Transmission line transformer and amplifying circuit

A first transmission line and a second transmission line that are connected in series to each other are disposed at different positions in a thickness direction of a substrate. A third transmission line is disposed between the first transmission line and the second transmission line in the thickness direction of the substrate. The third transmission line includes a first end portion connected to one end portion of the first transmission line, and a second end portion that is AC-grounded. The first transmission line and the second transmission line are electromagnetically coupled to the third transmission line.

This application claims priority from Japanese Patent Application No. 2018-164417 filed on Sep. 3, 2018, and claims priority from Japanese Patent Application No. 2019-112969 filed on Jun. 18, 2019. The content of this application is incorporated herein by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure relates to a transmission line transformer and an amplifying circuit.

2. Description of the Related Art

There has been available a technique of using a transmission line transformer as an impedance matching circuit that is disposed between an output terminal of an amplifier and a load (U.S. Pat. No. 8,384,484). The transmission line transformer disclosed in U.S. Pat. No. 8,384,484 is constituted by two broadside-coupled transmission lines. In the configuration disclosed in U.S. Pat. No. 8,384,484, a plurality of transmission line transformers are cascade-connected to achieve a desired impedance transformation ratio. A basic transmission line transformer is described in “Chapter Six Transmission Line Transformers”, Radio Frequency Circuit Design, Second Edition, by W. Alan Davis, Copyright (C) 2011 John Wiley & Sons, Inc.

BRIEF SUMMARY OF THE DISCLOSURE

In the configuration disclosed in U.S. Pat. No. 8,384,484, a plurality of transmission line transformers are cascade-connected to achieve a desired impedance transformation ratio because it is difficult to achieve a large impedance transformation ratio with a single transmission line transformer. This configuration leads to difficulty in reducing the size of the impedance matching circuit.

An object of the present disclosure is to provide a transmission line transformer capable of achieving a larger impedance transformation ratio than that in a transmission line transformer according to the related art. Another object of the present disclosure is to provide an amplifying circuit including the transmission line transformer.

According to preferred embodiments of the present disclosure, a transmission line transformer includes: a first transmission line and a second transmission line that are disposed at different positions in a thickness direction of a substrate and that are connected in series to each other; and a third transmission line that is disposed between the first transmission line and the second transmission line in the thickness direction of the substrate, that includes a first end portion connected to one end portion of the first transmission line, and that includes a second end portion that is AC-grounded. The first transmission line and the second transmission line are electromagnetically coupled to the third transmission line.

According to other preferred embodiments of the present disclosure, an amplifying circuit includes: an amplifying element that amplifies a high-frequency signal; and a transmission line transformer connected to an input terminal of the amplifying element or an output terminal of the amplifying element. The transmission line transformer includes: a first transmission line and a second transmission line that are disposed at different positions in a thickness direction of a substrate and that are connected in series to each other; and a third transmission line that is disposed between the first transmission line and the second transmission line in the thickness direction of the substrate, that includes a first end portion connected to one end portion of the first transmission line, the one end portion being connected to the amplifying element, and that includes a second end portion that is AC-grounded. The first transmission line and the second transmission line are electromagnetically coupled to the third transmission line.

An impedance transformation ratio larger than that in the related art can be obtained by using a single transmission line transformer. Thus, an impedance matching circuit constituted by the transmission line transformer can be reduced in size.

DETAILED DESCRIPTION OF THE DISCLOSURE

First Embodiment

A transmission line transformer according to a first embodiment will be described with reference toFIGS.1A,1B, and1C.

FIG.1Ais a schematic diagram for describing the operation principle of a transmission line transformer20according to the first embodiment. The transmission line transformer20according to the first embodiment includes a first transmission line21, a second transmission line22, and a third transmission line23that are disposed on a surface of a substrate or inside the substrate. The vertical direction inFIG.1Acorresponds to the thickness direction of the substrate. The first transmission line21and the second transmission line22are disposed at different positions in the thickness direction of the substrate. The third transmission line23is disposed between the first transmission line21and the second transmission line22in the thickness direction of the substrate.

One end portion of the third transmission line23is referred to as a first end portion23A, and the other end portion thereof is referred to as a second end portion23B. One end portion of the first transmission line21is referred to as a third end portion21A, and the other end portion thereof is referred to as a fourth end portion21B. One end portion of the second transmission line22is referred to as a fifth end portion22A, and the other end portion thereof is referred to as a sixth end portion22B. The first end portion23A of the third transmission line23is connected to the third end portion21A of the first transmission line21, and the second end portion23B is grounded. Here, “grounding” includes both DC grounding and AC grounding. The third end portion21A of the first transmission line21is connected to a first terminal31for connecting to an external circuit. The fourth end portion21B of the first transmission line21is connected to the fifth end portion22A of the second transmission line22. The sixth end portion22B of the second transmission line22is connected to a second terminal32for connecting to an external circuit. That is, the first transmission line21and the second transmission line22are connected in series to each other to form a transmission line, and both ends of the transmission line correspond to the first terminal31and the second terminal32.

The first transmission line21and the second transmission line22are each electromagnetically coupled to the third transmission line23. In the first embodiment, the coupling between the first transmission line21and the third transmission line23corresponds to the coupling between coils having the same number of turns T, and also the coupling between the second transmission line22and the third transmission line23corresponds to the coupling between coils having the same number of turns T. For example, all of the first transmission line21, the second transmission line22, and the third transmission line23have the number of turns T equal to n.

Next, the definition of the number of turns T in this specification will be described with reference toFIGS.2A and2B.

FIG.2Ais a diagram illustrating an example of a coil pattern. An X-Y orthogonal coordinate system is defined in which an outer end portion of the coil pattern is an origin point O. This coil pattern has a path extending from the origin point O to an end point E, which is an inner end portion of the coil pattern. The path length from the origin point O to a point P on the coil pattern is represented by L. The Euclidean distance from the origin point O to the coordinates of the point P is represented by D.

FIG.2Bis a graph illustrating the relationship between the path length L and the Euclidean distance D at each point from the origin point O to the end point E of the coil pattern. In the coil pattern illustrated inFIG.2A, the Euclidean distance D has a first maximum value at a point P1, has a minimum value at a point P2, and has a second maximum value at a point P3 before the end point E. The number of maximum values in the graph illustrating the relationship between the path length L and the Euclidean distance D is defined as the number of turns T of the coil pattern. The number of turns T of the coil pattern illustrated inFIG.2Ais 2.

The alternating currents flowing through the first transmission line21, the second transmission line22, and the third transmission line23will be described. The current flowing from the first terminal31toward the second terminal32first flows through the first transmission line21from the third end portion21A toward the fourth end portion21B, and then flows through the second transmission line22from the fifth end portion22A toward the sixth end portion22B. The magnitude of the alternating current flowing through the first transmission line21is equal to the magnitude of the alternating current flowing through the second transmission line22. The alternating current flowing through the first transmission line21induces an odd-mode current flowing through the third transmission line23from the first end portion23A toward the second end portion23B, and the alternating current flowing through the second transmission line22induces an odd-mode current flowing through the third transmission line23from the first end portion23A toward the second end portion23B. The direction in which the odd-mode current induced in the third transmission line23flows is opposite to the direction in which the alternating current flows through the first transmission line21and the second transmission line22. The odd-mode current induced by the current flowing through the first transmission line21and the odd-mode current induced by the current flowing through the second transmission line22are equal to each other in terms of the magnitude and the direction.

