coaxial cables 20a to 20d is a circle connecting the outermost circumferences of the coaxial cables 20a to 20d when the four coaxial cables 20a to 20d are assembled to form the multi-core cable 1 for differential transmission. Is the diameter.

  FIG. 5 is a diagram illustrating a measurement result of skew when the twist pitch of the coaxial cable is changed. Skew is shown as the difference in delay time between two coaxial wires used as differential signal lines. Here, a plurality of multi-core cables for differential transmission in which the twist pitch of the coaxial cable is 12 times the aggregate diameter of the coaxial cable, and the twist pitch of the coaxial cable is 15 or 18 times the aggregate diameter of the coaxial cable. The skew of multiple multi-core cables for differential transmission is measured, and the result of integrating the frequency for each measured value (ps / m) is shown. The required skew level here is 8 ps / m or less, but the differential measurement multicore cable with the twisted pitch of the coaxial cable being 15 times or more has a skew measurement result distributed between 0 ps / m and 7 ps / m. However, the skew was smaller than 8 ps / m in all the multicore cables for differential transmission. On the other hand, in the differential transmission multicore cable in which the twisting pitch of the coaxial cable is 12 times, the skew measurement results are distributed in the range of 4 ps / m to 12 ps / m, and many measurement results greater than 8 ps / m are obtained. It was.

  Thereby, it becomes difficult to express the line length difference of the coaxial cable used as a differential signal line by making the twist pitch of the coaxial cables 20a to 20d 15 times or more of the aggregate diameter of the coaxial cables 20a to 20d. A multi-core cable 1 for differential transmission having skew characteristics can be obtained. Thereby, the multi-core cable 1 for differential transmission according to the required skew level can be efficiently produced without reducing the process capability index (Cpk). The twist pitch of the coaxial wires 20a to 20d is preferably 30 times or less the aggregate diameter of the coaxial wires 20a to 20d.

In the multi-core cable for differential transmission according to the embodiment of the present invention, the number of coaxial cables is not limited to four, and can be an even number of four or more coaxial cables. In this case as well, a pair of coaxial cables that perform differential signal transmission use the same material and dimensions, and are positioned on a polygonal diagonal line that connects the centers of multiple coaxial cables with straight lines. Coaxial cable to be used.
In this case, in an even number of six or more coaxial cables, there are a plurality of polygonal diagonal lines connecting the centers of the coaxial cables with a straight line, and one of the coaxial cables has a plurality of diagonal lines. The same number of other coaxial wires are arranged, and a pair of coaxial wires located on the diagonal are preferably used as coaxial wires for differential signal transmission. At this time, the twist pitch of the coaxial cable is preferably 15 times or more the aggregate diameter of the coaxial cable. Thereby, the multicore cable for differential transmission which has a favorable skew characteristic can be obtained.

DESCRIPTION OF SYMBOLS 1 ... Multi-core cable for differential transmission, 20a ... Coaxial electric wire, 20b ... Coaxial electric wire, 20c ... Coaxial electric wire, 20d ... Coaxial electric wire, 21 ... Center conductor, 22 ... Insulator, 23 ... Outer conductor, 24 ... Outer sheath, 30 ... first outer shield, 40 ... second outer shield, 50 ... outer jacket, 60 ... intervening.

Claims (4)

A multi-core cable for differential transmission having four or more even number of coaxial wires,
Sectional area of the conductor of the coaxial cable is a 0.40mm ² ~0.004mm ^2, a pair of the coaxial cable to perform differential signal transmission, the material and dimensions are the same to each other,
The twist pitch of the coaxial cable is 15 times or more of the aggregate outer diameter of the coaxial cable assembled in the multi-core cable for differential transmission,
The pair of coaxial cables that perform the differential signal transmission can be formed by connecting the centers of the four or more coaxial cables adjacent to each other in a straight line in a cross section perpendicular to the length direction of the multicore cable. A multi-core cable for differential transmission that is set to have a diagonal diagonal position.   When there are six or more coaxial wires, the diagonal line is a polygonal diagonal line obtained by connecting the centers of the six or more coaxial wires with a straight line, and the same number of coaxial wires on both sides of the diagonal line. The multi-core cable for differential transmission according to claim 1, which is a diagonal line in which there exists.   The multicore cable for differential transmission according to claim 1, wherein the multicore cable for differential transmission has interposition between the assembled coaxial electric wires. The multicore cable for differential transmission according to any one of claims 1 to 3, further comprising a shield layer that collectively shields the assembled coaxial electric wires.

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