JP2017139189A - Differential signal transmission cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a differential transmission cable capable of suppressing a transmission noise from increasing.SOLUTION: Differential signal wires 20A and 20B including a pair of core wires 21 for transmitting a differential signal, an insulator 22 formed of a material having an insulating property covering the core wire 21, a shield tape 23 that has an insulating layer formed from a material having an insulating property and a conductive layer formed of a material having conductivity, and is arranged by winding in spiral a circumference of the insulating body with the conductive layer arranged on the outside, and an insulating tape 26 arranged by winding a circumference of the shield tape 23 are provided as a bundle, and sack out frequencies where attenuation of an electric signal transmitted in the differential signal lines 20A and 20B increases are different from each other.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a differential signal transmission cable.

  In high-speed electrical signal transmission between electronic devices, signals are transmitted using differential signals. In such a differential signal transmission cable for transmitting an electric signal, two cores and an insulator covering the core are aligned in the longitudinal direction or arranged in parallel. A shield tape in which a metal conductor is bonded to an insulating tape is wound around the differential signal line.

  An insulating tape is further wound around the outside of the shield tape. A differential signal transmission cable is formed by combining a plurality of (for example, two) differential signal lines each consisting of a two-core core wire and an insulator, and having a shield and insulation coating around the two. (For example, see Patent Documents 1 to 3.) As a method of winding the above-described shield tape, a method is known in which the shield tape is wound in a spiral shape, and a press-winding insulating tape is wound around the wound shield tape.

JP 2009-2111855 A Japanese Patent Laid-Open No. 7-288047 JP 2012-169269 A

  In the differential signal transmission cables described in Patent Documents 1 to 3 described above, the winding pitches of the shield tapes on the individual differential signal lines are all the same. For this reason, the suck-out frequencies of the differential signal lines generated due to the spiral structure of the shield tape are all the same. The suckout frequency is a frequency at which attenuation of an electric signal transmitted through the differential signal line increases.

  Large electromagnetic noise having a frequency close to the suckout frequency is radiated from the periphery of the winding of the shield tape. Since electromagnetic noise emission and reception are symmetrical characteristics, differential crosstalk is greatly deteriorated when differential signal lines having the same winding pitch of the shield tape are arranged at close positions.

  In other words, an electric signal having a frequency close to the sackout frequency is easily transmitted and received between two differential signal lines arranged at close positions, and an electric signal transmitted through one differential signal line is transmitted to the other. It becomes easy to mix in the differential signal line. That is, there is a problem that transmission noise increases in a differential signal transmission cable having a plurality of differential signal lines due to deterioration of crosstalk.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a differential signal transmission cable that can suppress an increase in transmission noise.

In order to achieve the above object, the present invention provides the following means.
The differential signal transmission cable of the present invention is formed of a pair of core wires that transmit a differential signal, an insulator formed of an insulating material that covers the core wires, and an insulating material. A shield tape having an insulating layer and a conductive layer formed of a conductive material, and arranged by being spirally wound around the insulator, and the shield tape formed of a material having an insulating property And a plurality of differential signal lines provided with an insulating tape that is wound around the periphery of each of the plurality of differential signal lines, and the plurality of differential signal lines attenuates electrical signals transmitted through the differential signal lines Are different from each other.

  According to the differential signal transmission cable of the present invention, since a plurality of differential signal lines having different suckout frequencies are provided as a bundle, the deterioration of crosstalk between the plurality of differential signal lines is suppressed. Can do.

  According to the differential signal transmission cable of the present invention, an increase in transmission noise can be suppressed by providing a plurality of differential signal lines having different suckout frequencies as a bundle.

It is sectional drawing explaining the structure of the cable for differential signal transmission which concerns on one Embodiment of this invention. It is a perspective view explaining the structure of the differential signal line | wire of FIG. It is a perspective view explaining the pitch of the shield tape in two differential signal lines. It is a figure explaining the relationship between the suckout frequency in a differential signal line, and the pitch of a shield tape. It is a graph explaining the signal transmission characteristic, noise radiation reception characteristic, and crosstalk in two differential signal lines.

