JP2016076368A - Cable for differential signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cable for a differential signal capable of reducing a propagation time difference between an in-phase component and a differential component.SOLUTION: A cable 1 for a differential signal comprises a pair of conductors 2 arranged in parallel to each other, inner skin layers 3 consisting of a non-foamed insulator and formed individually so as to cover the respective outer peripheries of the conductors 2, a foam layer 4 consisting of a foamed insulator and formed so as to collectively cover the outer peripheries of both inner skin layers 3, and an outer skin layer 5 consisting of a non-foamed insulator and formed so as to cover the outer periphery of the foam layer 4. The outer skin layer 5 has an uneven thickness. The inner skin layers 3 and the outer skin layer 5 are formed from non-foamed insulators having the same dielectric constant. At least the thickness of the inner skin layers 3 located between the pair of conductors 2 and the thickness of the outer skin layer 5 at a position overlapping with the conductors 2 in the arrangement direction of the pair of conductors 2 and in the vertical direction are formed equally.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a differential signal cable.

  Conventionally, a pair of conductors arranged in parallel, a foam layer made of a foam insulator formed so as to cover the pair of conductors at once, and a non-foam formed so as to cover the outer periphery of the foam layer A differential signal cable including an outer skin layer made of an insulator is known.

  In addition, there exists patent document 1 as prior art document information relevant to invention of this application.

JP 2011-86458 A

  However, in the above-described conventional differential signal cable, the effective permittivity differs between the in-phase component and the differential component of the signal, the propagation time of the in-phase component and the differential component increases, and electrical characteristics such as skew are increased. There was a problem that it might deteriorate.

  Accordingly, an object of the present invention is to provide a differential signal cable capable of solving the above-described problems and reducing the difference in propagation time between the in-phase component and the differential component.

  The present invention was devised to achieve the above object, and includes a pair of conductors arranged in parallel and a non-foamed insulator formed individually so as to cover the outer periphery of each of the pair of conductors. An inner skin layer, a foam layer made of a foam insulator formed so as to cover the outer periphery of the inner skin layer, and so as to collectively cover the pair of conductors and the inner skin layer, An outer skin layer made of a non-foamed insulator formed so as to cover the outer periphery of the foam layer, the outer skin layer having a non-uniform thickness, and the inner skin layer and the outer skin layer are A non-foamed insulator having the same dielectric constant, and at least a thickness of the inner skin layer located between the pair of conductors and a position overlapping the conductors in a direction perpendicular to the arrangement direction of the pair of conductors Of the outer ski A differential signal cables the thickness of the layers are formed equally.

  The outer skin layer may be formed such that a portion overlapping the conductor in a direction perpendicular to the arrangement direction of the pair of conductors and a thickness sandwiched between the portions overlapping the conductor are equal.

  The thickness of the foam layer sandwiched between the pair of conductors may be equal to the thickness of the foam layer sandwiched between the conductor and the outer skin layer.

  The inner skin layer may be formed to have a uniform thickness over the entire circumference.

  The foamed layer has an oval shape including two straight portions parallel to the arrangement direction of the pair of conductors and a semicircular arc portion connecting ends of the straight portions in a cross-sectional view. The outer skin layer formed on the outer periphery of the arc portion may be thicker than the outer skin layer formed on the straight portion.

  ADVANTAGE OF THE INVENTION According to this invention, the cable for differential signals which can make small the propagation time difference of an in-phase component and a differential component can be provided.

It is a cross-sectional view of a differential signal cable according to an embodiment of the present invention. (A) is an example of intensity distribution of a differential electric field, (b) is a figure which shows an example of intensity distribution of an in-phase electric field.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view of a differential signal cable according to the present embodiment.

  As shown in FIG. 1, a differential signal cable 1 is composed of a pair of conductors 2 arranged in parallel and a non-foamed insulator formed individually so as to cover the outer periphery of each of the pair of conductors 2. The inner skin layer 3 is provided so as to cover the outer periphery of the inner skin layer 3, and the pair of conductors 2 and the inner skin layer 3 (conductor 2 provided with two inner skin layers 3) are collectively covered. A foamed layer 4 made of a foamed insulator, and an outer skin layer 5 made of a non-foamed insulator formed so as to cover the outer periphery of the foamed layer 4.

