US-12620940-B2 - Doherty amplifier

US12620940B2US 12620940 B2US12620940 B2US 12620940B2US-12620940-B2

Abstract

A Doherty amplifier includes: a carrier amplifier to amplify a first high frequency signal having a first higher harmonic and a second higher harmonic; a peak amplifier to amplify a second high frequency signal having the first higher harmonic and the second higher harmonic; a first series resonant circuit connected between an output end of the carrier amplifier and a ground, and configured to resonate at the frequency of the first higher harmonic; a second series resonant circuit connected between an output end of the peak amplifier and the ground, and configured to resonate at the frequency of the first higher harmonic; a first parallel resonant circuit configured to resonate at the frequency of the second higher harmonic; and a second parallel resonant circuit configured to resonate at the frequency of the second higher harmonic.

Inventors

Kazuhiro Iyomasa
Eigo Kuwata

Assignees

MITSUBISHI ELECTRIC CORPORATION

Dates

Publication Date: 20260505
Application Date: 20231018

Claims (6)

1 . A Doherty amplifier comprising: a carrier amplifier to amplify a first high frequency signal having a first higher harmonic and a second higher harmonic; a peak amplifier to amplify a second high frequency signal having the first higher harmonic and the second higher harmonic; a first series resonant circuit connected between an output end of the carrier amplifier and a ground, and configured to resonate at a frequency of the first higher harmonic; a second series resonant circuit connected between an output end of the peak amplifier and the ground, and configured to resonate at the frequency of the first higher harmonic; a first parallel resonant circuit having an end connected to the output end of the carrier amplifier, and another end connected to the output end of the peak amplifier, the first parallel resonant circuit being configured to resonate at a frequency of the second higher harmonic; and a second parallel resonant circuit having an end connected to the output end of the peak amplifier and the other end of the first parallel resonant circuit, and another end electrically connected to a load, the second parallel resonant circuit being configured to resonate at the frequency of the second higher harmonic.
2 . The Doherty amplifier according to claim 1 , wherein the Doherty amplifier comprises an output matching circuit having an end connected to the output end of the peak amplifier and the other end of the first parallel resonant circuit, and another end connected to the load, and including the second parallel resonant circuit, and the output matching circuit comprises, in addition to the second parallel resonant circuit, a capacitor connected between the other end of the second parallel resonant circuit and the ground, and an inductor having an end connected to the other end of the second parallel resonant circuit, and another end connected to the load.
3 . The Doherty amplifier according to claim 1 , wherein the first higher harmonic is a second harmonic of a fundamental wave contained in each of the first and second high frequency signals, and the second higher harmonic is a third harmonic of the fundamental wave, and wherein the first series resonant circuit and the second series resonant circuit form, for the second harmonic, a short-circuited end on an output side of each of the carrier and peak amplifiers, and the first parallel resonant circuit and the second parallel resonant circuit form, for the third harmonic, an open end on the output side of each of the carrier and peak amplifiers.
4 . The Doherty amplifier according to claim 1 , wherein the first higher harmonic is a third harmonic of a fundamental wave contained in each of the first and second high frequency signals, and the second higher harmonic is a second harmonic of the fundamental wave, and wherein the first series resonant circuit and the second series resonant circuit form, for the third harmonic, a short-circuited end on an output side of each of the carrier and peak amplifiers, and the first parallel resonant circuit and the second parallel resonant circuit form, for the second harmonic, an open end on the output side of each of the carrier and peak amplifiers.
5 . The Doherty amplifier according to claim 1 , wherein the first series resonant circuit is a series circuit in which an inductor and a capacitor are connected in series, and inductance of the inductor and capacitance of the capacitor are determined on a basis of parasitic capacitance of the carrier amplifier.
