DOHERTY AMPLIFIER

A Doherty amplifier includes a distributor, a first amplifier, a second amplifier, a third node, an impedance conversion circuit having a first end connected to a first node and a second end connected to the third node, and rotating an impedance viewed from the first amplifier to the third node with respect to an impedance viewed from the first amplifier to the first node within a range of 360°±45° on a Smith chart in a second harmonic wave, and a harmonic tuning circuit having a third end connected to a line connecting the first amplifier and the third node at the first node, and making an absolute value of an impedance with respect to a reference potential at the third end in the second harmonic wave smaller than an absolute value of an impedance with respect to the reference potential at the third end in the fundamental wave.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority based on Japanese Patent Application No. 2022-096711 filed on Jun. 15, 2022, and the entire contents of the Japanese patent applications are incorporated herein by reference.

FIELD

The present disclosure relates to a Doherty amplifier.

BACKGROUND

A Doherty amplifier is known as an amplifier for amplifying high frequency signals such as microwaves. In the Doherty amplifier, a main amplifier and a peak amplifier amplify input signals in parallel, and the amplified signals are combined at a combining node. It is known that a harmonic tuning circuit for processing a harmonic component is provided in any one of a line between the main amplifier and the combining node and another line between the peak amplifier and the combining node (for example, Patent Document 1: Japanese Patent Application Laid-Open No. 2018-74320).

SUMMARY

A Doherty amplifier according to the present disclosure includes: a distributor that distributes an input signal inputted to an input terminal into two signals; a first amplifier that amplifies one of the two signals and outputs a first amplified signal to a first node; a second amplifier that amplifies the other of the two signals and outputs a second amplified signal to a second node; a third node that combines the first amplified signal output from the first amplifier and the second amplified signal output from the second amplifier and outputs a combined signal to an output terminal; an impedance conversion circuit that has a first end connected to the first node and a second end connected to the third node, and rotates an impedance viewed from the first amplifier to the third node with respect to an impedance viewed from the first amplifier to the first node within a range of 360°±45° on a Smith chart in a second harmonic wave, the second harmonic wave having a twice as high as a frequency of a fundamental wave that is a signal having a center frequency of an operation band; and a harmonic tuning circuit that has a third end connected to a line connecting the first amplifier and the third node at the first node, and makes an absolute value of an impedance with respect to a reference potential at the third end in the second harmonic wave smaller than an absolute value of an impedance with respect to the reference potential at the third end in the fundamental wave.

A Doherty amplifier according to the present disclosure includes: a distributor that distributes an input signal inputted to an input terminal into two signals; a first amplifier that amplifies one of the two signals and outputs a first amplified signal to a first node; a second amplifier that amplifies the other of the two signals and outputs a second amplified signal to a second node; a third node that combines the first amplified signal output from the first amplifier and the second amplified signal output from the second amplifier and outputs a combined signal to an output terminal; an impedance conversion circuit that has a first end connected to the first node and a second end connected to the third node, and rotates an impedance viewed from the first amplifier to the third node with respect to an impedance viewed from the first amplifier to the first node within a range of 360°±45° on a Smith chart in a second harmonic wave, the second harmonic wave having a twice as high as a frequency of a fundamental wave that is a signal having a center frequency of an operation band; and a harmonic tuning circuit that has a third end connected to a fourth node positioned on any one of the third node, a first line connecting the first amplifier and the third node, a second line connecting the second amplifier and the third node, and a third line connecting the third node and the output terminal, and makes an absolute value of an impedance with respect to a reference potential at the third end in the second harmonic wave smaller than an absolute value of an impedance with respect to the reference potential at the third end in the fundamental wave; wherein an electrical length between the third node and the fourth node is 1/16 or less of the wavelength of the fundamental wave.

DETAILED DESCRIPTION OF EMBODIMENTS

InFIGS.8and9of Patent Document 1, for example, a first terminal of one harmonic tuning circuit is connected to a node in a line between a main amplifier or a peak amplifier and a combining node. Patent Document 1 does not describe the length of the line between the node connecting the harmonic tuning circuit and the combining node. The Doherty amplifier can be miniaturized by using only one harmonic tuning circuit. However, if one harmonic tuning circuit does not appropriately process a harmonic wave output from the main amplifier and a harmonic wave output from the peak amplifier, the characteristic of the Doherty amplifier deteriorates.

The present disclosure has been made in view of the above problems, and an object of the present disclosure is to improve the characteristic of the Doherty amplifier.

Details of Embodiments of the Present Disclosure

First, the contents of the embodiments of this disclosure are listed and explained.

(1) A Doherty amplifier according to the present disclosure includes: a distributor that distributes an input signal inputted to an input terminal into two signals; a first amplifier that amplifies one of the two signals and outputs a first amplified signal to a first node; a second amplifier that amplifies the other of the two signals and outputs a second amplified signal to a second node; a third node that combines the first amplified signal output from the first amplifier and the second amplified signal output from the second amplifier and outputs a combined signal to an output terminal; an impedance conversion circuit that has a first end connected to the first node and a second end connected to the third node, and rotates an impedance viewed from the first amplifier to the third node with respect to an impedance viewed from the first amplifier to the first node within a range of 360°±45° on a Smith chart in a second harmonic wave, the second harmonic wave having a twice as high as a frequency of a fundamental wave that is a signal having a center frequency of an operation band; and a harmonic tuning circuit that has a third end connected to a line connecting the first amplifier and the third node at the first node, and makes an absolute value of an impedance with respect to a reference potential at the third end in the second harmonic wave smaller than an absolute value of an impedance with respect to the reference potential at the third end in the fundamental wave.

