JP2009124475A - Impedance matching circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an impedance matching circuit in which dimensional design freedom of a transmission line can be ensured. <P>SOLUTION: The impedance matching circuit is provided with the transmission line 14 which is formed on one insulating substrate 12 and matches the impedance on the input side IN and on the output side OUT of high-frequency signals which are transmitted through the transmission line 14. In this case, the thickness W1 of the insulating substrate 12 on the input side IN and the thickness W2 of the insulating substrate 12 on the output side OUT are different. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an impedance matching circuit used in a high frequency circuit.

  In a high-frequency circuit in which a semiconductor device is connected to a transmission line, the characteristic impedance of the transmission line is generally 50Ω. Semiconductor devices are widely connected in parallel to transmission lines in order to ensure output power. In general, since the characteristic impedance of a semiconductor device is low, it has been widely performed to provide an impedance matching circuit between a transmission line and a semiconductor device (see, for example, Patent Document 1).

  The impedance matching circuit disclosed in Patent Document 1 includes a transmission line made of a microstrip line and a stub on a single ceramic substrate. However, this impedance matching circuit has a very low degree of design freedom because the dimensions of the stub and the transmission line are almost uniquely determined by the frequency of the high frequency signal, the thickness and dielectric constant of the ceramic substrate, and the impedance to be matched.

  In order to solve this problem, a technique for forming an impedance matching circuit using two substrates having different dielectric constants is disclosed (for example, see Non-Patent Document 1).

The impedance matching circuit disclosed in Non-Patent Document 1 forms an impedance matching circuit across two substrates having different dielectric constants connected to each other by a gold wire. By configuring in this way, the degree of freedom in design of the impedance matching circuit is surely improved.
JP-A-6-6151 Mitsubishi Electric Technical Report Vol. 78, no. 3,2004, pp42-45

However, in the impedance matching circuit of Non-Patent Document 1,
(1) The number of manufacturing steps increases as the number of parts constituting the impedance matching circuit increases. (2) It is necessary to accurately align the two substrates constituting the impedance matching circuit. (3) Impedance In designing the matching circuit, it is necessary to consider an extra inductance component derived from the gold wire used to connect the two boards. (4) The cost increases by using two boards with different dielectric constants. Problems occur.

  As a result of intensive studies, the inventors have conceived that the problems (1) to (4) described above can be solved by changing the thickness of the substrate of the impedance matching circuit between the input side and the output side.

  Accordingly, an object of the present invention is to provide an impedance matching circuit that solves the problems (1) to (4) described above while ensuring a degree of freedom in design.

  In order to achieve the above object, an impedance matching circuit according to the present invention includes a transmission line formed on a single insulating substrate, and has impedances on the input side and output side of a high-frequency signal transmitted through the transmission line. Align. Here, the thickness of the insulating substrate on the input side is different from the thickness of the insulating substrate on the output side.

  With this configuration, the effective dielectric constant of the insulating substrate can be changed between the high-frequency signal input side and the output side.

  That is, the same effect as the impedance matching circuit composed of two substrates having different dielectric constants disclosed in Non-Patent Document 1 described above can be obtained.

  Here, the “thickness of the insulating substrate” indicates the length of the insulating substrate measured along the direction perpendicular to the main surface of the insulating substrate on which the transmission line extends.

  In the implementation of the impedance matching circuit described above, it is preferable that the thickness of the insulating substrate changes stepwise from the input side to the output side.

  Moreover, it is preferable that the transmission line branches from the input side to the output side.

  With this configuration, when a plurality of semiconductor devices are connected in parallel to the thin output side, the width of the transmission line connected to each semiconductor device can be reduced. As the width of each transmission line becomes narrow, as a result, the entire width of the impedance matching circuit can be reduced.

  In the present invention, the thickness of the insulating substrate used in the impedance matching circuit is different between the input side and the output side of the high-frequency signal. As a result, by changing the thickness of the substrate, the impedance can be changed between the input side and the output side in accordance with the manner of change in the thickness.

  More specifically, if the thickness of the insulating substrate is increased, the width of the transmission line orthogonal to the propagation direction of the high-frequency signal (hereinafter simply referred to as “transmission line width”) without changing the characteristic impedance. Can be widened). On the contrary, if the thickness of the insulating substrate is reduced, the width of the transmission line can be reduced without changing the characteristic impedance.

  In other words, when the width of the transmission line is wide and protrudes from the desired substrate size, the width of the transmission line can be reduced without changing the characteristic impedance by reducing the thickness of the substrate. As a result, the impedance matching circuit can be accommodated within a desired substrate size.

