JP2018196004A - High frequency transmission line - Google Patents

Abstract

To adjust characteristic impedance at a bent portion without changing a line width of a signal line at a bent portion.SOLUTION: A signal line 12 is formed with a bent portion 12Z at which two straight line portions 12X and 12Y each having an extending direction different from each other connected to each other. Immediately below the convex side angle P of the bent portion 12Z in a ground plane 13, an opening 14 where a grounding conductor is being selectively removed is provided.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a high-frequency transmission line in which a signal line having a bent portion is formed on the surface of a substrate.

The high-frequency transmission line uses a bent transmission line shape instead of a symmetric linear structure because it is difficult to secure a sufficient wiring area due to recent downsizing of modules and higher mounting density. There are things that must be done.
In the high-frequency transmission line having such a bent portion, the characteristic impedance changes at the bent portion. As a result, the characteristic impedance becomes discontinuous between the straight portion and the bent portion, and the transmission characteristics deteriorate. In some cases, a standing wave having a bent portion as a reflection end is generated to form a stub structure, and only a specific frequency is cut off. In the bent portion, the electric field coupling distribution is asymmetric with respect to the transmission direction of the signal line, so that the characteristic impedance changes.

Conventionally, in such a high-frequency transmission line, as a technique for adjusting the characteristic impedance between the straight portion and the bent portion, the characteristic impedance of the bent portion is adjusted by changing the line width of the signal line in the bent portion. Have been proposed (see, for example, Non-Patent Document 1).
7A and 7B are configuration examples showing a bent portion of a conventional microstrip line, in which FIG. 7A shows a front view and FIG. 7B shows a back view. In this configuration example of the microstrip line, a signal line 52 through which a high-frequency signal flows is formed on the surface of the substrate 51, and a ground plane 53 to which a ground potential is applied to the entire back surface is formed on the back surface of the substrate 51. Has been. A bent portion B where the signal line 52 bends at a right angle is provided in the middle of the signal line 52, and a notch 54 is formed at the convex side corner of the bent portion B.

  FIGS. 8A and 8B are configuration examples showing a bent portion of a conventional coplanar line, in which FIG. 8A shows a front view and FIG. 8B shows a rear view. In this configuration example of the coplanar line, a signal line 62 through which a high-frequency signal flows is formed on the surface of the substrate 61, and surface grounds 65 are formed on both sides thereof. On the back surface of the substrate 61, a ground plane 63 to which a ground potential is applied is formed on the entire back surface. A bent portion B where the signal line 62 bends at a right angle is provided in the middle of the signal line 62, and a notch 64 is formed at the convex side corner of the bent portion B.

  These examples of high-frequency transmission lines are all formed by narrowing the line width of the signal line at the bent part by forming a notch at the convex side of the bent part of the signal line formed on the substrate surface. is there. Thereby, the characteristic impedance of the bent portion can be adjusted.

B.C. Wadell, "Transmission Line Design Handbook", 1991, Artech House Publishers., Pp.289

In general, in a high-frequency transmission line, it is difficult to take a grounding structure that is symmetrical with respect to a signal line at a bent portion. For this reason, in the prior art, by adjusting the line width of the signal line at the bent portion, the characteristic impedance of the bent portion is changed to adjust the characteristic impedance of the straight portion.
However, according to such a configuration of the prior art, since the characteristic impedance of the bent portion is adjusted by narrowing the line width of the signal line, the influence of pattern tolerance at the time of manufacture is large, and the characteristic impedance is the design value. There was a problem that it was easy to deviate greatly. In addition, there is a problem that the current capacity of the signal line is reduced as much as the line width is reduced at the bent portion.

  An object of the present invention is to provide a high-frequency transmission line that can adjust the characteristic impedance of the bent portion without changing the line width of the signal line in the bent portion.

  In order to achieve such an object, a high-frequency transmission line according to the present invention includes a substrate, a signal line formed on the surface of the substrate, and a ground plane made of a ground conductor formed on the back surface of the substrate. The signal line has a bent portion that connects two straight portions with different extending directions, and the ground plane is located immediately below the convex side angle of the bent portion. The ground conductor has an opening selectively removed.