(2) A Doherty amplifier according to the present disclosure includes: a distributor that distributes an input signal inputted to an input terminal into two signals; a first amplifier that amplifies one of the two signals and outputs a first amplified signal to a first node; a second amplifier that amplifies the other of the two signals and outputs a second amplified signal to a second node; a third node that combines the first amplified signal output from the first amplifier and the second amplified signal output from the second amplifier and outputs a combined signal to an output terminal; an impedance conversion circuit that has a first end connected to the first node and a second end connected to the third node, and rotates an impedance viewed from the first amplifier to the third node with respect to an impedance viewed from the first amplifier to the first node within a range of 360°±45° on a Smith chart in a second harmonic wave, the second harmonic wave having a twice as high as a frequency of a fundamental wave that is a signal having a center frequency of an operation band; and a harmonic tuning circuit that has a third end connected to a fourth node positioned on any one of the third node, a first line connecting the first amplifier and the third node, a second line connecting the second amplifier and the third node, and a third line connecting the third node and the output terminal, and makes an absolute value of an impedance with respect to a reference potential at the third end in the second harmonic wave smaller than an absolute value of an impedance with respect to the reference potential at the third end in the fundamental wave; wherein an electrical length between the third node and the fourth node is 1/16 or less of the wavelength of the fundamental wave.

(3) In the above (1) or (2), the harmonic tuning circuit may short-circuit between the third end and the reference potential in the second harmonic wave and may not short-circuit between the third end and the reference potential in the fundamental wave.

(4) In the above (1) or (2), the harmonic tuning circuit may open between the third end and the reference potential in the fundamental wave.

(5) In any one of (1) to (4) above, the harmonic tuning circuit may be a stub having an electric length of 3/16 or more and 5/16 or less of the wavelength of the fundamental wave, and a fourth end connected to the reference potential.

(6) In any one of (1) to (4) above, the harmonic tuning circuit may be a stub having an electrical length of 1/16 or more and 3/16 or less of the wavelength of the fundamental wave, and a fourth end being opened.

(7) In any one of (1) to (6) above, the impedance conversion circuit may rotate an impedance viewed from the first amplifier to the third node with respect to an impedance viewed from the first amplifier to the first node within a range of 180°±22.5° on a Smith chart in the fundamental wave.

(8) In any one of (1) to (6) above, the impedance conversion circuit may be a transmission line having an electric length of 3/16 or more and 5/16 or less of the fundamental wave.

(9) In any one of (1) to (8) above, the Doherty amplifier circuit may include no harmonic tuning circuit in which the third end is connected to a line connecting the second amplifier and the third node, and which makes the absolute value of the impedance with respect to the reference potential at the third end in the second harmonic wave smaller than the absolute value of the impedance with respect to the reference potential at the third end in the fundamental wave.

(10) In any one of (1) to (9) above, the first amplifier may be a main amplifier and the second amplifier may be a peak amplifier.

(11) In any one of (1) to (9) above, the first amplifier may be a peak amplifier and the second amplifier may be a main amplifier.

Specific examples of the Doherty amplifier in accordance with embodiments of the present disclosure are described below with reference to the drawings. The present disclosure is not limited to these examples, but is indicated by the claims, which are intended to include all modifications within the meaning and scope of the claims.

First Embodiment

A first embodiment and a first variation are examples of a forward Doherty amplifier having an impedance conversion circuit between a main amplifier and a combining node.FIG.1is a block diagram of the Doherty amplifier according to the first embodiment. As illustrated inFIG.1, in a Doherty amplifier100of the first embodiment, a main amplifier10and a peak amplifier20are connected in parallel between an input terminal Tin and an output terminal Tout. A high frequency signal is input to the input terminal Tin as an input signal. A distributor30distributes an input signal inputted to the input terminal Tin into two signals. The distributor30is, for example, a Wilkinson distributor.

One of the distributed signals is input to the main amplifier10. The main amplifier amplifies one of the distributed signals and outputs the amplified signal to a node N1. In the main amplifier10, the input signal is input to an amplifying element12through a matching circuit14and a harmonic tuning circuit16. The matching circuit14matches an impedance viewed from the distributor30to the matching circuit14with an impedance viewed from the matching circuit14to the amplifying element12. The harmonic tuning circuit16is, for example, a filter for passing a fundamental wave included in the input signal and suppressing a harmonic signal. The harmonic tuning circuit16may not be provided. The amplifying element12amplifies the input signal and outputs the amplified signal to the node N1via a matching circuit18. The matching circuit18matches an impedance viewed from the amplifying element12to the matching circuit18with an impedance viewed from the matching circuit18to the node N1. A signal output from the main amplifier10to the node N1is output to a node N3via an impedance conversion circuit34(Z conversion circuit).

The other signal distributed by the distributor30is input to the peak amplifier20via a phase adjustment circuit32. The phase adjustment circuit32adjusts a phase difference between the main amplifier10and the peak amplifier20. The peak amplifier20amplifies the other signal and outputs the amplified signal to a node N2. In the peak amplifier20, the input signal is input to an amplifying element22via a matching circuit24and a harmonic tuning circuit26. The matching circuit24matches an impedance viewed from the distributor30to the matching circuit24with an impedance viewed from the matching circuit24to the amplifying element22. The harmonic tuning circuit26is, for example, a filter for passing a fundamental wave included in an input signal and suppressing a harmonic signal. The harmonic tuning circuit26may not be provided. The amplifying element22amplifies the input signal and outputs the amplified signal to the node N2via a matching circuit28. The matching circuit28matches an impedance viewed from the amplifying element22to the matching circuit28with an impedance viewed from the matching circuit28to the node N2. The signal output from the peak amplifier to the node N2is output to the node N3.