The odd-mode current induced by the current flowing through the first transmission line21and the odd-mode current induced by the current flowing through the second transmission line22flow through the third transmission line23in a superimposed manner. Thus, the magnitude of the odd-mode current induced in the third transmission line23is twice as much as the magnitude of the current flowing through a series circuit formed of the first transmission line21and the second transmission line22. When the magnitude of the current flowing from the first terminal31into the transmission line transformer20is represented by i, the magnitude of the current flowing through the series circuit formed of the first transmission line21and the second transmission line22is represented by (⅓)i, and the magnitude of the current flowing through the third transmission line23is represented by (⅔)i. The magnitude of the current outputted from the second terminal32is represented by (⅓)i.

Next, voltages will be described. The voltage at the first terminal31is represented by v1, and the voltage at the second terminal32is represented by v2. The voltage at the third end portion21A of the first transmission line21and the voltage at the first end portion23A of the third transmission line23are equal to the voltage v1 at the first terminal31. The voltage at the sixth end portion22B of the second transmission line22is equal to the voltage v2 at the second terminal32. The voltage at the fourth end portion21B of the first transmission line21is represented by v3. The voltage at the fifth end portion22A of the second transmission line22is equal to the voltage v3 at the fourth end portion21B of the first transmission line21. The voltage at the second end portion23B of the third transmission line23is 0 V.

The potential difference between the third end portion21A and the fourth end portion21B of the first transmission line21is equal to the potential difference between the second end portion23B and the first end portion23A of the third transmission line23, and thus v1−v3=0−v1 holds. Similarly, v3−v2=0−v1 holds between the second transmission line22and the third transmission line23. The solution of the simultaneous equations is 3×v1=v2. In other words, the voltage v2 at the second terminal32is three times as much as the voltage v1 at the first terminal31.

When a load with an impedance R2 is connected to the second terminal32, v2=(⅓)i×R2 holds. The impedance seen on the load side from the first terminal31is represented by R1, and then v1=R1×i holds. The solution of these equations is R1=( 1/9)R2. In other words, the impedance R1 seen on the load side from the first terminal31is 1/9 times as much as the impedance R2 of the load connected to the second terminal32. On the other hand, when a load is connected to the first terminal31, the impedance seen on the load side from the second terminal32is 9 times as much as the impedance of the load connected to the first terminal31. In this way, the transmission line transformer20according to the first embodiment functions as an impedance transformation circuit having an impedance transformation ratio of about 9.

FIG.1Bis a schematic perspective view of the transmission line transformer20according to the first embodiment, andFIG.1Cis a cross-sectional view taken along a dot-and-dash line1C inFIG.1B.

The first transmission line21and the second transmission line22are disposed at different positions in the thickness direction of a substrate30(FIG.1C). The substrate30may be made of, for example, a magnetic insulating material or a dielectric material. Examples of a substrate made of a dielectric material include a resin substrate and a ceramic substrate. Alternatively, an insulating layer formed on a semiconductor substrate may be used as the substrate30. The third transmission line23is disposed between the first transmission line21and the second transmission line22. The first transmission line21, the second transmission line22, and the third transmission line23are each constituted by a substantially spiral conductor pattern whose dimension is larger in the width direction than in the thickness direction. In addition, an extended line24and a ground conductor35(FIG.1B) are disposed in the substrate30.

The third end portion21A of the first transmission line21, the first end portion23A of the third transmission line23, and the sixth end portion22B of the second transmission line22are disposed at positions that overlap each other in plan view. The fourth end portion21B of the first transmission line21and the fifth end portion22A of the second transmission line22are disposed at positions that overlap each other in plan view. In the same layer as the third transmission line23, a conductor pattern29is disposed at the position corresponding to the fourth end portion21B of the first transmission line21. A via conductor25connects the third end portion21A of the first transmission line21and the first end portion23A of the third transmission line23. A via conductor26connects the fourth end portion21B of the first transmission line21and the conductor pattern29, and a via conductor27connects the conductor pattern29and the fifth end portion22A of the second transmission line22. A via conductor28connects the sixth end portion22B of the second transmission line22and the extended line24. The third end portion21A of the first transmission line21is connected to the first terminal31, and the extended line24is connected to the second terminal32. The second end portion23B of the third transmission line23is connected to the ground conductor35.

In plan view, the first transmission line21extends to turn in a first turn direction (counterclockwise inFIG.1B) from the third end portion21A. The third transmission line23extends to turn in a second turn direction (clockwise inFIG.1B), which is opposite to the first turn direction, from the first end portion23A. The second transmission line22extends to turn in the first turn direction from the fifth end portion22A.

In plan view, a substantially square-shaped closed virtual loop36is defined. The third end portion21A of the first transmission line21, the first end portion23A of the third transmission line23, and the sixth end portion22B of the second transmission line22are disposed at the same position on the loop36in plan view. The fourth end portion21B of the first transmission line21, the conductor pattern29, and the fifth end portion22A of the second transmission line22are disposed at the same position inside the loop36in plan view. The third end portion21A, the first end portion23A, and the sixth end portion22B may be disposed so as to partially overlap each other in plan view. Similarly, the fourth end portion21B, the conductor pattern29, and the fifth end portion22A may be disposed so as to partially overlap each other in plan view.

The first transmission line21extends about one round along the loop36in the first turn direction from the third end portion21A, and extends inward from the loop36to reach the fourth end portion21B. The third transmission line23extends about one round along the loop36in the second turn direction from the first end portion23A, and extends outward from the loop36to reach the second end portion23B. The second transmission line22extends from the fifth end portion22A located inside the loop36toward the loop36, and extends about one round along the loop36in the first turn direction to reach the sixth end portion22B. In this way, the first transmission line21, the second transmission line22, and the third transmission line23each constitute a coil pattern whose number of turns T is 1.

In the first transmission line21, the second transmission line22, and the third transmission line23, the portions along the loop36overlap each other at least partially in plan view. Thus, the first transmission line21is capacitively coupled to the third transmission line23, and also the second transmission line22is capacitively coupled to the third transmission line23.

Next, excellent effects of the first embodiment will be described.

A transmission line transformer having a two-layer structure formed of the first transmission line21and the third transmission line23has an impedance transformation ratio of about 4. In contrast, the transmission line transformer20according to the first embodiment has an impedance transformation ratio of about 9, which is larger than the impedance transformation ratio of the transmission line transformer having a two-layer structure. This is because the electromagnetic coupling of the third transmission line23with both the first transmission line21and the second transmission line22doubles the odd-mode current induced in the third transmission line23.