  In addition, one configuration example of the high-frequency transmission line according to the present invention is a region on the convex side corner side of the bent portion of the capacitance component generated between the signal line of the bent portion and the ground plane. The first electric capacity component generated in a certain convex side portion is smaller than the second electric capacity component generated in the concave side portion that is a region on the concave side corner of the bent portion.

  Further, in one configuration example of the high-frequency transmission line according to the present invention, the opening is positioned on a virtual line whose apex passes through the convex side angle and the concave side angle of the bent portion in plan view, and the bottom side Intersects the virtual line and forms an isosceles triangle or isosceles triangle whose apex angle is substantially equal to the bending angle of the bent portion.

  In one configuration example of the high-frequency transmission line according to the present invention, the signal line is a microstrip line or a coplanar line in which a surface ground is formed on the surface of the substrate.

  Further, in one configuration example of the high-frequency transmission line according to the present invention, the signal line is composed of a pair of differential lines in which a normal phase signal line and a negative phase signal line are arranged in parallel to each other, and the opening is Of the positive-phase signal line and the negative-phase signal line, the signal line is formed immediately below the convex side corner of one of the signal lines located on the convex side in the bent portion.

  In one configuration example of the high-frequency transmission line according to the present invention, the substrate is a laminated ceramic substrate in which a plurality of ceramic layers are laminated.

  According to the present invention, it is possible to adjust the characteristic impedance in the convex side portion and the concave side portion of the bent portion without changing the line width of the signal line in the bent portion. For this reason, it is possible to make the characteristic impedance continuous between the straight portion and the bent portion, and as a result, it is possible to suppress deterioration of transmission characteristics.

It is explanatory drawing which shows the structure of the high frequency transmission line concerning 1st Embodiment. It is explanatory drawing which shows the principal part structure of FIG. It is a modification of an opening part. It is explanatory drawing which shows the structure of the high frequency transmission line concerning 2nd Embodiment. It is explanatory drawing which shows the structure of the high frequency transmission line concerning 3rd Embodiment. It is explanatory drawing which shows the structure of the high frequency transmission line concerning 4th Embodiment. It is a structural example which shows the bending part of the conventional microstrip line. It is a structural example which shows the bending part of the conventional coplanar track | line.

Next, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
First, with reference to FIG. 1 and FIG. 2, the high frequency transmission line 10 concerning the 1st Embodiment of this invention is demonstrated. 1A and 1B are explanatory views showing a configuration of a high-frequency transmission line according to the first embodiment, in which FIG. 1A is a surface view and FIG. 1B is a cross-sectional view taken along line AA in FIG. FIG. 1C is a back view. 2 is an explanatory view showing the configuration of the main part of FIG. 1, FIG. 2 (a) is a front view of the main part, FIG. 2 (b) is a cross-sectional view along BB of FIG. 2 (a), and FIG. ) Is an equivalent circuit diagram of a high-frequency transmission line.

  As shown in FIG. 1, the high-frequency transmission line 10 includes a substrate 11, a signal line 12 formed linearly on the surface of the substrate 11, and a ground plane 13 made of a ground conductor formed on the back surface of the substrate 11. I have. The high-frequency transmission line 10 is suitable for an electronic device or an electronic component in which a high-speed electric signal of 10 GHz to 100 GHz or less propagates through a dielectric substrate, for example.

  The substrate 11 is a high frequency substrate in which a conductor layer such as a metal thin film is formed on the upper and lower surfaces (front surface and back surface) of a dielectric layer. For example, the substrate 11 is a laminated ceramic substrate in which a plurality of ceramic layers are laminated. It is configured.

  The signal line 12 is a microstrip line made of a thin film conductor such as metal and having a constant line width W. In the middle of the signal line 12, a bent part 12Z in which the extending direction of the line changes to a predetermined angle is provided, so that two linear parts 12X and 12Y having different extending directions are connected to each other by the bent part 12Z. Has been. In the example of FIG. 1, a straight portion 12X extending in the horizontal direction in plan view and a straight portion 12X extending in the vertical direction in plan view are connected to each other by a bent portion 12Z. Here, a case where the bending angle between the straight portion 12X and the straight portion 12Y in the bent portion 12Z is a right angle (90 °) is shown as an example, but the present invention is not limited to this. The present invention can be similarly applied even when the bending angle is larger or smaller than 90 °.