6 . The Doherty amplifier according to claim 1 , wherein the second series resonant circuit is a series circuit in which an inductor and a capacitor are connected in series, and inductance of the inductor and capacitance of the capacitor are determined on a basis of parasitic capacitance of the peak amplifier.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a Continuation of PCT International Application No. PCT/JP2021/020147, filed on May 27, 2021, which is hereby expressly incorporated by reference into the present application. TECHNICAL FIELD The present disclosure relates to a Doherty amplifier. BACKGROUND ART A Doherty amplifier including a carrier amplifier, a peak amplifier, and a load modulation circuit is disclosed in Patent Literature 1. This load modulation circuit includes a first parallel resonant circuit, a second parallel resonant circuit, and a third parallel resonant circuit. The first parallel resonant circuit has an end connected to an output end of the carrier amplifier, and another end connected to a ground. The second parallel resonant circuit has an end connected to an output end of the peak amplifier, and another end connected to the ground. The third parallel resonant circuit has an end connected to the output end of the carrier amplifier, and another end connected to the output end of the peak amplifier. Each of the first, second and third parallel resonant circuits undergoes parallel resonance at the frequency of a second harmonic which is one of multiple higher harmonics contained in a high frequency signal to be amplified. Each of the first, second and third parallel resonant circuits undergoes parallel resonance, and, as a result, the impedance, for the second harmonic, seen from each of the output ends of the carrier and peak amplifiers toward a load is infinite. CITATION LIST Patent Literature Patent Literature 1: WO No. 2020/235093 SUMMARY OF INVENTION Technical Problem In the Doherty amplifier disclosed in Patent Literature 1, the impedance, for the second harmonic, seen from each of the output ends of the carrier and peak amplifiers toward the load side is maintained in a state in which the impedance is fixed to infinity even when the impedance of the load changes. On the other hand, there is a case in which a change in the impedance of the load causes a change in the impedance, for a third harmonic, seen from each of the output ends of the carrier and peak amplifiers toward the load. More specifically, a problem with the Doherty amplifier disclosed in Patent Literature 1 is that the Doherty amplifier cannot prevent a change in the impedance for any higher harmonic other than the single type of higher harmonic. In the case where the Doherty amplifier cannot prevent a change in the impedance for any higher harmonic other than the single type of higher harmonic, a change in the impedance for any other higher harmonic may cause degradation in the operation efficiency of the Doherty amplifier. The present disclosure is made in order to solve the above-mentioned problem, and it is therefore an object of the present disclosure to provide a Doherty amplifier that can prevent a change in the impedance for each of first and second higher harmonics, the change being caused by a change in the impedance of a load. Solution to Problem A Doherty amplifier according to the present disclosure includes: a carrier amplifier to amplify a first high frequency signal having a first higher harmonic and a second higher harmonic; a peak amplifier to amplify a second high frequency signal having the first higher harmonic and the second higher harmonic; a first series resonant circuit connected between an output end of the carrier amplifier and a ground, and configured to resonate at the frequency of the first higher harmonic; a second series resonant circuit connected between an output end of the peak amplifier and the ground, and configured to resonate at the frequency of the first higher harmonic; a first parallel resonant circuit having an end connected to the output end of the carrier amplifier, and another end connected to the output end of the peak amplifier, the first parallel resonant circuit being configured to resonate at the frequency of the second higher harmonic; and a second parallel resonant circuit having an end connected to the output end of the peak amplifier and the other end of the first parallel resonant circuit, and another end electrically connected to a load, the second parallel resonant circuit being configured to resonate at the frequency of the second higher harmonic. Advantageous Effects of Invention According to the present disclosure, the Doherty amplifier can prevent a change in the impedance for each of the first and second higher harmonics, the change being caused by a change in the impedance of the load. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic diagram showing a Doherty amplifier 100 according to Embodiment 1; FIG. 2 is an equivalent circuit diagram showing the Doherty amplifier 100 shown in FIG. 1; FIG. 3 is an explanatory drawing showing concrete configurations of a load modulation circuit 8 and an output matching circuit 12 which are shown in FIG. 2; FIG. 4 is a Smith chart showing a result of the calculation of the impedance of the load modula