Furthermore, because the first transmission line21, the second transmission line22, and the third transmission line23are disposed so as to substantially overlap each other in plan view, an increase in the impedance transformation ratio does not cause an increase in the area occupied by the transmission line transformer20in the substrate30. Thus, the size of the transmission line transformer20can be reduced compared to the configuration of achieving a large impedance transformation ratio by cascade-connecting a plurality of transmission line transformers each having a small impedance transformation ratio.

Next, a transmission line transformer according to a modification example of the first embodiment will be described.

In the first embodiment, the loop36(FIG.1B) along which the first transmission line21, the second transmission line22, and the third transmission line23extend is substantially square-shaped. Alternatively, the loop36may have another shape. For example, the loop36may be substantially circular, elliptical, rectangular, polygonal, or the like. In the first embodiment, the series circuit formed of the first transmission line21and the second transmission line22extends to turn counterclockwise from the third end portion21A, and the third transmission line23extends to turn clockwise. Alternatively, these turn directions may be reversed.

In the first embodiment, the first transmission line21, the second transmission line22, and the third transmission line23each extend about one round along the loop36. In each of the first transmission line21, the second transmission line22, and the third transmission line23, the length of the portion along the loop36may be shorter than the length of the one round. Even with this structure, the number of turns T can be 1 according to the definition of the number of turns T in this specification (FIGS.2A and2B). To achieve sufficient electromagnetic coupling, it is preferable that the number of turns T be 1 or more in each of the first transmission line21, the second transmission line22, and the third transmission line23.

In the first embodiment, the conductor patterns constituting the first transmission line21, the second transmission line22, and the third transmission line23have widths that are substantially equal to each other.

Alternatively, the conductor pattern of the third transmission line23may have a width larger than or equal to the width of each of the first transmission line21and the second transmission line22. In this case, the conductor pattern of the first transmission line21and the conductor pattern of the second transmission line22may preferably be disposed inside the conductor pattern of the third transmission line23in the width direction of the conductor patterns in plan view. This arrangement enables the capacitive coupling between the first transmission line21and the third transmission line23and the capacitive coupling between the second transmission line22and the third transmission line23to be increased. The increase in the capacitive coupling makes it possible to reduce loss when inducing an odd-mode current in the third transmission line23. As a result, insertion loss is reduced, and an impedance transformation ratio closer to a theoretical transformation ratio is obtained.

In the first embodiment, as illustrated inFIG.1B, the extended line24is disposed in a layer different from the layer of the second transmission line22, and the second transmission line22and the second terminal32are connected to each other with the extended line24interposed therebetween. Alternatively, the extended line24and the second transmission line22may be disposed in the same layer. In this configuration, the second transmission line22and the extended line24are formed of a common conductor pattern, and thus the sixth end portion22B of the second transmission line22is not clearly specified. In this case, a portion at which the second transmission line22deviates from the loop36may be defined as the sixth end portion22B.

In the first embodiment, as illustrated inFIG.1B, the end of the portion extending outward from the portion along the loop36of the third transmission line23is defined as the second end portion23B. Alternatively, the end of the portion along the loop36may be defined as the second end portion23B, and the portion extending from the second end portion23B to the ground conductor35may be regarded as a part of the extended line24.

Similarly, the end of the portion along the loop36of the first transmission line21may be defined as the fourth end portion21B, and the portion extending inward from the loop36from the fourth end portion21B may be regarded as a wiring line that connects the first transmission line21and the second transmission line22. Similarly, the end of the portion along the loop36of the second transmission line22may be defined as the fifth end portion22A, and the portion extending inward from the loop36from the fifth end portion22A may be regarded as a wiring line that connects the first transmission line21and the second transmission line22.

Second Embodiment

A transmission line transformer20according to a second embodiment will be described with reference toFIGS.3A and3B. The same components as those of the transmission line transformer20according to the first embodiment will not be described.

FIG.3Ais a schematic diagram for describing the operation principle of the transmission line transformer20according to the second embodiment. In the first embodiment, the first transmission line21, the second transmission line22, and the third transmission line23have the same number of turns T. In the second embodiment, the number of turns T of each of the first transmission line21and the third transmission line23is n, whereas the number of turns T of the second transmission line22is 2n. That is, the number of turns T of the second transmission line22is twice as many as the number of turns T of each of the first transmission line21and the third transmission line23.

In this case, the magnitude of the odd-mode current induced in the third transmission line23by the alternating current flowing through the second transmission line22is twice as much as the magnitude of the alternating current flowing through the second transmission line22. Also, an odd-mode current is induced in the third transmission line23by the alternating current flowing through the first transmission line21, as in the first embodiment. Thus, the magnitude of the odd-mode current induced in the third transmission line23is three times as much as the magnitude of the alternating current flowing through the series circuit formed of the first transmission line21and the second transmission line22. When the magnitude of the current flowing from the first terminal31into the transmission line transformer20is represented by i, the magnitude of the current flowing through the series circuit formed of the first transmission line21and the second transmission line22is represented by (¼)i, and the magnitude of the current flowing through the third transmission line23is represented by (¾)i. The magnitude of the current outputted from the second terminal32is represented by (¼)i.

Regarding the voltages, v1−v3=0−v1 holds between the first transmission line21and the third transmission line23, as in the first embodiment. 2(0−v1)=v3−v2 holds between the second transmission line22and the third transmission line23. The solution of the simultaneous equations is v2=4×v1. That is, the voltage v2 at the second terminal32is four times as much as the voltage v1 at the first terminal31.

When a load is connected to the second terminal32, the impedance seen on the load side from the first terminal31is 1/16 times as much as the impedance of the load connected to the second terminal32. On the other hand, when a load is connected to the first terminal31, the impedance seen on the load side from the second terminal32is 16 times as much as the impedance of the load connected to the first terminal31. In this way, the transmission line transformer20according to the second embodiment functions as an impedance transformation circuit having an impedance transformation ratio of about 16.

FIG.3Bis a schematic perspective view of the transmission line transformer20according to the second embodiment. In the first embodiment, the second transmission line22(FIG.1B) extends about one round counterclockwise along the loop36from the fifth end portion22A. In contrast, in the second embodiment, the second transmission line22extends about two rounds counterclockwise along the loop36from the fifth end portion22A. Thus, the number of turns T of the second transmission line22is twice as many as the number of turns T of the third transmission line23. When calculating the number of turns T of the second transmission line22, the method described above with reference toFIGS.2A and2Bis applied, with the sixth end portion22B, which is the outer end portion, being the origin point. Because the number of turns T of the second transmission line22is 2, the width of the second transmission line22is smaller than the width of each of the first transmission line21and the third transmission line23.

Next, excellent effects of the second embodiment will be described.

In the second embodiment, the number of turns T of the second transmission line22is twice as many as the number of turns T of the third transmission line23, and accordingly the impedance transformation ratio is increased to about 16. Also in the second embodiment, the first transmission line21, the second transmission line22, and the third transmission line23are disposed so as to overlap each other in plan view, which makes it possible to suppress an increase in the area occupied by the transmission line transformer20in the substrate30. In this way, an impedance transformation circuit with a large impedance transformation ratio can be obtained while suppressing an increase in the size of the circuit.