The ground plane 13 has an opening 14 formed by selectively removing the ground conductor located immediately below the convex side angle (outer edge angle) P of the bent portion 12Z.
The opening 14 has a shape that is symmetric with respect to the virtual line M, and has a base S that is a straight line that is orthogonal to the virtual line M and intersects the bent portion 12Z in plan view. The imaginary line M is a straight line passing through the convex side angle P and the concave side angle (inner edge angle) Q of the bent portion 12Z in plan view.

  In the example of FIG. 1, an example in which the opening 14 is a right-angled isosceles triangle is shown, and the vertex V of the right-angled isosceles triangle is located on the imaginary line M outside the bent portion 12Z from the convex side angle P, The base S of the right-angled isosceles triangle is orthogonal to the imaginary line M and intersects the bent portion 12Z. Thereby, the opening part 14 will be located just under the convex side angle P of the bending part 12Z.

  In the bent portion 12Z of the signal line 12, an electric capacitance component is generated between the signal line 12 on the front surface and the ground plane 13 on the back surface with the dielectric layer of the substrate 11 interposed therebetween. Here, the capacitance component generated in the convex portion 12P, which is the region on the convex side angle P side of the bent portion 12Z, is CP (first capacitance component), and the concave portion Q on the concave side angle Q side of the bent portion 12Z. The capacitance component generated in the concave portion 12Q that is the region is defined as CQ (second capacitance component).

  As a result, the equivalent circuit of the bent portion 12Z is represented by a T-type four-terminal circuit in which a parallel circuit of CP and CQ is sandwiched between two inductances LX and LY, as shown in FIG. The end portion TX is a connection point with the straight portion 12X in the bent portion 12Z, and the inductance LX is an inductance on the straight portion 12X side in the bent portion 12Z. The end TY is a connection point with the straight portion 12Y in the bent portion 12Z, and the inductance LY is an inductance on the straight portion 12Y side in the bent portion 12Z.

  In general, when the opening 14 is not present, as shown in Non-Patent Document 1, the situation is CP> CQ at the bent portion 12Z. Therefore, in the signal line 12, the characteristic impedance differs between the convex portion 12P and the concave portion 12Q of the bent portion 12Z, and the characteristic impedance is not good between the straight portions 12X, 12Y and the bent portion 12Z. It becomes continuous, causing transmission characteristics to deteriorate.

  In the present embodiment, attention is paid to the deviation of the capacitance components CP and CQ in the convex portion 12P and the concave portion 12Q of the bent portion 12Z, and an opening 14 is provided immediately below the bent portion 12Z. . As a result, the distance between the convex side angle P and the ground plane 13 becomes larger than the distance between the concave side angle Q and the ground plane 13, and a condition of CP <CQ is obtained at the bent portion 12Z.

  Therefore, according to the present embodiment, it is possible to adjust the characteristic impedance in the convex portion 12P and the concave portion 12Q of the bent portion 12Z without changing the line width of the signal line 12 in the bent portion 12Z. For this reason, it is possible to make the characteristic impedance continuous between the straight portions 12X and 12Y and the bent portion 12Z, and as a result, it is possible to suppress the deterioration of the transmission characteristics.

  In FIG. 1, the case where the opening 14 is formed of a right-angled isosceles triangle and the length L of two equal sides is larger than the line width W of the signal line 12 is shown as an example. Instead, it is sufficient that the apex angle θ is an isosceles triangle or an approximately isosceles triangle that is substantially equal to the bending angle θZ of the bent portion 12Z. Further, the shape and size of the opening 14 may be arbitrarily designed so that the characteristic impedance is continuous between the straight portions 12X and 12Y and the bent portion 12Z.

  FIG. 3 shows a modification of the opening. FIG. 3A shows a case where the shape of the opening 14 is the right-angled isosceles triangle described above. That is, the opening 14 has a shape that is symmetric with respect to the virtual line M, the vertex V is located on the virtual line M outside the bent portion 12Z from the convex side angle P, and the base S is the virtual line M. And intersect with the bent portion 12Z.