The node N3(third node), which is the combining node, combines the signal output from the main amplifier10and the signal output from the peak amplifier20, and outputs the combined signal to the output terminal Tout. An impedance conversion circuit36(Z conversion circuit) converts an impedance viewed from the node N3to the impedance conversion circuit36to an impedance viewed from the impedance conversion circuit36to the output terminal Tout.

The amplifying elements12and22are, for example, FETs (Field Effect Transistors), and their sources are grounded, high frequency signals are input to gates of the FETs, and signals are output from drains of the FETs. Each of the FETs is, for example, a GaNFET or an LDMOS (Laterally Diffused Metal Oxide Semiconductor). Each of the amplifying elements12and22may be provided with a multi-stage FET. Bias circuits for supplying bias voltages to the amplifying elements12and22are omitted.

The amplifying element12performs class AB or class B operation, and the amplifying element22performs class C operation. When the input power is small, the amplifying element12mainly amplifies the input signal. When the input power becomes large, the amplifying element22amplifies the peak of the input signal in addition to the amplification of the input signal by the amplifying element12. Thus, the amplifying elements12and22amplify the input signals. When the input power is small and the amplifying element22is off, the impedance viewed from the main amplifier10to the node N3is twice (for example, 100Ω) of a load R of the output terminal Tout. When the input power becomes large and the amplifying element22operates, the impedance from the main amplifier10to the node N3and the impedance from the peak amplifier20to the node N3are the load R (for example, 50Ω) of the output terminal Tout. The matching circuit18is adjusted so that the amplifying element12operates optimally at a saturated output power (for example, the efficiency is maximized) in the load2R when the amplifying element22is off, and so that the amplifying element12operates optimally at the saturated output power (for example, the efficiency is maximized) in the load R when the amplifying element22operates. The matching circuit28is adjusted so that the impedance viewed from the node N3to the amplifying element22is open when the amplifying element22is off, while the matching circuit28is adjusted so that the amplifying element22operates optimally at the saturated output power in the load R when the amplifying element22operates.

The fundamental wave is a signal at the center frequency of the operating band of the Doherty amplifier100(i.e., the frequency band at which the Doherty amplifier can obtain a desired amplification characteristic). A second harmonic wave is a signal having twice the frequency of the fundamental wave. The amplifying elements12and22amplify the fundamental wave but generate the second harmonic waves. When the second harmonic wave output from the output terminal Tout is large, energy is output as the second harmonic wave, so that efficiency in the fundamental wave is reduced. A harmonic tuning circuit40is provided in order to improve the characteristics of the Doherty amplifier100by processing the harmonic wave so that the second harmonic wave is not outputted from the outputting terminal Tout.

A first end of the harmonic tuning circuit40is connected to the node N1. When a node to which the harmonic tuning circuit40is connected to the signal line is referred to as a node N4, the nodes N1and N4coincide with each other. The harmonic tuning circuit40short-circuits the nodes N1and N4with respect to a reference potential such as ground for the second harmonic wave, and does not short-circuits the nodes N1and N4with respect to the reference potential for the fundamental wave and makes the nodes N1and N4in a state close to open, for example. When the nodes N1and N4and the reference potential are short-circuited, an absolute value of an impedance between the nodes N1and N4and the reference potential is substantially 0. When nodes N1and N4and the reference potential are opened, the absolute value of the impedance between nodes N1and N4and the reference potential is almost infinite.

FIG.2is a Smith chart of the impedance at the nodes N1and N3in the first embodiment. The impedance is an impedance viewed from the main amplifier10to the node N1or N3. Due to the harmonic tuning circuit40, the impedance of the second harmonic wave at the node N1is short-circuited, and is at a short-circuit position60inFIG.2. Thus, the second harmonic wave output from the main amplifier10is mostly reflected at the node N1.

The impedance conversion circuit34rotates the impedance viewed from the matching circuit18to the node N1by 360° in the clockwise direction around a reference impedance66as indicated by an arrow62on the Smith chart ofFIG.2to convert it into the impedance viewed from the impedance conversion circuit34to the node N3. As a result, the impedance viewed from the matching circuit18to the node N3and the impedance viewed from the impedance conversion circuit34to the node N1are at substantially the same position on the Smith chart. Therefore, the impedance of the second harmonic wave at the node N3is short-circuited, and is at the short-circuit position60inFIG.2. Thus, the second harmonic wave output from the peak amplifier20is mostly reflected at the node N3.

On the other hand, in the fundamental wave, the load impedance viewed from the amplifying element12to the matching circuit18is set so that the amplifying element12operates optimally as described above. The matching circuit18converts the load impedance having an imaginary component viewed from the amplifying element12to the matching circuit18into the impedance seen from the matching circuit18to the node N1. The impedance seen from the matching circuit18to the node N1is located on a substantially real axis64ofFIG.2. The harmonic tuning circuit40makes the node N1substantially open with respect to the reference potential in the fundamental wave. Therefore, the harmonic tuning circuit40hardly affects the impedance viewed from the matching circuit18to the node N1. Therefore, the fundamental wave output from the main amplifier10is hardly reflected at the node N1. The impedance conversion circuit34rotates the impedance viewed from the matching circuit18to the node N1by 180° clockwise around the reference impedance66inFIG.2to convert it into the impedance viewed from the impedance conversion circuit34to the node N3. Thus, the impedance conversion circuit34functions as an impedance conversion circuit for converting the impedance on the substantially real axis64inFIG.2at the node N1into the impedance on the substantially real axis64at the node N3with respect to the fundamental wave. The fundamental wave output from the peak amplifier20is hardly reflected at the node N3.

As described above, a reflection coefficient at the node N1of the second harmonic wave transmitted from the main amplifier10to the node N1is larger than a reflection coefficient of the fundamental wave transmitted from the main amplifier10to the node N1, and a reflection coefficient at the node N3of the second harmonic wave transmitted from the peak amplifier20to the node N3is larger than a reflection coefficient of the fundamental wave transmitted from the peak amplifier20to the node N3.