Next, a transmission line transformer20according to a modification example of the second embodiment will be described with reference toFIG.4.

FIG.4is a schematic perspective view of the transmission line transformer20according to this modification example of the second embodiment. In this modification example, the second transmission line22is constituted by a set of two coil patterns221and222. The coil patterns221and222each have the same shape as that of the second transmission line22according to the second embodiment (FIG.3B) in plan view. The coil pattern221is disposed at the same position and in the same posture as those of the second transmission line22of the transmission line transformer20according to the second embodiment (FIG.3B).

The coil pattern222is disposed across the coil pattern221from the third transmission line23in the thickness direction such that the coil pattern222overlaps the coil pattern221in plan view.

A via conductor225connects a fifth end portion221A of the coil pattern221and a fifth end portion222A of the coil pattern222. A via conductor226connects a sixth end portion221B of the coil pattern221and a sixth end portion222B of the coil pattern222. As described above, the second transmission line22is constituted by the two coil patterns221and222connected in parallel to each other.

In this modification example of the second embodiment, the parallel connection between the two coil patterns221and222suppresses an increase in the electrical resistance of the second transmission line22. As a result, the insertion loss of the transmission line transformer20can be reduced.

Next, another modification example of the second embodiment will be described.

In the second embodiment, the number of turns T of the second transmission line22is twice as many as the number of turns T of the third transmission line23, and accordingly the impedance transformation ratio is increased to about 16. To achieve an impedance transformation ratio of about 16 or more, the number of turns T of the second transmission line22may preferably be twice or more as many as the number of turns T of the third transmission line23. Alternatively, the number of turns T of the first transmission line21, instead of the second transmission line22, may be twice or more as many as the number of turns T of the third transmission line23. In this way, the number of turns T of at least one of the first transmission line21and the second transmission line22may preferably be twice or more as many as the number of turns T of the third transmission line23.

Third Embodiment

A transmission line transformer20according to a third embodiment will be described with reference toFIGS.5A and5B. The same components as those of the transmission line transformer20according to the second embodiment (FIGS.3A and3B) will not be described.

FIG.5Ais a schematic diagram for describing the operation principle of the transmission line transformer20according to the third embodiment. In the second embodiment, the first transmission line21and the third transmission line23have the same number of turns T. In the third embodiment, the number of turns T of the first transmission line21is 2n, whereas the number of turns T of the third transmission line23is n. That is, the number of turns T of the first transmission line21is twice as many as the number of turns T of the third transmission line23.

In this case, the magnitude of the odd-mode current induced in the third transmission line23by the alternating current flowing through the first transmission line21is twice as much as the magnitude of the alternating current flowing through the first transmission line21. The magnitude of the odd-mode current induced in the third transmission line23is four times as much as the magnitude of the alternating current flowing through the series circuit formed of the first transmission line21and the second transmission line22. When the magnitude of the current flowing from the first terminal31into the transmission line transformer20is represented by i, the magnitude of the current flowing through the series circuit formed of the first transmission line21and the second transmission line22is represented by (⅕)i, and the magnitude of the current flowing through the third transmission line23is represented by (⅘)i. The magnitude of the current outputted from the second terminal32is represented by (⅕)i.

Regarding the voltages, 2(0−v1)=v1−v3 holds between the first transmission line21and the third transmission line23. 2(0−v1)=v3−v2 holds between the second transmission line22and the third transmission line23, as in the second embodiment. The solution of the simultaneous equations is v2=5×v1. That is, the voltage v2 at the second terminal32is five times as much as the voltage v1 at the first terminal31.

The impedance seen on the load side from the first terminal31is 1/25 times as much as the impedance of the load connected to the second terminal32. On the other hand, when a load is connected to the first terminal31, the impedance seen on the load side from the second terminal32is 25 times as much as the impedance of the load connected to the first terminal31. In this way, the transmission line transformer20according to the third embodiment functions as an impedance transformation circuit having an impedance transformation ratio of about 25.

FIG.5Bis a schematic perspective view of the transmission line transformer20according to the third embodiment. In the third embodiment, the first transmission line21extends about two rounds along the loop36from the third end portion21A and reaches the fourth end portion21B in plan view. In the first transmission line21, the portion of the second round is disposed inside the portion of the first round. The first transmission line21has substantially the same width as that of the third transmission line23. The center line of the portion of the first round of the first transmission line21is located outside the center line of the third transmission line23, and the center line of the portion of the second round of the first transmission line21is located inside the center line of the third transmission line23. With this arrangement, the first transmission line21has substantially the same width as that of the third transmission line23, and has the number of turns T that is 2.

Next, excellent effects of the third embodiment will be described.

In the third embodiment, the number of turns T of not only the second transmission line22but also the first transmission line21is twice as many as the number of turns T of the third transmission line23, and accordingly the impedance transformation ratio is increased to about 25. Also, in the third embodiment, the first transmission line21, the second transmission line22, and the third transmission line23are disposed so as to overlap each other in plan view, which makes it possible to suppress an increase in the area occupied by the transmission line transformer20in the substrate30. In this way, an impedance transformation circuit with a large impedance transformation ratio can be obtained while suppressing an increase in the size of the circuit.

In the third embodiment, the first transmission line21has a larger width than the second transmission line22. Thus, the first transmission line21has a smaller electrical resistance than the second transmission line22. The impedance at the fifth end portion22A of the second transmission line22is transformed by the transmission line transformer constituted by the first transmission line21and the third transmission line23and becomes larger than the impedance at the third end portion21A of the first transmission line21. Thus, actually, the magnitude (amplitude) of the current flowing through the series circuit formed of the first transmission line21and the second transmission line22gradually decreases from the third end portion21A of the first transmission line21toward the sixth end portion22B of the second transmission line22. That is, the magnitude (amplitude) of the current flowing through the first transmission line21is larger than the magnitude (amplitude) of the current flowing through the second transmission line22. By making the electrical resistance of the first transmission line21, through which a relatively large current flows, lower than the electrical resistance of the second transmission line22, through which a relatively small current flows, the loss resulting from the electrical resistance can be reduced.

Next, a transmission line transformer20according to a modification example of the third embodiment will be described with reference toFIG.6.

FIG.6is a schematic perspective view of the transmission line transformer20according to this modification example of the third embodiment. In this modification example, the first transmission line21is constituted by two coil patterns211and212. The two coil patterns211and212are disposed at different positions in the thickness direction of the substrate30(FIG.1C). In plan view, the coil patterns211and212each have the same shape as that of the first transmission line21according to the third embodiment (FIG.5B) and are each disposed in the same posture as that of the first transmission line21according to the third embodiment.

The positional relationship between the coil pattern212and the third transmission line23is the same as the positional relationship between the first transmission line21and the third transmission line23according to the third embodiment (FIG.5B). The coil pattern211is disposed across the coil pattern212from the third transmission line23.

A via conductor215connects a third end portion211A of the coil pattern211and a third end portion212A of the coil pattern212. A via conductor216connects a fourth end portion211B of the coil pattern211and a fourth end portion212B of the coil pattern212. As described above, the first transmission line21is constituted by the two coil patterns211and212connected in parallel to each other.