  That is, in the present invention, the thickness of the substrate is changed without being constant in one insulating substrate. Thus, the thickness of the substrate is set as one of the parameters for adjusting the characteristic impedance and the width of the transmission line. As described above, in the impedance matching circuit, by adding “the thickness of two or more substrates” to the design parameter, the width of the transmission line can be changed more flexibly than in the past.

  Embodiments of the present invention will be described below with reference to the drawings. Each drawing is merely a schematic representation of the shape, size, and arrangement relationship of each component to the extent that the present invention can be understood. Moreover, although the preferable structural example of this invention is demonstrated hereafter, the material of each component, a numerical condition, etc. are only a suitable example. Therefore, the present invention is not limited to the following embodiments. Moreover, in each figure, the same code | symbol is attached | subjected to a common component and the description may be abbreviate | omitted.

(Embodiment 1)
FIG. 1 is a perspective view schematically showing a configuration of an impedance matching circuit.

  The impedance matching circuit 10 of this embodiment includes a transmission line 14 formed on a single insulating substrate 12. And it has the function to match the impedance of the input side IN and output side OUT of the high frequency signal transmitted through the transmission line 14. Furthermore, the thickness of the insulating substrate 12 on the input side IN is different from the thickness of the insulating substrate 12 on the output side OUT.

  More specifically, the impedance matching circuit 10 includes a microstrip line. A metal film 16 is formed on the second main surface of the insulating substrate 12, that is, the entire back surface 12b. A transmission line 14 as a metal film patterned into a predetermined shape is formed on the first main surface, that is, the upper surface 12 a of the insulating substrate 12.

  As shown in FIG. 1, the insulating substrate 12 is made of a rectangular plate-shaped ceramic. Here, as the ceramic, for example, a substrate having a dielectric constant of 5 to 200 is preferably used.

  Further, as shown in FIG. 1, the insulating substrate 12 has a stepped thickness decreasing from the input side IN to the output side OUT. Specifically, the thickness of the insulating substrate 12 changes discontinuously at the stepped portion 12c. In the insulating substrate 12, a portion located on the input side IN and having a large thickness is referred to as “upper stage 12H”, and a portion located on the output side OUT and having a small thickness is referred to as “lower stage 12L”. Note that the thickness h1 of the upper stage 12H is preferably about 60 to 510 μm, for example, and the thickness h2 of the lower stage 12L is preferably about 50 to 500 μm, for example. When the insulating substrate 12 is formed in two discontinuous thicknesses, the transmission line 14 extends over the upper surface 12Ha of the upper step 12H, the step surface 12ca of the stepped portion 12c, and the upper surface 12La of the lower step 12L. Formed continuously.

  As is clear from FIG. 1, the transmission line 14 is branched into two from the input side IN to the output side OUT. More specifically, the transmission line 14 includes an upper line 14H provided in the upper stage 12H, connection lines 14C and 14C provided in the step part 12c, and lower stage lines 14L and 14L provided in the lower stage 12L. ing. Here, as the transmission line 14, for example, a gold thin film having a constant thickness is preferably used.

  The upper line 14H extends from the input terminal 14a to which a high frequency signal from an external circuit (not shown) is input, to the upper surface 12Ha of the upper stage 12H. And it branches into two in the branch part 14b provided in the edge part on the opposite side to the input side IN of the upper stage 12H. Note that the width in the direction perpendicular to the propagation direction of the high-frequency signal on the upper line 14H and parallel to the upper surface 12Ha is equal regardless of the location, and is W1.

  The connection lines 14C and 14C are transmission lines provided on the step surface 12ca of the step portion 12c, that is, a vertical wall surface. The connection lines 14C and 14C electrically connect the upper line 14H branched in two at the branching portion 14b to the lower lines 14L and 14L, respectively. Since the lower lines 14L and 14L are formed on the upper surface 12La of the lower stage 12L, which is thinner than the upper stage 12H, the width W2 perpendicular to the propagation direction of the high-frequency signal and parallel to the upper surface 12Ha is greater than W1. It is designed narrowly. Therefore, the connection lines 14C and 14C have a width from W1 from the upper stage 12H to the lower stage 12L in order to connect the upper stage line 14H having a width W1 and the lower stage lines 14L and 14L having a width W2 (<W1). It is formed to narrow in a tapered shape toward W2.

  The lower stage lines 14L and 14L are electrically connected to the connection lines 14C and 14C, and extend over the upper surface 12La of the lower stage 12L. On the output side OUT of the upper surface 12La of the lower stage 12L, stubs 14c and 14c for outputting a high-frequency signal propagating through the impedance matching circuit 10 to a semiconductor device (not shown) are provided. The stubs 14c and 14c are widened from the ends of the lower-stage lines 14L and 14L to form the transmission line 14 in a rectangular shape, and are electrically connected to the lower-stage lines 14L and 14L, respectively. Note that the widths W2 of the lower lines 14L and 14L are equal regardless of the location.