A differential signal transmission cable according to an embodiment of the present invention will be described with reference to FIGS.
The differential signal transmission cable 10 described in the present embodiment is used for communication of signal information in, for example, a supercomputer or a server installed in a data center, and a supercomputer, a server, and the like are arranged. It is used for communication in a relatively short distance such as in a rack. An example of the communication speed by the differential signal transmission cable 10 is 25 Gbit / s.

  As shown in FIG. 1, the differential signal transmission cable 10 is mainly provided with two differential signal lines 20, a braided shield 30, and a sheath 40. As shown in FIGS. 1 and 2, the differential signal line 20 includes a pair of core wires 21, an insulator 22, a shield tape 23, a first layer pressing winding insulating tape 24, and a second layer pressing winding. A press-winding insulating tape (insulating tape) 26 having an insulating tape 25 is mainly provided.

  One of the pair of core wires 21 is a conductor that transmits a plus signal as a differential signal, and the other is a conductor that transmits a minus signal as a differential signal. In the present embodiment, the core wire 21 will be described as being applied to the one having a diameter defined by 34 AWG (American Wire Gauge: US Wire Gauge Standard: 34 wire (34 gauge)). A signal line conductor having a diameter larger than the diameter to be used may be used, or a core wire 21 having a small diameter may be used, and the diameter is not limited.

  The insulator 22 covers the pair of core wires 21 and has a cross-sectional shape formed of a pair of parallel lines having the same length and a pair of semicircular shapes. A pair of core wires 21 are arranged inside the insulator 22 so as to be arranged at a predetermined interval, and the insulator 22 has a thickness of at least a predetermined thickness around the core wire 21. .

  Note that the cross-sectional shape of the insulator 22 may be a shape composed of a pair of parallel lines having the same length and a pair of semicircular shapes as described above, or may be a substantially elliptical shape. However, it may be a substantially circular shape in which the pair of core wires 21 are individually covered, and is not particularly limited.

  Examples of the material constituting the insulator 22 include foamed polyethylene (Foamed Poly-Ethylene) in order to give the differential signal transmission cable 30 flexibility. Note that the material constituting the insulator 22 may be foamed polyethylene as described above, or may be another material that satisfies the conditions such as insulation required for the insulator 22. It is not intended to limit.

  The shield tape 23 is provided around the insulator 22 so as to cover most of the insulator 22 excluding the end portion along the longitudinal direction, and suppresses the influence of external noise. The shield tape 23 is formed by laminating an insulating layer formed of a resin such as polyester and a conductive layer that is a metal foil layer formed of a conductive metal material such as copper.

  The shield tape 23 is disposed such that the insulating layer is on the inner side (in other words, the insulator 22 side) and the conductive layer is on the outer side. The shield tape 23 is a sheet formed in a rectangular shape, and is arranged by winding the insulator 22 in a spiral shape. In the present embodiment, the shield tape 23 is described as applied to an example in which the insulating layer is disposed inside and the conductive layer is disposed outside. However, the insulating layer is disposed outside and the conductive layer is disposed inside. It may be arranged.

  In the present embodiment, as shown in FIG. 3, the first pitch Pa, which is an interval at which the shield tape 23 in one differential signal line 20A of the two differential signal lines 20 and 20 is spirally wound. The second pitch Pb, which is the interval at which the shield tape 23 in the other differential signal line 20B is spirally wound, is made narrower (narrower pitch).

  More specifically, the first pitch Pa and the second pitch Pb are set such that the respective shield winding pitches (or intervals of spiral winding) differ by 20% or more. In other words, the expression (second pitch Pb) <(first pitch Pa × 0.8) is satisfied. In other words, the first pitch Pa and the second pitch Pb are set such that the difference in suckout frequency in the differential signal line 20 is at least 3 GHz.