The second transmission line22is constituted by the two coil patterns221and222, like the second transmission line22of the transmission line transformer20according to the modification example of the second embodiment illustrated inFIG.4.

Next, excellent effects of this modification example of the third embodiment will be described.

In this modification example of the third embodiment, the first transmission line21is constituted by the two coil patterns211and212connected in parallel to each other, and also the second transmission line22is constituted by the two coil patterns221and222connected in parallel to each other. Thus, the electrical resistances of the first transmission line21and the second transmission line22are decreased. As a result, the insertion loss of the transmission line transformer20can be reduced.

In this modification example, the two coil patterns211and212constituting the first transmission line21have a larger width than the two coil patterns221and222constituting the second transmission line22. Thus, as in the third embodiment, the electrical resistance of the first transmission line21, through which a relatively large current flows, is lower than the electrical resistance of the second transmission line22, through which a relatively small current flows. As a result, the loss resulting from the electrical resistance can be reduced.

Next, another modification example of the third embodiment will be described.

In the third embodiment, the number of turns T of each of the first transmission line21and the second transmission line22is twice as many as the number of turns T of the third transmission line23. Alternatively, the ratio of the number of turns T may be other than 2. By setting the number of turns T of each of the first transmission line21and the second transmission line22to be larger than or equal to the number of turns T of the third transmission line23, an impedance transformation ratio of about 9 or more can be achieved.

Fourth Embodiment

An amplifying circuit according to a fourth embodiment will be described with reference toFIG.7.

FIG.7is an equivalent circuit diagram of the amplifying circuit according to the fourth embodiment. The first terminal31of the transmission line transformer20is connected to an output terminal of an amplifying element40that amplifies a high-frequency signal, with a DC-cut capacitor44interposed therebetween. For example, a heterojunction bipolar transistor may be used as the amplifying element40. The transmission line transformer20used here is the transmission line transformer20according to any one of the first to third embodiments and their modification examples. The high-frequency signal amplified by the amplifying element40is inputted to the transmission line transformer20through the DC-cut capacitor44. The second terminal32of the transmission line transformer20is connected to a DC-cut capacitor45, and the signal outputted from the second terminal32is supplied to a load through the DC-cut capacitor45.

The output terminal of the amplifying element40is grounded through a harmonic termination circuit41. The output terminal of the amplifying element40is also connected to a power supply circuit46with an inductor42interposed therebetween. DC power is supplied from the power supply circuit46to the amplifying element40through the inductor42. The wiring line connecting the power supply circuit46and the inductor42is grounded through a decoupling capacitor43.

Next, excellent effects of the fourth embodiment will be described.

In the fourth embodiment, the transmission line transformer20functions as an impedance matching circuit between the amplifying element40and the load. In the fourth embodiment, the impedance seen on the transmission line transformer20side from the output terminal of the amplifying element40is lower than the impedance seen on the load side from the second terminal32. In the fourth embodiment, the transmission line transformer20according to any one of the first to third embodiments and their modification examples is used as the transmission line transformer20. Thus, an impedance transformation ratio larger than that of a transmission line transformer according to the related art can be achieved, and the size of the impedance matching circuit can be reduced.

Fifth Embodiment

An amplifying circuit according a fifth embodiment will be described with reference toFIG.8. The same components as those of the amplifying circuit according to the fourth embodiment (FIG.7) will not be described.

FIG.8is an equivalent circuit diagram of the amplifying circuit according to the fifth embodiment. In the fourth embodiment, the output terminal of the amplifying element40is connected to the first terminal31of the transmission line transformer20with the DC cut capacitor44(FIG.7) interposed therebetween. In the fifth embodiment, the output terminal of the amplifying element40is directly connected to the first terminal31of the transmission line transformer20. In the fourth embodiment, the output terminal of the amplifying element40is connected to the power supply circuit46with the inductor42(FIG.7) interposed therebetween. In the fifth embodiment, the second end portion23B of the third transmission line23of the transmission line transformer20is connected to the power supply circuit46with the inductor42interposed therebetween. DC power is supplied from the power supply circuit46to the amplifying element40through the inductor42and the third transmission line23.

The power supply circuit46can be regarded as the ground in term of AC. Thus, the second end portion23B of the third transmission line23is AC-grounded through the inductor42. The third transmission line23also serves as a path for supplying DC power.

Next, excellent effects of the fifth embodiment will be described.

In the fifth embodiment, as in the fourth embodiment, an impedance transformation ratio larger than that of a transmission line transformer according to the related art can be achieved, and the size of the impedance matching circuit can be reduced. In the fifth embodiment, the DC-cut capacitor44according to the fourth embodiment (FIG.7) is not necessary.

A modification example of the fifth embodiment will be described. In the fifth embodiment, the second end portion23B of the third transmission line23is connected to the power supply circuit46with the inductor42interposed therebetween. When the third transmission line23has a sufficient inductance, the inductor42is not necessary, and the second end portion23B of the third transmission line23may be directly connected to the power supply circuit46.

Sixth Embodiment

An amplifying circuit according to a sixth embodiment will be described with reference toFIG.9. In the fourth embodiment (FIG.7) and the fifth embodiment (FIG.8), the transmission line transformer20is connected to the output terminal of the amplifying element40. In the sixth embodiment, the transmission line transformer20is connected to an input terminal of the amplifying element40. The transmission line transformer20used here is the transmission line transformer20according to any one of the first to third embodiments and their modification examples.

FIG.9is an equivalent circuit diagram of the amplifying circuit according to the sixth embodiment. A high-frequency signal is inputted from a high-frequency signal input terminal50to the second terminal32of the transmission line transformer20through a DC-cut capacitor47. The first terminal31of the transmission line transformer20is connected to the input terminal of the amplifying element40with a DC-cut capacitor48interposed therebetween. The transmission line transformer20functions as an impedance matching circuit on the input side of the amplifying element40. In the sixth embodiment, the impedance seen on the transmission line transformer20side from the high-frequency signal input terminal50is higher than the impedance seen on the amplifying element40side from the first terminal31. In this way, impedance transformation for decreasing the impedance is performed in the sixth embodiment.

Next, excellent effects of the sixth embodiment will be described.

In the sixth embodiment, as in the fourth and fifth embodiments, an impedance transformation ratio larger than that of a transmission line transformer according to the related art can be achieved, and the size of the impedance matching circuit can be reduced.

Seventh Embodiment

An amplifying circuit according to a seventh embodiment will be described with reference toFIG.10. In the seventh embodiment, amplifying elements40are connected in multiple stages to form a multi-stage power amplifying circuit.