  In general, it is desirable that the apex angle θ of the isosceles triangle is substantially the same as the bending angle θZ of the bent portion 12Z. As a result, the two equilateral sides of the isosceles triangle are in substantially the same extending direction as the straight portions 12X and 12Y, and the equilateral side and the convex side end of the bent portion 12Z are parallel to make the distance between them substantially constant. For this reason, it can suppress that electric capacitance component CP generate | occur | produces partially biasing, and in order to obtain intended CP, the shape and size of the opening part 14 can be designed easily.

  FIG. 3B uses a trapezoid as the shape of the opening 14. This trapezoid is obtained by cutting the vertex V side of the right isosceles triangle shown in FIG. Thereby, substantially the same operation effect as a right isosceles triangle is obtained.

  FIG. 3C shows an isosceles triangle whose apex angle θ is larger than a right angle as the shape of the opening 14. FIG. 3D shows an isosceles triangle whose apex angle θ is smaller than a right angle as the shape of the opening 14. Thereby, even if the bending angle θZ of the bent portion 12Z is other than a right angle, a good effect can be obtained.

  FIG. 3 (e) uses a plano-convex shape as the shape of the opening 14. In this shape, the vertex V side of the isosceles right triangle whose apex angle θ is larger than the right angle shown in FIG. Thereby, substantially the same operation effect as a right isosceles triangle is obtained.

  FIG. 3 (f) uses an unequal triangle as the shape of the opening 14. This shape is non-axisymmetric with respect to the virtual line M, and the vertex V does not necessarily have to be on the virtual line M. According to this shape, the magnitude of the generated capacitance component CP can be adjusted on the straight line portion 12X side and the straight line portion 12Y side. As a result, the reflection characteristics of the high-frequency signals at the straight portions 12X and 12Y can be individually adjusted, the substrates (not shown) connected via the straight portions 12X and 12Y are different, and the reflection characteristics are different. Effective when different.

[Second Embodiment]
Next, with reference to FIG. 4, the high frequency transmission line 10 concerning the 2nd Embodiment of this invention is demonstrated. 4A and 4B are explanatory views showing the configuration of the high-frequency transmission line according to the second embodiment. FIG. 4A is a surface view, and FIG. 4B is a cross-sectional view taken along the line CC in FIG. FIG. 4C is a back view.
This embodiment is different from FIG. 1 in that a notch 12R is provided at the convex side angle P of the bent portion 12Z. However, other configurations such as the opening 14 provided on the back surface of the substrate 11 are described. This is the same as FIG.

That is, in the present embodiment, as shown in FIG. 4, the convex side angle P of the bent portion 12Z has a cutout portion 12R in which a portion of the bent portion 12Z is cut out along the direction orthogonal to the imaginary line M. Is provided.
Thereby, the line | wire width in the bending part 12Z changes, and a characteristic impedance can be adjusted. Therefore, the characteristic impedance can be adjusted by the size and shape of the notch 12R in addition to the opening 14, and the degree of freedom in design can be greatly expanded.

[Third Embodiment]
Next, a high frequency transmission line 10 according to a third embodiment of the present invention will be described with reference to FIG. 5A and 5B are explanatory views showing the configuration of the high-frequency transmission line according to the third embodiment. FIG. 5A is a front view, and FIG. 5B is a cross-sectional view taken along the line DD in FIG. FIG. 5C is a rear view.
The present embodiment is applied to a coplanar line with a back surface ground instead of the microstrip line of FIG. 1, but other configurations such as the opening 14 provided on the back surface of the substrate 11 are shown in FIG. It is the same.

That is, in the present embodiment, as shown in FIG. 4, the signal line 12 formed on the surface of the substrate 11 is constituted by a coplanar line, and the signal line 12 and a gap having a constant width are formed on both sides of the signal line 12. A surface ground 15 is formed across the surface.
Thereby, even if the signal line 12 is a coplanar line with a back surface ground, the same effect as the above-described microstrip line can be obtained.

[Fourth Embodiment]
Next, with reference to FIG. 6, the high frequency transmission line 10 concerning the 4th Embodiment of this invention is demonstrated. 6A and 6B are explanatory views showing the configuration of the high-frequency transmission line according to the fourth embodiment. FIG. 6A is a surface view, and FIG. 6B is a cross-sectional view taken along line EE in FIG. FIG. 6C is a rear view.
In the present embodiment, the signal line 12 is a differential line as the microstrip line in FIG.