  As the conductor 2, an annealed copper wire, a silver plating annealed copper wire, etc. can be used, for example. Although not shown, a shield layer may be formed by winding a metal tape made of aluminum, copper, silver or the like around the outer periphery of the outer skin layer 5.

  In the present embodiment, the foam layer 4 includes two straight portions 4a parallel to the arrangement direction of the pair of conductors 2 in a cross-sectional view, and a semicircular arc portion 4b that connects the ends of the straight portions 4a. Are formed into an oval shape. For example, the foam layer 4 may be formed in an elliptical shape in a cross-sectional view.

  In the differential signal cable 1, an electric field generated by the in-phase component of the signal (hereinafter referred to as an in-phase electric field) and an electric field generated by the differential component of the signal (hereinafter referred to as a differential electric field) The intensity distribution is very different.

  Specifically, as shown in FIG. 2A, the differential electric field becomes the largest (the strongest electric lines of force pass) between the conductors 2 (indicated by arrows in FIG. 2A). It can be said that the permittivity distribution between the conductors 2 greatly contributes to the effective permittivity and propagation time of the differential component.

  On the other hand, as shown in FIG. 2B, the in-phase electric field is the largest (the strongest electric lines of force pass) are the upper and lower portions of the conductor 2 (portions indicated by arrows in FIG. 2B). It can be said that the permittivity distribution of the upper and lower portions of the conductor 2 greatly contributes to the effective permittivity and propagation time of the in-phase component.

  In the conventional differential signal cable having no inner skin layer 3, the insulator between the conductors 2 where the differential electric field is the largest is only the foam layer 4, whereas the common-mode electric field is the largest. Since the insulators in the upper and lower portions of the conductor 2 include both the foam layer 4 and the outer skin layer 5, due to the influence of the outer skin layer 5, the difference in effective dielectric constant between the in-phase component and the differential component is large. Therefore, the propagation time difference between the in-phase component and the differential component (hereinafter referred to as differential in-phase propagation time difference) has become large.

  Therefore, the present inventors attempted to suppress the differential common-mode propagation time difference by using the same insulator configuration for the portion where the differential electric field is greatest and the portion where the common-mode electric field is greatest.

  That is, in the differential signal cable 1 according to the present embodiment, the inner skin layer 3 and the outer skin layer 5 are made of a non-foamed insulator having the same dielectric constant, and are positioned at least between the pair of conductors 2. The thickness of the inner skin layer 3 (parts indicated by A1 and A2 in FIG. 1) and the outer skin layer 5 (indicated by B1 to B4 in FIG. 1) at positions overlapping the conductors 2 in the direction perpendicular to the arrangement direction of the pair of conductors 2 The thickness of the part) is all equal.

  Further, in the differential signal cable 1, the thickness d1 of the foam layer 4 sandwiched between the conductors 2 and the thickness d2 of the foam layer 4 sandwiched between the conductors 2 and the outer skin layer 5 are all It is formed to be equal. Since the foam layer 4 has a low dielectric constant and some errors are allowed, some differences in the thicknesses d1 and d2 are allowed. In order to make the dielectric constant of the foam layer 4 uniform, the foam layer 4 is preferably formed so that the degree of foaming is as uniform as possible.

  With this configuration, in both the differential electric field and the in-phase electric field, an insulator having the same dielectric constant and the same thickness (a non-foamed insulator, a foamed insulator, and a non-foamed material) is provided in a path where the electric field strength is maximum. Therefore, the differential common-mode propagation time difference can be made close to zero.

  Here, since the dielectric constant distribution in the vicinity of the conductor 2 has a great influence on electrical characteristics such as skew, it is desirable that the inner skin layers 3 be formed to have a uniform thickness over the entire circumference.

  As for the outer skin layer 5, as shown in FIGS. 2A and 2B, in the vicinity of the end in the arrangement direction of the conductors 2 (the left and right end portions in the drawing), the electric field strength is weak for both in-phase and differential. Therefore, it can be said that the thickness of this portion has little influence on the electrical characteristics. Therefore, the outer skin layer 5 may have a non-uniform thickness.