FIG.10is a block diagram of the amplifying circuit according to the seventh embodiment. A plurality of amplifying elements40are connected in multiple stages between the high-frequency signal input terminal50and a high-frequency signal output terminal51from which an amplified high-frequency signal is outputted. An input-side transmission line transformer20is disposed between the high-frequency signal input terminal50and a first-stage amplifying element40. An output-side transmission line transformer20is disposed between a last-stage amplifying element40and the high-frequency signal output terminal51. An interstage transmission line transformer20is disposed between one amplifying element40and the subsequent amplifying element40. As each of the input-side transmission line transformer20, the output-side transmission line transformer20, and the interstage transmission line transformer20, the transmission line transformer20according to any one of the first to third embodiments and their modification examples is used.

DC power is supplied to the plurality of amplifying elements40from the power supply circuit46through the inductors42. DC bias is supplied to the plurality of amplifying elements40from bias control circuits53.

Next, excellent effects of the seventh embodiment will be described.

In the seventh embodiment, the transmission line transformers20function as input-side, interstage, and output-side impedance matching circuits. In the seventh embodiment, the sizes of the impedance matching circuits can be reduced as in the fourth embodiment (FIG.7), the fifth embodiment (FIG.8), and the sixth embodiment (FIG.9).

A modification example of the seventh embodiment will be described.

In the seventh embodiment, the transmission line transformer20according to any one of the first to third embodiments and their modification examples is used as each of the input-side, output-side, and interstage impedance matching circuits. At a part where a large impedance transformation ratio is not necessary, the transmission line transformer20according to any one of the first to third embodiments and their modification examples is not necessary. For example, a transmission line transformer that does not include the second transmission line22inFIG.1Abut includes the first transmission line21and the third transmission line23inFIG.1Amay be used as an impedance matching circuit. Alternatively, a ladder impedance matching circuit formed of a capacitance and an inductance may be used. For example, the transmission line transformer20according to any one of the first to third embodiments and their modification examples may be used as at least one of the input-side, output-side, and interstage impedance matching circuits.

Eighth Embodiment

Simulation results of input/output impedances of impedance transformation circuits according to an eighth embodiment will be described with reference toFIGS.11A to13B.

FIGS.11A and11Bare block diagrams of the impedance transformation circuits according to the eighth embodiment as simulation targets. As the impedance transformation circuits, the transmission line transformer20according to the second embodiment (FIGS.3A and3B) having an impedance transformation ratio of about 16 is used.

In the impedance transformation circuit illustrated inFIG.11A, an AC power supply55having an output impedance of about 3Ω is connected to the first terminal31of the transmission line transformer20, and the second terminal32is terminated with about 50Ω. In the impedance transformation circuit illustrated inFIG.11B, the AC power supply55having an output impedance of about 50Ω is connected to the second terminal32of the transmission line transformer20, and the first terminal31was terminated with about 3Ω.

In the impedance transformation circuit illustrated inFIG.11A, the impedance seen on the transmission line transformer20side from the first terminal31is represented by Z1. In the impedance transformation circuit illustrated in FIG.11B, the impedance seen on the transmission line transformer20side from the second terminal32is represented by Z2. An electromagnetic-field simulation is performed with the frequency being changed from about 100 MHz to about 20 GHz, thereby obtaining the impedances Z1 and Z2. The transmission line transformer20is designed to achieve an impedance transformation ratio of about 16 in the frequency band ranging from about 2.3 GHz to about 2.69 GHz.

FIG.12Ais a graph obtained by plotting the trajectory of the impedance Z1 at various frequencies on a Smith chart. A reference impedance Zref at the reference point (center point) of the Smith chart is about 3Ω. The impedance Z1 in the frequency band ranging from about 2.3 GHz to about 2.69 GHz, the impedance Z1 in the frequency band of the second harmonic (ranging from about 4.6 GHz to about 5.38 GHz), and the impedance Z1 in the frequency band of the third harmonic (ranging from about 6.9 GHz to about 8.07 GHz) are represented by the bold lines. It can be seen that the impedance Z1 is near the reference point of the Smith chart and is approximately 3Ω in the frequency band ranging from about 2.3 GHz to about 2.69 GHz. As a result, it is confirmed that the impedance is transformed from about 50Ω to about 1/16, that is, about 3Ω.

FIG.12Bis a graph obtained by plotting the trajectory of the impedance Z2 at various frequencies on a Smith chart. A reference impedance Zref at the reference point (center point) of the Smith chart is about 50Ω. The impedance Z2 in the frequency band ranging from about 2.3 GHz to about 2.69 GHz, the impedance Z2 in the frequency band of the second harmonic (ranging from about 4.6 GHz to about 5.38 GHz), and the impedance Z2 in the frequency band of the third harmonic (ranging from about 6.9 GHz to about 8.07 GHz) are represented by bold lines. It can be seen that the impedance Z2 is near the reference point of the Smith chart and is approximately 50Ω in the frequency band ranging from about 2.3 GHz to about 2.69 GHz. As a result, it is confirmed that the impedance is transformed from about 3Ω to about 16 times, that is, about 50Ω.

FIGS.13A and13Bare graphs illustrating simulation results of insertion loss of the transmission line transformer20. The horizontal axis represents frequency in “GHz”, and the vertical axis represents insertion loss in “dB”. An insertion loss IL is defined by the following equation.

IL=10⁢log⁢S2121-S112
Here, S11and S21are scattering parameters. A smaller absolute value on the vertical axis represents a smaller loss.FIG.13Bis an enlarged view of the range of frequencies 1 GHz to 6 GHz on the horizontal axis ofFIG.13A. It can be seen that the insertion loss is small in the frequency band ranging from about 2.3 GHz to about 2.69 GHz.

From the simulations in the eighth embodiment, it is confirmed that an impedance matching circuit having an impedance transformation ratio of about 16 can be obtained by using the transmission line transformer20according to the second embodiment. Also, it is confirmed that an impedance matching circuit with low insertion loss can be obtained by using the transmission line transformer20according to the second embodiment. These simulation results also show that an impedance matching circuit with low insertion loss can be obtained by using the transmission line transformer20according to the first embodiment or the third embodiment.

Ninth Embodiment

Simulation results of input/output impedances of impedance transformation circuits according to a ninth embodiment will be described with reference toFIGS.14A to16B.

FIGS.14A and14Bare block diagrams of the impedance transformation circuits as simulation targets. The impedance transformation circuit illustrated inFIG.14Ais formed by connecting the harmonic termination circuit41between the AC power supply55and the transmission line transformer20illustrated inFIG.11A. The impedance transformation circuit illustrated inFIG.14Bis formed by connecting the harmonic termination circuit41between the load and the transmission line transformer20illustrated inFIG.11B.

InFIG.14A, the impedance seen on the harmonic termination circuit41and the transmission line transformer20side from the AC power supply55is represented by Z1. In FIG.14B, the impedance seen on the harmonic termination circuit41and the transmission line transformer20side from the AC power supply55is represented by Z2. An electromagnetic-field simulation is performed with the frequency being changed from about 100 MHz to about 20 GHz, thereby obtaining the impedances Z1 and Z2.