The fundamental waves amplified by the main amplifier10and the peak amplifier20are combined at the node N3, and the combined fundamental wave is output from the output terminal Tout. On the other hand, the second harmonic waves generated in the main amplifier and the peak amplifier20are reflected at the nodes N1and N3, respectively, and are hardly output from the output terminal Tout. Therefore, the high frequency characteristics of the Doherty amplifier100can be improved. It is to be noted that the phases of the fundamental waves amplified by the main amplifier10and the peak amplifier20at the node N3are adjusted by the phase adjustment circuit32or the like so that the phases of the fundamental waves at the node N3are the same as each other.

As described above, since the main amplifier10and the peak amplifier20do not need to be provided with the harmonic tuning circuits, respectively, the Doherty amplifier can be reduced in size. Even when one harmonic tuning circuit40is used, the harmonic wave can be processed to the same extent as when the main amplifier10and the peak amplifier20are respectively provided with the harmonic tuning circuits. Therefore, it is possible to improve the harmonic characteristics of the Doherty amplifier100.

First Variation of First Embodiment

FIG.3is a block diagram of a Doherty amplifier according to a first variation of the first embodiment. As illustrated inFIG.3, in a Doherty amplifier101of the first variation of the first embodiment, the matching circuit18is not provided in the main amplifier10, but a harmonic phase adjustment circuit17is provided instead of the matching circuit18. The matching circuit28is not provided in the peak amplifier20, and a harmonic phase adjustment circuit27is provided instead of the matching circuit28. A matching circuit38is provided between the node N3and the impedance conversion circuit36. Other configurations are the same as those of the first embodiment, and description thereof is omitted.

The matching circuit38may be provided between the node N3and the output terminal Tout without providing the matching circuit18in the main amplifier10and the matching circuit28in the peak amplifier20as in the first variation of the first embodiment. When there is only one matching circuit38on the output side, the load impedances of both of the amplifying elements12and22may not be optimized. In such a case, the load impedance of the amplifying element12is preferentially optimized. In the first embodiment, the matching circuits18and28may adjust the phases of the second harmonic waves in anticipation of the second harmonic waves being reflected at the nodes N1and N3. In such a case, in the first variation of the first embodiment, the harmonic phase adjustment circuits17and27for adjusting the phases of the second harmonic waves are provided. The harmonic phase adjustment circuits17and27may not be provided.

Second Variation of First Embodiment

Second and third variations of the first embodiment are examples of an inverse Doherty amplifier having the impedance conversion circuit between the peak amplifier and the combining node.FIG.4is a block diagram of the Doherty amplifier according to the second variation of the first embodiment. As illustrated inFIG.4, in a Doherty amplifier102of the second variation of the first embodiment, the impedance conversion circuit34is provided between the nodes N2and N3. The harmonic tuning circuit40is connected to a line between the peak amplifier20and the node N3at the node N2. Other configurations are the same as those of the first embodiment, and description thereof is omitted.

In the second variation of the first embodiment, the first end of the harmonic tuning circuit40is connected to the node N2. The node N4to which the harmonic tuning circuit40is connected to the signal line and the node N2substantially coincide with each other. The harmonic tuning circuit40substantially short-circuits the nodes N2and N4with respect to the reference potential in the second harmonic wave, and does not short-circuit the nodes N2and N4with respect to the reference potential in the fundamental wave, so that the nodes N2and N4are in a state close to open, for example. Thus, the fundamental wave of the signal output from the peak amplifier20is hardly reflected at the node N2and passes through the node N2. The second harmonic wave is mostly reflected at the node N2and does not pass through the node N2. The node N3and the ground are substantially short-circuited in the second harmonic wave by the impedance conversion circuit34. On the other hand, the fundamental wave does not short-circuit between the node N3and the ground. Therefore, the fundamental wave of the signal output from the main amplifier10is hardly reflected at the node N3and passes through the node N3. The second harmonic wave is mostly reflected at the node N3. In this way, the fundamental waves amplified by the main amplifier10and the peak amplifier20are combined at the node N3and output from the output terminal Tout. The second harmonic waves generated in the main amplifier10and the peak amplifier20are reflected at the nodes N3and N2, respectively, and are hardly output from the output terminal Tout.

Third Variation of First Embodiment

FIG.5is a block diagram of a Doherty amplifier according to a third variation of the first embodiment. As illustrated inFIG.5, in a Doherty amplifier103of the third variation of the first embodiment, the matching circuit18is not provided in the main amplifier10, but the harmonic phase adjustment circuit17is provided instead of the matching circuit18. The matching circuit28is not provided in the peak amplifier20, and the harmonic phase adjustment circuit27is provided instead of the matching circuit28. The matching circuit38is provided between the node N3and the impedance conversion circuit36. Other configurations are the same as those of the second modification of the first embodiment, and description thereof will be omitted.

Second Embodiment

The second embodiment and the first modification thereof are examples of the forward Doherty amplifiers.FIG.6is a block diagram of a Doherty amplifier according to a second embodiment. As illustrated inFIG.6, in a Doherty amplifier104of the second embodiment, the first end of the harmonic tuning circuit40is connected to the node N3. In other words, the node N4at which the harmonic tuning circuit40is connected to the signal line and the node N3which is the combining node substantially coincide with each other. Other configurations are the same as those of the first embodiment, and description thereof is omitted.