  Subsequently, in the impedance matching circuit 10 of this embodiment, an effect produced by changing the thickness of the insulating substrate 12 will be described.

In a general microstrip line as shown in FIG. 2, the following well-known relationship is established among the characteristic impedance Z0, the width W of the transmission line 14, and the thickness h of the insulating substrate 12. It has been known.
If W / h <1:
Z ₀ = (60 / εff ^0.5 ) ln (8h / W + 0.25W / h) (1)
εff = (εr + 1) / 2 + [(1 + 12h / W) ^−0.5 + 0.04 (1-W / h) ² ] × (εr−1) / 2 (2)
When W / h ≧ 1:
Z ₀ = 120π / [εff ^0.5 × (W / h + 1.393 + 0.667ln (W / h + 1.444)] (3)
εff = (εr + 1) + (1 + 12h / W) ^−0.5 × (εr−1) / 2 (4)
Note) In the equations (1) to (4), εr is the dielectric constant of the insulating substrate 12.

In addition, in the equations (1) to (4), the constants are included in the constants, but as parameters for determining the characteristic impedance Z ₀ , in addition to W and h, the frequency of the high frequency signal, the thickness of the transmission line, Exists.

According to these equations, when the characteristic impedance Z ₀ is constant, if the thickness h of the insulating substrate 12 is large, the width W of the transmission line 14 is large, and if the thickness h of the insulating substrate 12 is small, It can be seen that the width W of the transmission line 14 is reduced.

  This indicates that by reducing the thickness of the insulating substrate 12, the width of the transmission line 14 can be reduced while keeping the characteristic impedance constant. That is, in the case of the impedance matching circuit 10 of this embodiment, the width of the lower line 14L formed in the lower stage 12L having the thickness h2 smaller than the width W1 of the upper stage 14H formed in the upper stage 12H having the thickness h1. W2 can be reduced (W1> W2).

  Although detailed description is omitted, the above discussion can be applied not only to the transmission line 14 but also to the stub 14c. That is, by reducing the thickness of the insulating substrate 12, the width of the stub (the length of the stub orthogonal to the propagation direction of the high-frequency signal) can be reduced.

Specific numerical values will be given from simulations using the equations (1) to (4). For example, the frequency of the high-frequency signal propagating through the impedance matching circuit 10 is 2 GHz. The characteristic impedance Z ₀ to be matched is 3.7Ω, the dielectric constant εr of the insulating substrate is 40, and the thickness d of the transmission line 14 (the transmission measured perpendicular to the first main surface 12a of the insulating substrate 12). The length of the line 14) is 4 μm.

  Under this simulation condition, when the thickness h of the insulating substrate 12 is 200 μm, in order to obtain a characteristic impedance of 3.7Ω, the width W of the transmission line 14 is reduced from the expressions (3) and (4) by about It turns out that it is necessary to set it as 2 mm. On the other hand, when the thickness h of the insulating substrate 12 is changed to 100 μm, in order to obtain a characteristic impedance of 3.7Ω, the width W of the transmission line 14 is approximately equal to the expression (3) and (4). It can be seen that 1 mm is sufficient.

  If this simulation result is applied to the impedance matching circuit 10 of this embodiment, the width W1 of the upper circuit 14H of the upper stage 12H (thickness h1 = 200 μm) is 2 mm. Further, the width W2 of the lower circuit 14L of the lower stage 12L (thickness h2 = 100 μm) is 1 mm.

  That is, by reducing the thickness h2 of the lower stage 12L, the width can be reduced by 2 mm in total as the two lower stage circuits 14L and 14L. Further, the stubs 14c and 14c can be expected to have a size reduction effect of the same size or more.

  As is apparent from FIG. 1, the overall dimensions of the impedance matching circuit 10 are mainly regulated by the sizes of the lower circuits 14L and 14L and the stubs 14c and 14c. Therefore, the size of the lower stage circuits 14L and 14L and the stubs 14c and 14c is reduced, so that the impedance matching circuit 10 can be reduced in size as compared with a uniform thickness h1.

  Next, with reference to FIG. 3, the manufacturing method of the impedance matching circuit of this embodiment will be described.

  First, as shown in FIG. 3 (A), a ceramic substrate 18 is prepared, and a substrate portion 18N that covers a hatched portion in FIG. 3 (A), that is, a portion to be the lower stage 12L, is polished. The insulating substrate 12 having the stepped portion 12c and the lower step 12L is formed.