FIG.15Ais a graph obtained by plotting the trajectory of the impedance Z1 at various frequencies on a Smith chart. A reference impedance Zref at the reference point (center point) of the Smith chart is about 3Ω. The impedance Z1 in the frequency band ranging from about 2.3 GHz to about 2.69 GHz, the impedance Z1 in the frequency band of the second harmonic (ranging from about 4.6 GHz to about 5.38 GHz), and the impedance Z1 in the frequency band of the third harmonic (ranging from about 6.9 GHz to about 8.07 GHz) are represented by bold lines. As in the eighth embodiment (FIG.12A), it can be seen that the impedance Z1 is near the reference point of the Smith chart and is approximately 3Ω in the frequency band ranging from about 2.3 GHz to about 2.69 GHz. As a result, it is confirmed that the impedance is transformed from about 50Ω to about 1/16, that is, about 3Ω.

FIG.15Bis a graph obtained by plotting the trajectory of the impedance Z2 at various frequencies on a Smith chart. A reference impedance Zref at the reference point (center point) of the Smith chart is about 50Ω. The impedance Z2 in the frequency band ranging from about 2.3 GHz to about 2.69 GHz, the impedance Z2 in the frequency band of the second harmonic (ranging from about 4.6 GHz to about 5.38 GHz), and the impedance Z2 in the frequency band of the third harmonic (ranging from about 6.9 GHz to about 8.07 GHz) are represented by bold lines. It can be seen that the impedance Z2 is near the reference point of the Smith chart and is approximately 50Ω in the frequency band ranging from about 2.3 GHz to about 2.69 GHz. As a result, it is confirmed that the impedance is transformed from about 3Ω to about 16 times, that is, about 50Ω.

FIGS.16A and16Bare graphs illustrating simulation results of insertion loss of the transmission line transformer20. The horizontal axis represents frequency in “GHz”, and the vertical axis represents insertion loss in “dB”. A smaller absolute value on the vertical axis represents a smaller loss.FIG.16Bis an enlarged view of the range of frequencies 1 GHz to 6 GHz on the horizontal axis ofFIG.16A. It can be seen that the insertion loss is small in the frequency band ranging from about 2.3 GHz to about 2.69 GHz.

From the simulations in the ninth embodiment, it is confirmed that an impedance matching circuit with low insertion loss can be obtained by using the transmission line transformer20according to the second embodiment, also in the configuration including the harmonic termination circuit41. The comparison betweenFIG.12AandFIG.15Ashows that the harmonic termination circuit41causes a decrease in the impedance Z1 for the second harmonic and the third harmonic. Thus, the transmission line transformer20according to the second embodiment, which is a simulation target, can be used also as an output matching circuit for realizing the operation of a switching mode power amplifier. Accordingly, the power-added efficiency of the switching mode power amplifier is improved.

In addition, it can be easily understood, from these simulation results, that an impedance matching circuit with low insertion loss can be obtained by using the transmission line transformer20according to the first embodiment or the third embodiment.

Tenth Embodiment

An amplifying circuit according to a tenth embodiment will be described with reference toFIGS.17,18, and19. The same components as those of the amplifying circuit according to the fourth embodiment (FIG.7) will not be described.

FIG.17is an equivalent circuit diagram of the amplifying circuit according to the tenth embodiment. The amplifying circuit according to the tenth embodiment includes two amplifying systems60A and60B. The two amplifying systems60A and60B each include the amplifying element40and the transmission line transformer20. In each of the two amplifying systems60A and60B, the configuration from the amplifying element40to the second terminal32is the same as the configuration from the amplifying element40to the second terminal32of the amplifying circuit according to the fourth embodiment (FIG.7). The second terminals32of the two amplifying systems60A and60B are connected to each other and are connected to one electrode of the single DC-cut capacitor45. The other electrode of the DC-cut capacitor45is connected to an output terminal37. A resistance element61and a capacitor62are connected in parallel to each other between the output terminal of the amplifying element40of the amplifying system60A and the output terminal of the amplifying element40of the amplifying system60B. A connection circuit formed of the resistance element61and the capacitor62is referred to as an inter-system phase-shift circuit65.

The operation of the amplifying circuit according to the tenth embodiment will be described. The amplifying circuit according to the tenth embodiment constitutes a Webb's power combiner.

High-frequency signals having substantially the same phase and substantially the same amplitude are inputted to the two amplifying elements40. The two amplifying elements40amplify the input high-frequency signals and output high-frequency signals having substantially the same phase and substantially the same amplitude. The high-frequency signals amplified by the two amplifying elements40are subjected to impedance transformation performed by the two transmission line transformers20and are then outputted from the second terminals32. The high-frequency signals outputted from the second terminals32are combined before the DC-cut capacitor45and the resulting signal is outputted from the output terminal37.

The function of the inter-system phase-shift circuit65that connects the two amplifying systems60A and60B will be described. A current path extending from the output terminal of the amplifying element40of the amplifying system60A to the output terminal of the amplifying element40of the amplifying system60B includes a first signal path63passing through the transmission line transformers20and a second signal path64passing through the inter-system phase-shift circuit65. The first signal path63and the second signal path64are configured such that the difference between the amount of phase change in the high-frequency signal transmitted through the first signal path63and the amount of phase change in the high-frequency signal transmitted through the second signal path64from the output terminal of the amplifying element40of the amplifying system60A to the output terminal of the amplifying element40of the amplifying system60B is about 180 degrees. For example, the amount of phase change in the case of passing through the first signal path63is about +90 degrees, whereas the amount of phase change in the case of passing through the second signal path64is about −90 degrees.

The two high-frequency signals that are outputted from the amplifying element40of the amplifying system60B, that are transmitted through the first signal path63and the second signal path64, and that reach the output terminal of the amplifying element40of the amplifying system60B have a phase difference of about 180 degrees, and thus power offset occurs. That is, the high-frequency signal outputted from the amplifying element40of the amplifying system60A hardly appears at the output terminal of the amplifying element40of the amplifying system60B. Similarly, the high-frequency signal outputted from the amplifying element40of the amplifying system60B hardly appears at the output terminal of the amplifying element40of the amplifying system60A. Thus, high-frequency isolation is secured between the output terminals of the two amplifying elements40of the two amplifying systems60A and60B. As a result, almost all the power of the high-frequency signals outputted from the two amplifying elements40can be transmitted to the output terminal37.

FIG.18is a plan view illustrating a plurality of conductor patterns disposed in a first conductor layer of the amplifying circuit according to the tenth embodiment. InFIG.18, the conductor patterns are hatched. The conductor patterns in the first layer include the first transmission lines21and parts of the inductors42of the two amplifying systems60A and60B, and lands81,82,85, and86for mounting surface mount devices. Each first transmission line21is constituted by a conductor pattern whose number of turns T is 1. Furthermore, lands83and84common to the two amplifying systems60A and60B are disposed in the first conductor layer.

The conductor patterns constituting the parts of the two inductors42are connected to the respective lands81. The output terminals of the amplifying elements40and one terminals of the DC-cut capacitors44are connected to the lands81. Furthermore, the resistance element61and the capacitor62are connected between the two lands81. One end portions of the conductor patterns of the first transmission lines21are connected to the lands82. The other terminals of the DC-cut capacitors44are connected to the lands82. The decoupling capacitors43are connected between the lands85and the lands86.