  Here, the relationship between the suck-out frequency in the differential signal line 20 and the pitch of the shield tape 23 will be described with reference to FIG. When the suckout frequency is 19 GHz, the pitch is 4.9 mm, and when the suckout frequency is 21 GHz, the pitch is 4.3 mm. Further, when the sackout frequency is 24 GHz, the pitch is 3.4 mm, and when the sackout frequency is 30 GHz, the pitch is 2.4 mm.

  As described above, the combination satisfying the expression (second pitch Pb) <(first pitch Pa × 0.8) is a combination of the pitches of 2.4 mm and 3.4 mm, 2.4 mm and 4.3 mm. Combination, 2.4 mm and 4.9 mm. Furthermore, a combination of 3.4 mm and 4.3 mm and a combination of 3.4 mm and 4.9 mm are also mentioned. In the case of these combinations, the difference in suckout frequency in the differential signal line 20 is at least 3 GHz.

  Note that the pitch value and the sac-out frequency value of the shield tape 23 shown in FIG. 4 are examples, and the pitch value and the sac-out frequency value in the present invention are not limited to these values. Absent.

  In the present embodiment, when a characteristic characteristic of one of the two differential signal lines 20 and 20 is described, the differential signal line 20A and the differential signal line 20B are described. When the features common to the two are described, they are simply expressed as differential signal lines 20.

  As shown in FIG. 2, the first layer pressing and winding insulating tape 24 and the second layer pressing and winding insulating tape 25 (the pressing and winding insulating tape 26) are arranged around the shield tape 23, and are connected to the differential signal line 20. Is to protect. The first layer press-winding insulating tape 24 and the second layer press-winding insulating tape 25 are members formed in a rectangular tape shape formed of polyester, and the shield tape 23 is wound around in a spiral shape. It is something to cover.

  In this embodiment, the first layer press-winding insulating tape 24 and the second layer press-winding insulating tape 25 are described as being applied to an example in which the resin is polyester. Other materials may be used as long as the resin satisfies the conditions such as insulation and durability required for the tape 24 and the second layer pressing and winding insulating tape 25, and there is no particular limitation.

  The first layer pressing and winding insulating tape 24 is spirally wound on the shield tape 23, and the second layer pressing and winding insulating tape 25 is the first layer pressing and winding insulating tape. 24 is arranged in a spiral form on 24. In the present embodiment, the differential signal line is wound in the longitudinal direction as compared with the angle between the longitudinal direction of the differential signal line and the edge of the first layer pressing and winding insulating tape 24 to be wound. Description will be made by applying to an example where the angle between the second layer pressing and winding insulating tape 25 is small.

  As shown in FIG. 1, the braided shield 30 covers the periphery of the two differential signal lines 20 and 20 and is formed in a cylindrical shape by incorporating a plurality of ancestors. The sheath 40 covers the periphery of the braided shield 30 and forms the outer shape of the differential signal transmission cable 10.

  Next, transmission of differential signals in the differential signal transmission cable 10 having the above-described configuration will be described with reference to FIG. FIG. 5 is a graph illustrating signal transmission characteristics and noise radiation reception characteristics in the differential signal line 20A and the differential signal line 20B, and crosstalk between the differential signal line 20A and the differential signal line 20B. In FIG. 5, the horizontal axis represents the frequency of the electric signal, and the vertical axis represents the transmission characteristic, the radiation characteristic, and the crosstalk.

  The signal transmission characteristic and the noise radiation reception characteristic in the differential signal line 20A are respectively shown by a graph A1 and a graph A2 indicated by a solid line. As can be seen from the graphs A1 and A2, the signal transmission characteristics are reduced and the noise radiation reception characteristics are increased at the suck-out frequency SA.