  That is, in this embodiment, as shown in FIG. 6, the signal line 12 is composed of a pair of differential lines in which the normal phase signal line 16 and the negative phase signal line 17 are arranged in parallel to each other. The positive phase signal line 16 is a signal line through which a positive phase signal flows, and the straight portions 16X and 16Y are connected to each other through the bent portion 12Z. The negative phase signal line 17 is a signal line through which a negative phase signal having a phase opposite to that of the positive phase signal flows, and the straight portions 17X and 17Y are connected to each other through the bent portion 12Z.

  In this case, the normal phase signal line 16 and the negative phase signal line 17 can be regarded as one signal line 12. Therefore, the ground plane 13 on the back surface of the substrate 11 is positioned directly below the convex side angle P with respect to the bent portion 12Z of the signal line 12 including the positive phase signal line 16 and the reverse phase signal line 17, that is, on the convex side in the bent portion 12Z. An opening 14 is formed immediately below the convex side angle P of the negative phase signal line 17. Thereby, even if the signal line 12 is a differential line, the same effects as described above can be obtained.

  It is also conceivable that the line widths of the positive-phase signal line 16 and the negative-phase signal line 17 are wide and the capacitance component is biased to some extent between the convex side region and the concave side region of the respective bent portions. In such a case, the openings 14 may be formed in the ground plane 13 on the back surface of the substrate 11 immediately below the convex side corners of the normal phase signal line 16 and the negative phase signal line 17, respectively. Thereby, even if the signal line 12 is a differential line, the same effects as described above can be obtained.

[Extended embodiment]
The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. In addition, each embodiment can be implemented in any combination within a consistent range.

  DESCRIPTION OF SYMBOLS 10 ... High frequency transmission line, 11 ... Board | substrate, 12 ... Signal line, 12P ... Convex part, 12Q ... Concave part, 12R ... Notch part, 12X, 12Y ... Straight part, 12Z ... Bending part, 13 ... Ground plane, 14 ... Opening, 15 ... Surface ground, 16 ... Normal phase signal line, 16X, 16Y ... Linear part, 17 ... Reverse phase signal line, 17X, 17Y ... Linear part, M ... Virtual line, P ... Convex side angle, Q ... Concave side Corner, S ... Bottom, V ... Vertex, CP, CQ ... Capacitance component, LX, LY ... Inductance, TX, TY ... End.

Claims (6)

A high-frequency transmission line comprising a substrate, a signal line formed on the surface of the substrate, and a ground plane made of a ground conductor formed on the back surface of the substrate,
The signal line has a bent portion that connects two straight portions with different extending directions,
The high-frequency transmission line, wherein the ground plane has an opening from which the ground conductor located directly below the convex side corner of the bent portion is selectively removed. In the high frequency transmission line according to claim 1,
Of the capacitance component generated between the signal line of the bent portion and the ground plane, the first capacitance component generated in the convex portion that is a region on the convex side of the bent portion is the A high-frequency transmission line characterized in that it is smaller than a second electric capacity component generated in a concave side portion that is a region on the concave side corner of the bent portion. In the high frequency transmission line according to claim 1 or claim 2,
The opening is located on an imaginary line whose apex passes through the convex side angle and the concave side angle of the bent part in plan view, the base intersects the virtual line, and the apex angle is the bent part of the bent part. A high-frequency transmission line characterized by forming an isosceles triangle or an isosceles triangle substantially equal to an angle. In the high frequency transmission line according to any one of claims 1 to 3,
The high-frequency transmission line according to claim 1, wherein the signal line is a microstrip line or a coplanar line having a surface ground formed on a surface of the substrate. In the high frequency transmission line according to any one of claims 1 to 4,
The signal line is composed of a pair of differential lines in which a normal phase signal line and a negative phase signal line are arranged in parallel to each other,
The high-frequency transmission is characterized in that the opening is formed immediately below a convex-side angle of one of the positive-phase signal line and the negative-phase signal line that is located on the convex side in the bent portion. line. In the high frequency transmission line according to any one of claims 1 to 5,
The high-frequency transmission line according to claim 1, wherein the substrate comprises a laminated ceramic substrate in which a plurality of ceramic layers are laminated.

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