  In manufacturing, it is difficult to form the entire outer skin layer 5 with a strictly uniform thickness, but according to this embodiment, the portions indicated by B1 to B4 in FIG. If they are formed to have the same thickness, it is possible to suppress deterioration of electrical characteristics. That is, according to this embodiment, it can be said that the differential signal cable 1 that is easy to manufacture and has good electrical characteristics can be realized. In the present embodiment, the thickness of the outer skin layer 5 formed on the outer periphery of the arc portion 4 b of the foam layer 4 is formed to be thicker than the thickness of the outer skin layer 5 formed on the straight portion 4 a of the foam layer 4. Yes.

  As shown in FIG. 2B, the in-phase electric field is relatively large even in the central portion in the arrangement direction of the conductors 2, and more preferably, the electric field between the conductors 2 in the direction perpendicular to the arrangement direction of the pair of conductors 2. In addition to the overlapping portions (portions indicated by B1 to B4 in FIG. 1), the thicknesses of the portions (portions indicated by C1 and C2 in FIG. 1) sandwiched between the overlapping portions of the conductor 2 are also the same thickness as the inner skin layer 3 It is desirable to form it.

  As the non-foamed insulator used for the inner skin layer 3 and the outer skin layer 5, for example, PE (polyethylene) may be used. In the present embodiment, PE is used for the inner skin layer 3 and the outer skin layer 5, and foamed PE is used for the foam layer 4. In addition, resin used for the inner skin layer 3, the foam layer 4, and the outer skin layer 5 is not limited to this, For example, FEP may be used. Further, the foaming method of the foamed resin used for the foam layer 4 may be either physical foaming or chemical foaming.

  As described above, in the differential signal cable 1 according to the present embodiment, the outer skin layer 5 has a non-uniform thickness, and the inner skin layer 3 and the outer skin layer 5 have the same dielectric constant. The outer skin layer 5 is formed of a foamed insulator and has at least a thickness of the inner skin layer 3 positioned between the pair of conductors 2 and a position overlapping the conductors 2 in a direction perpendicular to the arrangement direction of the pair of conductors 2. The thickness is equal.

  As a result, the difference in effective dielectric constant between the in-phase component and the differential component of the signal can be reduced, and the differential in-phase propagation time difference can be minimized. As a result, it is possible to suppress deterioration of electrical characteristics such as skew.

  In addition, according to the present embodiment, an effect that the effective dielectric constant around the conductor 2 can be made uniform is obtained, so that the symmetry of the electric field can be maintained and the Scd 21 can be improved.

  Furthermore, according to the present embodiment, the designed differential common-mode propagation time difference can be brought close to 0, so that it is possible to exclude this factor when considering the cause when the electrical characteristics deteriorate. , It will be easier to deepen the discussion.

  The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.

1 Cable for differential signal 2 Conductor 3 Inner skin layer 4 Foam layer 5 Outer skin layer

Claims (5)

A pair of conductors arranged in parallel;
An inner skin layer made of a non-foamed insulator formed individually so as to cover the outer periphery of each of the pair of conductors;
A foam layer made of a foam insulator formed so as to cover the outer periphery of the inner skin layer, and to cover the pair of conductors and the inner skin layer together,
An outer skin layer made of a non-foamed insulator formed so as to cover the outer periphery of the foam layer, and
The outer skin layer has a non-uniform thickness.
The inner skin layer and the outer skin layer are composed of a non-foamed insulator having the same dielectric constant,
At least the thickness of the inner skin layer positioned between the pair of conductors is equal to the thickness of the outer skin layer at a position overlapping the conductors in the direction perpendicular to the arrangement direction of the pair of conductors. The cable for differential signals characterized by this. The differential according to claim 1, wherein the outer skin layer is formed such that a portion overlapping the conductor in a direction perpendicular to the arrangement direction of the pair of conductors and a portion sandwiched between the portions overlapping the conductor are equal in thickness. Signal cable. The difference according to claim 1 or 2, wherein the thickness of the foam layer sandwiched between the pair of conductors is equal to the thickness of the foam layer sandwiched between the conductor and the outer skin layer. Motion signal cable. The differential signal cable according to claim 1, wherein the inner skin layer is formed to have a uniform thickness over the entire circumference. The foamed layer has an oval shape including two straight portions parallel to the arrangement direction of the pair of conductors and a semicircular arc portion connecting ends of the straight portions in a cross-sectional view. Formed,
The differential signal cable according to claim 1, wherein a thickness of the outer skin layer formed on an outer periphery of the arc portion is thicker than a thickness of the outer skin layer formed on the linear portion.

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