The harmonic tuning circuit40short-circuits the nodes N3and N4with respect to the reference potential in the second harmonic wave, and does not short-circuits the nodes N3and N4with respect to the reference potential in the fundamental wave, so that the nodes N3and N4are in a state close to open, for example. Thus, the fundamental wave of the signal output from the peak amplifier20is hardly reflected at the node N3and passes through the node N3. The second harmonic wave is mostly reflected at the node N3. The node N1and the reference potential are short-circuited by the impedance conversion circuit34in the second harmonic wave. Therefore, the fundamental wave of the signal output from the main amplifier10passes through the node N1, and the second harmonic wave of the signal output from the main amplifier10is mostly reflected at the node N1. As described above, the second harmonic waves generated in the main amplifier10and the peak amplifier20are reflected at the nodes N1and N3, respectively, and are not output from the output terminal Tout.

In this way, the fundamental waves amplified by the main amplifier10and the peak amplifier20are combined at the node N3, and the combined fundamental wave is output from the output terminal Tout. On the other hand, the second harmonic waves generated in the main amplifier10and the peak amplifier20are reflected at the nodes N1and N3, respectively, and are hardly output from the output terminal Tout.

First Variation of Second Embodiment

FIG.7is a block diagram of a Doherty amplifier according to a first variation of the second embodiment. As illustrated inFIG.7, in a Doherty amplifier105of the first variation of the second embodiment, the matching circuit18is not provided in the main amplifier10, but the harmonic phase adjustment circuit17is provided instead of the matching circuit18. The matching circuit28is not provided in the peak amplifier20, and the harmonic phase adjustment circuit27is provided instead of the matching circuit28. The matching circuit38is provided between the node N3and the impedance conversion circuit36. Other configurations are the same as those of the second embodiment, and description thereof is omitted.

Second Variation of Second Embodiment

Second and third variations of the second embodiment are examples of an inverse Doherty amplifiers.FIG.8is a block diagram of a Doherty amplifier according to a second variation of the second embodiment. As illustrated inFIG.8, in a Doherty amplifier106of the second variation of the second embodiment, the impedance conversion circuit34is provided between the nodes N2and N3. Other configurations are the same as those of the second embodiment, and description thereof is omitted.

In the second variation of the second embodiment, the fundamental wave of the signal output from the main amplifier10is hardly reflected at the node N3and passes through the node N3, by the harmonic tuning circuit40. The second harmonic wave is mostly reflected at the node N3and does not pass through the node N3. By the impedance conversion circuit34, the node N2and the ground are not short-circuited in the fundamental wave but are short-circuited in the second harmonic wave. Therefore, the fundamental wave of the signal output from the peak amplifier20is hardly reflected at the node N2and passes through the node N3. The second harmonic wave is mostly reflected at the node N2. In this way, the fundamental waves amplified by the main amplifier10and the peak amplifier20are combined at the node N3and output from the output terminal Tout. The second harmonic waves generated by the main amplifier10and the peak amplifier20are reflected at the nodes N3and N2respectively and are hardly output from the output terminal Tout.

Third Variation of Second Embodiment

FIG.9is a block diagram of a Doherty amplifier according to a third variation of the second embodiment. As illustrated inFIG.9, in a Doherty amplifier107of the third variation of the second embodiment, the matching circuit18is not provided in the main amplifier10, but the harmonic phase adjustment circuit17is provided instead of the matching circuit18. The matching circuit28is not provided in the peak amplifier20, and the harmonic phase adjustment circuit27is provided instead of the matching circuit28. The matching circuit38is provided between the node N3and the impedance conversion circuit36. Other configurations are the same as those of the second variation of the second embodiment, and description thereof will be omitted.

Example of Harmonic Tuning Circuit40

FIGS.10to13are circuit diagrams illustrating examples of the harmonic tuning circuit in the first and the second embodiments and the variations thereof. As illustrated inFIG.10, the first end of the harmonic tuning circuit40is connected to a transmission line48at the node N4. A high frequency signal including the fundamental wave and the second harmonic wave flows through the transmission line48from left to right as indicated by an arrow. The harmonic tuning circuit40is an open stub. A first end of a stub42is connected to the transmission line48at the node N4. A second end of the stub42is open. When an electrical length D1from the node N4of the stub42is ⅛ of a wavelength k of the fundamental wave, the node N4is short-circuited with respect to the reference potential in the second harmonic wave, and the node N4is not short-circuited with respect to the reference potential in the fundamental wave. Thus, the second harmonic wave is reflected at the node N4. From the viewpoint of substantially short-circuiting the node N4with respect to the reference potential, the electrical length D1of the stub42is preferably 1λ/16 or more and 3λ/16 or less, more preferably 3λ/32 or more and 5λ/32 or less, and even more preferably 7λ/64 or more and 9λ/64 or less.

As illustrated inFIG.11, the harmonic tuning circuit40is a short stub. A first end of a stub44is connected to the transmission line48at the node N4, and a second end of the stub44is connected to a reference potential such as ground. When an electrical length D2from the node N4of the stub44to the reference potential is ¼ of the wavelength λ, of the fundamental wave, the node N4is short-circuited with respect to the reference potential in the second harmonic wave, and the node N4is opened with respect to the reference potential in the fundamental wave. Thus, the second harmonic wave is reflected at the node N4. From the viewpoint of substantially short-circuiting the node N4with respect to the reference potential, the electrical length D2of the stub44is preferably 3λ/16 or more and 5λ/16 or less, more preferably 7λ/32 or more and 9κ/32 or less, and even more preferably 15λ/64 or more and 17λ/64 or less. In the short stub, the node N4can be opened with respect to the reference potential in the fundamental wave, so that the reflection of the fundamental wave at the node N4can be made smaller.