  Subsequently, as shown in FIG. 3B, a photoresist pattern 24 is formed in which the precursor region 14d to be the transmission line 14 is exposed on the first main surface 12a of the insulating substrate 12, that is, the exposed surface on the upper surface side. The precursor substrate 23 thus formed is formed. That is, the photoresist is applied to the entire surface of the first main surface 12a of the insulating substrate 12, that is, the upper surface 12Ha of the upper stage 12H, the step surface 12ca of the stepped part 12C, and the upper surface 12La of the lower stage 12L. Thereafter, exposure and development are performed using a mask on which the pattern shape of the transmission line 14 is drawn to form a photoresist pattern 24.

  Subsequently, as shown in FIG. 3C, the precursor substrate 23 on which the photoresist pattern is formed is dipped in a gold plating solution to perform gold plating. Thereafter, an unnecessary photoresist pattern is removed to form the transmission line 14 extending over the upper stage 12H and the lower stage 12L. Thereby, the impedance matching circuit 10 as shown in FIG. 1 is completed.

  Thus, in the impedance matching circuit 10 of this embodiment, the transmission line 14 is formed so as to straddle the insulating substrate 12 whose thickness changes stepwise. As a result, the impedance can be changed between the input side and the output side by changing the thickness of the substrate.

  Further, when the transmission line 14 is wide and protrudes from a desired substrate size, the width of the transmission line can be reduced without changing the characteristic impedance by reducing the thickness of the insulating substrate 12. Can be accommodated within a desired substrate size.

  In addition, the four problems in the impedance matching circuit of Non-Patent Document 1 described above ((1) increase in the number of parts, (2) necessity of accurate alignment, (3) generation of extra inductance, and (4) increase in cost. ) Can be solved.

  Next, a modification of the present invention will be described.

  In the impedance matching circuit 10 shown in FIG. 1, the transmission line 14 is branched into two from the upper stage 12H to the lower stage 12L. However, the number of branches of the transmission line is not limited to two. For example, as shown in FIG. 4A, the thickness of the insulating substrate 12 may be changed in three stages of the upper stage 12H, the middle stage 12M, and the lower stage 12L, and the transmission line 20 may be branched into four branches.

  Moreover, in this embodiment, the case where the thickness of the insulating substrate 12 was changed stepwise was explained. However, the thickness of the insulating substrate 12 is not limited to a case where the thickness changes stepwise as long as the object of the present invention is achieved. For example, as shown in FIG. 4B, an insulating substrate 22 whose thickness decreases linearly from the input side IN to the output side OUT may be formed. In that case, it is preferable to continuously change the width of the transmission line 14 in accordance with the thickness of the substrate. Moreover, you may form so that the thickness of the insulating board | substrate 12 may reduce along a curve (for example, circular arc).

  In this embodiment, the case where the ceramic substrate 18 is used as the insulating substrate 12 has been described. However, as the insulating substrate 12, a semiconductor substrate such as Si or GaAs can be used.

  Further, in this embodiment, the case where a part of the ceramic substrate 18 having a uniform thickness is polished and thinned in manufacturing the impedance matching circuit 10 has been described. However, by increasing the number of stacked green sheets in the portion to be the upper stage 12H and forming the substrate precursor with the reduced number of stacked green sheets in the portion to be the lower stage 12L, by firing this substrate precursor The ceramic substrate 18 may be formed.

It is a perspective view which shows typically the structure of the impedance matching circuit of this embodiment. It is a perspective view with which it uses for description of a general microstrip line. (A)-(C) are process drawings with which it uses for description of the manufacturing process of the impedance matching circuit of this embodiment. (A) is a perspective view which shows the modification of an impedance matching circuit. (B) is a perspective view showing another modification of the impedance matching circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Impedance matching circuit 12 Insulating board | substrate 12a 1st main surface 12b 2nd main surface 12c Step part 12ca Step surface 12H Upper stage 12M Middle stage 12L Lower stage 14,20 Transmission line 14a Input end 14b Branch part 14c Stub 14C Connection line 14H Upper stage line 14L Lower line 16 Metal film 18 Ceramic substrate IN Input side OUT Output side

Claims (3)

An impedance matching circuit comprising a transmission line formed on a single insulating substrate and matching impedances of an input side and an output side of a high-frequency signal transmitted through the transmission line,
The impedance matching circuit, wherein a thickness of the insulating substrate on the input side is different from a thickness of the insulating substrate on the output side.   2. The impedance matching circuit according to claim 1, wherein the thickness of the insulating substrate changes stepwise from the input side to the output side. The impedance matching circuit according to claim 1, wherein the transmission line branches from the input side to the output side.

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