  Further, the signal transmission characteristic and the noise radiation reception characteristic in the differential signal line 20B are respectively shown by a graph B1 and a graph B2 represented by dotted lines. As can be seen from the graph B1 and the graph B2, at the sac-out frequency SB that is higher than the sac-out frequency SA, the signal transmission characteristics are reduced and the noise radiation reception characteristics are increased. This is considered to be because the pitch Pb of the shield tape 23 in the other differential signal line 20B is narrower than the pitch Pa of the shield tape 23 in the differential signal line 20A.

  Further, the crosstalk between the differential signal line 20A and the differential signal line 20B is indicated by a graph CT represented by a one-dot chain line. As can be seen from the graphs A2, B2 and CT, the peak frequency (suckout frequency SA) of the noise radiation reception characteristic in the differential signal line 20A and the peak frequency (sackout) of the noise radiation reception characteristic in the differential signal line 20B. Since the frequency SB) is different, an increase in the peak value of the graph CT showing the crosstalk is suppressed as compared with the case where the peak frequencies match.

According to the differential signal transmission cable 10 having the above-described configuration, the differential signal line 20A and the differential signal line 20B having different suckout frequencies are provided as a bundle. Deterioration of crosstalk during 20B can be suppressed. As a result, an increase in transmission noise in the differential signal transmission cable 10 can be suppressed. Specifically, by making the pitch of the shield tape 23 in the differential signal line 20A and the differential signal line 20B different from each other, The suckout frequencies are also different from each other. The suckout frequency is also determined by the periodicity of the spiral structure of the shield tape 23 wound in a spiral. Therefore, the suck-out frequencies in the differential signal line 20A and the differential signal line 20B are different from each other in the frequency SA and the frequency SB, and the deterioration of the crosstalk between the differential signal line 20A and the differential signal line 20B can be suppressed. it can.

  Further, the relationship of the pitch of the shield tape 23 in the differential signal line 20A and the differential signal line 20B is a relationship satisfying the expression of (second pitch Pb) <(first pitch Pa × 0.8), and the sac-out By setting the frequency difference to be at least 3 GHz, it becomes easy to suppress the deterioration of the crosstalk between the differential signal line 20A and the differential signal line 20B.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the description is made by applying to the example in which the differential signal lines 20 are two, but three or more differential signal lines 20 may be provided, and in particular, the number It is not intended to limit.

  DESCRIPTION OF SYMBOLS 10 ... Cable for differential signal transmission, 20, 20A, 20B ... Differential signal line, 21 ... Core wire, 22 ... Insulator, 23 ... Shield tape, 26 ... Insulation tape for press winding (insulation tape), Pa ... No. 1 pitch, Pb ... 2nd pitch

Claims (4)

A pair of cores for transmitting differential signals;
An insulator formed of an insulating material covering the core wire;
A shielding tape having an insulating layer formed from a material having an insulating property and a conductive layer formed from a material having a conductive property and arranged around the insulator in a spiral shape; and
A plurality of differential signal lines provided with a plurality of differential signal lines provided with an insulating tape formed of a material having insulating properties and wound around the shield tape,
The plurality of differential signal lines are differential signal transmission cables having different suckout frequencies at which attenuation of electrical signals transmitted through the differential signal lines is increased.   The differential signal transmission cable according to claim 1, wherein a plurality of the differential signal lines have different pitches, which are intervals at which the shield tape is spirally wound. The shield tape in a part of the differential signal lines among the plurality of differential signal lines is spirally wound at a first pitch, and the shield tape in the other part of the differential signal lines. Is spirally wound at the second pitch,
The operating signal transmission cable according to claim 2, wherein the first pitch and the second pitch satisfy a relationship of (second pitch) <(first pitch × 0.8).   A frequency of at least 3 GHz between the sac out frequency in a part of the differential signal lines of the plurality of the differential signal lines and the sack out frequency in the other part of the differential signal lines. The operation signal transmission cable according to claim 1, wherein there is a difference.

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