As illustrated inFIG.12, the harmonic tuning circuit40is a CRLH (Composite Right/Left Handed) line. A transmission line45and capacitors C1and C2are connected in series between the node N4and the reference potential. An inductor L1is connected between the reference potential and a node between the transmission line45and the capacitor C1. An inductor L2is connected between the reference potential and the node between the capacitors C1and C2. By setting the capacitances of the capacitors C1and C2and the inductances of the inductors L1and L2to appropriate values, the node N4is short-circuited with respect to the reference potential in the second harmonic wave, and the node N4is not short-circuited with respect to the reference potential in the fundamental wave.

As illustrated inFIG.13, the harmonic tuning circuit40is a shunt capacitor. A capacitor C0is shunt-connected to the node N4. By shunt-connecting the capacitor C0, an absolute value of an impedance between the node N4and the reference potential in the second harmonic wave can be made smaller than an absolute value of an impedance between the node N4and the reference potential in the fundamental wave. Thus, the reflection coefficient of the second harmonic wave at the node N4becomes larger than the reflection coefficient of the fundamental wave. By appropriately selecting the capacitance of capacitor C0, a difference between the reflection coefficient of the second harmonic wave and the reflection coefficient of the fundamental wave at the node N4can be made larger.

As illustrated inFIGS.10to13, the harmonic tuning circuit40may make the absolute value of the impedance with respect to the reference potential at the node N4in the second harmonic wave smaller than the absolute value of the impedance with respect to the reference potential at the node N4in the fundamental wave. The absolute value of the impedance with respect to the reference potential at the node N4in the second harmonic wave is preferably ⅕ or less, more preferably 1/10 or less, and still more preferably 1/20 or less of the absolute value of the impedance with respect to the reference potential at the node N4in the fundamental wave.

It is preferable that the harmonic tuning circuit40short-circuits between the node N4and the reference potential in the second harmonic wave and does not short-circuit between the node N4and the reference potential in the fundamental wave. Thus, the reflection coefficient of the second harmonic wave at the node N4becomes almost 1, and the harmonic tuning circuit40reflects the second harmonic wave at the node N4. The fundamental wave almost passes through node N4. The short-circuit between the node N4and the reference potential in the frequency of the second harmonic wave means that the absolute value of the impedance between the node N4and the reference potential is ⅕ times or less of a reference impedance. More preferably, the absolute value of the impedance between the node N4and the reference potential is 1/10 times or less of the reference impedance.

As in the short stub ofFIG.11, the harmonic tuning circuit40opens between the node N4and the reference potential in the frequency of the fundamental wave. Thus, the reflection coefficient of the fundamental wave at the node N4becomes almost 0, and the harmonic tuning circuit40does not reflect the fundamental wave at the node N4. Here, the opening between the node N4and the reference potential in the frequency of the fundamental wave means that the absolute value of the impedance between the node N4and the reference potential is five times or more of the reference impedance. More preferably, the absolute value of the impedance between the node N4and the reference potential is 10 times or more of the reference impedance.

Example of Impedance Conversion Circuit34

FIGS.14to16are circuit diagrams illustrating examples of impedance conversion circuits according to the first and the second embodiments and the variations thereof. As illustrated inFIG.14, the impedance conversion circuit34is a transmission line35connected between the node N1or N2and the node N3. A high frequency signal including the fundamental wave and the second harmonic wave flows through the transmission line35from left to right as indicated by an arrow. An electrical length D3between the nodes N1or N2and N3in the transmission line35is ¼ of the wavelength λ, of the fundamental wave. Thereby, the phase of the fundamental wave at the node N3changes by 90° with respect to the node N1or N2, and the phase of the second harmonic wave at the node N3changes by 180° with respect to the node N1or N2. On the Smith chart ofFIG.2, the impedance at the node N3in the fundamental wave rotates by 180° around the reference impedance66with respect to the impedance at the node N1, and the impedance at the node N3in the second harmonic wave rotates by 360° around the reference impedance66with respect to the impedance at the node N1. An electric length D3is preferably 3/16 or more and 5/16 or less of the wavelength of the fundamental wave, more preferably 7/32 or more and 9/32 or less, and even more preferably 15/64 or more and 17/64 or less. The characteristic impedance of the transmission line35in the fundamental wave may be the reference impedance or may be different from the reference impedance.

As illustrated inFIG.15, the impedance conversion circuit34includes a transmission line35aand a capacitor C3connected in series between the node N1or N2and the node N3, and an inductor L3shunt-connected to the node between the transmission line35aand the capacitor C3. By appropriately designing the electrical length of the transmission line35a, the capacitance of the capacitor C3, and the inductance of the inductor L3, the impedance at the node N3in the fundamental wave can be rotated by 180° around the reference impedance66with respect to the impedance at the node N1, and the impedance at the node N3in the second harmonic wave can be rotated by 360° around the reference impedance66with respect to the impedance at the node N1on the Smith chart ofFIG.2. As an example, when the frequency of the fundamental wave is 2 GHz, the electrical length of the transmission line35ais made to correspond to the 23° phase of the fundamental wave, and the characteristic impedance of the transmission line35ais made to be 50Ω. The capacitance of the capacitor C3is 1.2 pF, and the inductance of the inductor L3is 3.4 nH. By providing the capacitor C3and the inductor L3, the electrical length of the transmission line35acan be made smaller than λ/4. Thus, the impedance conversion circuit34can be reduced in size.

As illustrated inFIG.16, the impedance conversion circuit34includes an inductor L4and a capacitor C4connected in series between the node N1or N2and the node N3. By appropriately designing the capacitance of the capacitor C4and the inductance of the inductor L4, the impedance at the node N3in the fundamental wave can be rotated by 180° around the reference impedance66with respect to the impedance at the node N1, and the impedance at the node N3in the second harmonic wave can be rotated by 360° around the reference impedance66with respect to the impedance at the node N1on the Smith chart ofFIG.2. As an example, when the frequency of the fundamental wave is 2 GHz, the capacitance of the capacitor C4is set to 0.1 pF and the inductance of the inductor L4is set to 15.805 nH. InFIG.16, since the transmission lines35and35aare not provided, the impedance conversion circuit34can be reduced in size.