The plurality of conductor patterns constituting the amplifying system60A and the plurality of conductor patterns constituting the amplifying system60B are axisymmetric in plan view. A grounded conductor pattern71is disposed along the symmetry axis between the plurality of conductor patterns constituting the amplifying system60A and the plurality of conductor patterns constituting the amplifying system60B. Furthermore, the land83and the land84are disposed on the symmetry axis. The DC-cut capacitor45is connected between the land83and the land84.

FIG.19is an exploded perspective view of a plurality of conductor layers provided in the substrate30used for the amplifying circuit according to the tenth embodiment. Conductor layers91to98as first to eighth layers are disposed in order in the thickness direction from a mount surface on which circuit components are mounted. InFIG.19, the conductor patterns in the odd-numbered conductor layers91,93,95, and97are given hatching with a relatively high density, and the conductor patterns in the even-numbered conductor layers92,94,96, and98are given hatching with a relatively low density.

The plurality of conductor patterns disposed in the conductor layer91as the first layer are as illustrated inFIG.18. InFIG.19, a symbol formed of a solid circle and line segments extending upward and downward is given at the position where via conductors connected to both a conductor pattern in an upper layer and a conductor pattern in a lower layer are connected. A symbol formed of a solid circle and a line segment extending downward is given at the position where only a via conductor connected to a conductor pattern in a lower layer is connected. A symbol formed of a hollow circle and a line segment extending upward is given at the position where only a via conductor connected to a conductor pattern in an upper layer is connected.

The grounded conductor pattern71is disposed in each of the conductor layers92to97as the second to seventh layers. The grounded conductor patterns71in the individual conductor layers substantially overlap each other in plan view. The grounded conductor patterns71adjacent to each other in the vertical direction are connected to each other by four via conductors.

In the conductor layer98as the eighth layer, a ground plane70and a power supply wiring line72are disposed. The grounded conductor pattern71in the seventh layer is connected to the ground plane70by the four via conductors. In this way, all the grounded conductor patterns71in the first to seventh layers are grounded. The power supply wiring line72is connected to the power supply circuit46(FIG.17).

The plurality of conductor patterns constituting the two inductors42are disposed in the conductor layers91to94as the first to fourth layers such that two conductor patterns are disposed in each layer. The number of turns T of each conductor pattern in each conductor layer is 1. In each inductor42, the termination portion of the conductor pattern in the fourth layer constituting the inductor42is connected to the land86in the first layer, with a plurality of via conductors and the conductor patterns in the third and second layers interposed therebetween. Furthermore, in each inductor42, the termination portion of the conductor pattern in the fourth layer constituting the inductor42is connected to a power supply wiring line76in the seventh layer, with the conductor patterns in the fifth and sixth layers and a plurality of via conductors interposed therebetween. The power supply wiring line76in the seventh layer is connected to the power supply wiring line72in the eighth layer with a plurality of via conductors interposed therebetween.

The lands85in the first layer are connected to the ground plane70, with a plurality of via conductors and the conductor patterns in the second to seventh layers interposed therebetween.

The two third transmission lines23are disposed in the conductor layer92as the second layer. Each of the third transmission lines23is constituted by a conductor pattern whose number of turns T is 1. In each third transmission line23, one end portion is connected to the grounded conductor pattern71in the same conductor layer, whereas the other end portion is connected to the land82-side end portion of the first transmission line21, with a via conductor interposed therebetween.

The two second transmission lines22are disposed in the conductor layer93as the third layer. Each of the second transmission lines22is constituted by a substantially spiral conductor pattern whose number of turns T is 2. In each second transmission line22, the inner end portion is connected to one end portion of the first transmission line21, with a plurality of via conductors and the conductor pattern in the second layer interposed therebetween. In each second transmission line22, the outer end portion is connected to a conductor pattern75in the fourth layer, with a via conductor interposed therebetween. The conductor pattern75is connected to the land83in the first layer, with a plurality of via conductors and the conductor patterns in the second and third layers interposed therebetween.

In each of the conductor layers92to96as the second to sixth layers, the conductor patterns belonging to the amplifying system60A and the conductor patterns belonging to the amplifying system60B are axisymmetric, like the conductor patterns in the conductor layer91as the first layer.

Next, excellent effects of the tenth embodiment will be described.

In the tenth embodiment, the powers of high-frequency signals outputted from the two amplifying elements40are combined, thereby obtaining output power that is about twice (i.e., +3 dB) as much as the power in the case of using a single amplifying element40. Furthermore, as in the first embodiment, the size of the amplifying circuit can be reduced compared to the configuration of achieving a large impedance transformation ratio by cascade-connecting a plurality of transmission line transformers each having a small impedance transformation ratio. In addition, the number of components can be reduced compared to the case where the impedance transformation circuit is constituted by a plurality of surface mount devices including a capacitor and an inductor. Furthermore, the degradation in characteristics of the amplifying circuit resulting from the variations in characteristics of individual surface mount devices can be suppressed.

The conductor patterns of the amplifying system60A and the conductor patterns of the amplifying system60B are axisymmetric, and thus a phase shift of high-frequency signals at the second terminals32(FIG.17) serving as power combining terminals can be suppressed, and the accuracy of phase matching can be increased.

Furthermore, the grounded conductor pattern71is disposed between the conductor patterns of the amplifying system60A and the conductor patterns of the amplifying system60B. Thus, the leakage of the power from one of the amplifying systems60A and60B to the other can be reduced. As a result, the loss caused by leakage of power can be reduced.

Eleventh Embodiment

An amplifying circuit according to an eleventh embodiment will be described with reference toFIG.20. The same components as those of the amplifying circuit according to the tenth embodiment (FIGS.17,18, and19) will not be described.

FIG.20is an equivalent circuit diagram of the amplifying circuit according to the eleventh embodiment. In the tenth embodiment, the configuration from the amplifying element40to the second terminal32in each of the two amplifying systems60A and60B (FIG.17) is the same as the configuration from the amplifying element40to the second terminal32of the amplifying circuit according to the fourth embodiment (FIG.7). In contrast, in the eleventh embodiment, the configuration from the amplifying element40to the second terminal32in each of the two amplifying systems60A and60B is the same as the configuration from the amplifying element40to the second terminal32of the amplifying circuit according to the fifth embodiment (FIG.8).

Next, excellent effects of the eleventh embodiment will be described.

In the eleventh embodiment, as in the tenth embodiment, output power about twice as much as the power in the case of using a single amplifying element40can be obtained. Furthermore, the degradation in characteristics of the amplifying circuit resulting from the variations in characteristics of individual surface mount devices can be suppressed. Furthermore, as in the fifth embodiment, the DC-cut capacitors44according to the tenth embodiment (FIG.17) are not necessary.

The above-described embodiments are examples, and configurations according to different embodiments can be partially replaced or combined. Similar functions and effects of similar configurations according to a plurality of embodiments are not mentioned for each embodiment. The present disclosure is not limited to the above-described embodiments. It would be obvious to those skilled in the art that various changes, improvements, combinations, and the like can be made.