As illustrated inFIGS.14to16, the impedance conversion circuit34may rotate the impedance at the node N3by 360° on the Smith chart with respect to the impedance at the node N1or N2in the second harmonic wave. The rotation of the impedance in the second harmonic wave need not be exactly 360°. The impedance conversion circuit34may rotate the impedance in the second harmonic wave within a range of 360°±45°. Thereby, the impedance of the short-circuit position60at the node N1or N2is located in a range between the positions68aand68bon the outer circumference inFIG.2, and is substantially short-circuited at the node N3. The impedance conversion circuit34preferably changes the impedance in the second harmonic wave within a range of 360°±22.5°, more preferably within a range of 360°±11.25°.

In the fundamental wave, the impedance conversion circuit34may rotate the impedance at the node N3by 180° on the Smith chart with respect to the impedance at the node N1or N2. The rotation of the impedance in the fundamental wave need not be strictly 180°. The impedance conversion circuit34may rotate the impedance of the fundamental wave within a range of 180°±22.5°. Thus, in the fundamental wave, the impedance conversion circuit34converts the impedance substantially on the real axis64at the node N1or N2into the impedance substantially on the real axis64at the node N3. The impedance conversion circuit34preferably changes the impedance in the fundamental wave within a range of 180°±11.25°, and more preferably within a range of 180°±5.625°.

[Position of Node N4in Second Embodiment and Variations Thereof]

In the second embodiment and the variations thereof, the position of the node N4to which the harmonic tuning circuit40is connected will be described.FIG.17is a plan view of the vicinity of the node N3in the second embodiment and the variations thereof. InFIG.17, three harmonic tuning circuits40are illustrated, indicating that one harmonic tuning circuit40is connected to any one of nodes N4ato N4c. As illustrated inFIG.17, there are provided a line50aextending from the main amplifier10to the node N3via the node N1, a line50bextending from the peak amplifier20to the node N3via the node N2, and a line50cextending from the node N3to the output terminal Tout. The lines50ato50care metal films provided on a dielectric layer56, and form a microstrip line along with a ground metal film under the dielectric layer56. The lines50ato50cmay be signal lines of a coplanar line. The node N3is a place where center lines52aand52bof the lines50aand50bintersect each other.

Preferably, the node N4to which the first end of the harmonic tuning circuit40is connected coincides with the node N3, but the node N4may not coincide with the node N3. The node N4may be provided on the line50alike the node N4a, on the line50blike the node N4b, or on the line50clike the node N4c. The nodes N4ato N4care positions at which center lines54ato54cof the line in the harmonic tuning circuit40intersect with the center lines52ato52c, respectively. When the electrical lengths between the node N3and the nodes N4ato N4cbecome large, the phase difference of the second harmonic waves between the node N1or N2and the nodes N4ato N4cbecomes non-negligible, and the second harmonic wave is not reflected at the node N1or N2. From this viewpoint, the electrical lengths D5between the node N3and the nodes N4ato N4care preferably 1/16 or less, more preferably 1/32 or less, and even more preferably 1/64 or less of the wavelength of the fundamental wave.

The electric length D5can be calculated from the physical lengths of the center lines52ato52cbetween a point where the center lines52aand52bintersect and points where the center lines52ato52cand54ato54cintersect, taking into consideration the relative dielectric constant of the dielectric layer56. The electrical length between the node N1or N2and the node N3in the first embodiment and the variations thereof can be calculated in the same manner.

An efficiency with respect to an output power was simulated for the Doherty amplifier102illustrated inFIG.4in the second variation of the first embodiment. For comparison, the efficiency with respect to the output power was simulated for the first and the second comparative examples.

FIG.18is a block diagram of the Doherty amplifier according to the second comparative example. As illustrated inFIG.18, in a Doherty amplifier110of the second comparative example, a first end of a harmonic tuning circuit40ais connected to a node N4dbetween the amplifying element12and the matching circuit18, and a first end of a harmonic tuning circuit40bis connected to a node N4ebetween the amplifying device22and the matching circuit28. Other configurations are the same as those of the Doherty amplifier of the second variation of the first embodiment illustrated inFIG.4. In the first comparative example, the harmonic tuning circuits40aand40bare not provided inFIG.18. The frequency of the fundamental wave is 3.5 GHz, the impedance conversion circuit34is a transmission line having an electrical length of ¼ of the wavelength of the fundamental wave and having a characteristic impedance of 50Ω, and the harmonic tuning circuits40,40a, and40bare short stubs having an electrical length of ¼ of the wavelength of the fundamental wave.

FIG.19is a diagram illustrating an efficiency with respect to an output power P in the first comparative example.FIG.20is a diagram illustrating an efficiency with respect to an output power P in a second comparative example.FIG.21is a diagram illustrating an efficiency with respect to an output power P in a second variation of the first embodiment. InFIGS.19to21, the efficiency is a drain efficiency. A marker m1indicates a position of the saturated output power Psat, and a marker m2is a position back-off from the saturated output power Psat by about 7 dBm.

As illustrated inFIG.19, in the first comparative example, the efficiencies of the markers m1and m2are 56.1% and 51.9%, respectively. As illustrated inFIG.20, in the second comparative example, the efficiencies of the markers m1and m2are 58.8% and 56.1%, respectively. As in the second comparative example, by providing the harmonic tuning circuits40aand40bin the main amplifier10and the peak amplifier20, respectively, the output of the second harmonic wave to the output terminal Tout can be suppressed, and the efficiency can be improved. As illustrated inFIG.21, in the second variation of the first embodiment, the efficiencies of the markers m1and m2are 58.1% and 55.8%, respectively. As in the second variation of the first embodiment, even if only one harmonic tuning circuit40is provided and the Doherty amplifier is reduced in size, the efficiencies can be approximately the same as the efficiencies of the second comparative example.

When the same simulation was performed in the Doherty amplifier107inFIG.9of the third variation of the second embodiment, the same result as that of the first variation of the first embodiment was obtained.

As in Patent Document 1, if the position of the node N4to which the harmonic tuning circuit is connected is not appropriately set even if only one harmonic tuning circuit is provided, both of the second harmonic wave output from the main amplifier10and the second harmonic wave output from the peak amplifier20cannot be appropriately processed. Therefore, if only one harmonic tuning circuit is provided and the Doherty amplifier is reduced in size, the harmonic characteristics are deteriorated and the efficiencies are reduced.

The first embodiment and the first variation thereof indicate the forward Doherty amplifiers. As illustrated inFIGS.1and3, a first amplifier that outputs the amplified signal to a first node N1is the main amplifier10, and a second amplifier that outputs the amplified signal of a second node N2is the peak amplifier20. The impedance conversion circuit34has a first end connected to the first node N1and a second end connected to the node N3. The first end of the harmonic tuning circuit40is connected to the line connecting the main amplifier10and a third node N3at the first node N1.

The second and the third variations of the first embodiment indicate the inverse Doherty amplifiers. As illustrated inFIGS.4and5, the first amplifier that outputs the amplified signal to the first node N2is the peak amplifier20, and the second amplifier that outputs the amplified signal of the second node N1is the main amplifier10. The impedance conversion circuit34has the first end connected to the first node N2and the second end connected to the node N3. The first end of the harmonic tuning circuit40is connected to the line connecting the peak amplifier20and the third node N3at the first node N2.

In such a forward Doherty amplifier and an inverse Doherty amplifier, the impedance conversion circuit34rotates the impedance viewed from the first amplifier to the node N3with respect to the impedance viewed from the first amplifier to the first node N1or N2within a range of 360°±45° on the Smith chart in the second harmonic wave. The harmonic tuning circuit40makes the absolute value of the impedance with respect to the reference potential at the node N4in the second harmonic wave smaller than the absolute value of the impedance with respect to the reference potential at the node N4in the fundamental wave. Thus, the second harmonic wave output from the first amplifier is mostly reflected at the first node N1or N2, and the second harmonic wave output from the second amplifier is mostly reflected at the third node N3. Therefore, both of the second harmonic wave output from the first amplifier and the second harmonic wave output from the second amplifier can be processed by the impedance conversion circuit34and the harmonic tuning circuit40, and the characteristics of the Doherty amplifier can be improved.

The second embodiment and the first variation thereof indicate the forward Doherty amplifiers. As illustrated inFIGS.6and7, the first amplifier which outputs the amplified signal to the first node N1is the main amplifier10, and the second amplifier which outputs the amplified signal of the second node N2is the peak amplifier20. The impedance conversion circuit34has the first end connected to the first node N1and the second end connected to the third node N3. The first end of the harmonic tuning circuit40is connected to a fourth node N4positioned on any of the third node N3, a first line connecting the main amplifier10and the third node N3, a second line connecting the peak amplifier20and the third node N3, and a third line connecting the third node N3and the output terminal Tout. The electrical length between the third node N3and the fourth node N4is 1/16 or less of the wavelength of the fundamental wave.

The second and the third variations of the second embodiment indicate the inverse Doherty amplifiers. As illustrated inFIGS.8and9, the first amplifier that outputs the amplified signal to the first node N2is the peak amplifier20, and the second amplifier that outputs the amplified signal of the second node N1is the main amplifier10. The impedance conversion circuit34has the first end connected to the first node N2and the second end connected to the third node N3. The first end of the harmonic tuning circuit40is connected to the fourth node N4positioned on any of the third node N3, the first line connecting the peak amplifier20and the third node N3, the second line connecting the main amplifier10and the third node N3, and the third line connecting the third node N3and the output terminal Tout. The electrical length between the third node N3and the fourth node N4is 1/16 or less of the wavelength of the fundamental wave.

In such a forward Doherty amplifier and an inverse Doherty amplifier, the impedance conversion circuit34rotates the impedance viewed from the first amplifier to the node N3with respect to the impedance viewed from the first amplifier to the first node N1or N2within a range of 360°±45° on the Smith chart in the second harmonic wave. The harmonic tuning circuit40makes the absolute value of the impedance with respect to the reference potential at the node N4in the second harmonic wave smaller than the absolute value of the impedance with respect to the reference potential at the node N4in the fundamental wave. Thus, the second harmonic wave output from the first amplifier is mostly reflected at the first node N1or N2, and the second harmonic wave output from the second amplifier is mostly reflected at the fourth node N4. Therefore, both of the second harmonic wave output from the first amplifier and the second harmonic wave output from the second amplifier can be processed by the impedance conversion circuit34and the harmonic tuning circuit40, and the characteristics of the Doherty amplifier can be improved.

As illustrated inFIGS.1and3to9, there is not provided a harmonic tuning circuit in which the first end is connected to the line connecting the second amplifier and the third node, and which makes the absolute value of the impedance with respect to the reference potential at the first end in the second harmonic wave smaller than the absolute value of the impedance with respect to the reference potential at the first end in the fundamental wave. Thus, since only one harmonic tuning circuit40is provided, the Doherty amplifier can be reduced in size.

The embodiments disclosed here should be considered illustrative in all respects and not restrictive. The present disclosure is not limited to the specific embodiments described above, but various variations and changes are possible within the scope of the gist of the present disclosure as described in the claims.