This application claims priority from Japanese Patent Application No. 2019-104227 filed on Jun. 4, 2019, and claims priority from Japanese Patent Application No. 2019-232959 filed on Dec. 24, 2019. The contents of these applications are incorporated herein by reference in their entireties.

BACKGROUND

The present disclosure relates to a power amplifier circuit. In communications using radio frequency (RF) signals of mobile units, such as cellular phones, a power amplifier circuit is used to amplify an RF signal. As a control method for efficiently amplifying an RF signal, there is envelope tracking (ET) control. In ET control, power is amplified by using a power supply voltage that varies in accordance with an envelope of the amplitude of a radio frequency signal.

In performing ET control, a harmonic component, such as a second harmonic component, of an RF signal has to be appropriately dealt with in the power amplifier circuit. Japanese Unexamined Patent Application Publication No. 2010-87934 discloses RF power amplifier that inhibits leakage of power of a second harmonic component with twice the frequency of a fundamental.

In the power amplifier circuit that performs ET control, a power supply voltage is controlled so that a saturation region of operation of a transistor is used. In the case where the transistor is caused to operate in the saturation region at a power supply voltage, output power of the transistor at the power supply voltage is high. When the output power is high, not only a fundamental component of an RF signal but also harmonic components increase. When a harmonic power amplifier that adjusts an impedance only for a second harmonic component as described in Japanese Unexamined Patent Application Publication No. 2010-87934 is used, impedance of third and higher harmonic components are not adjusted. A power amplifier circuit in this case is affected by third and higher harmonic components, and a region where the efficiency of a transistor is maximized is therefore not used for each power supply voltage subjected to ET control. The region where the efficiency is maximized is not used, and thus optimization of the power amplifier circuit that performs ET control is not able to be achieved.

BRIEF SUMMARY

The present disclosure has been made in consideration of such circumstances and provides a power amplifier circuit that efficiently amplifies power when a radio frequency signal is amplified by performing envelope tracking control.

A power amplifier circuit according to an aspect of the present disclosure includes a transistor having a base to which a radio frequency signal is input and a collector to which a power supply voltage that varies in accordance with an envelope of amplitude of the radio frequency signal is supplied and from which an amplified signal obtained by amplifying the radio frequency signal is output; a first termination circuit provided at a stage subsequent to the transistor and configured to attenuate a harmonic component of the amplified signal; and a second termination circuit provided at the stage subsequent to the transistor and configured to attenuate a harmonic component of the amplified signal. The first termination circuit and the second termination circuit have a property of resonating for a radio frequency signal having a frequency between a frequency of a second harmonic component and a frequency of a third harmonic component.

The present disclosure can provide the power amplifier circuit that efficiently amplifies power when a radio frequency signal is amplified by performing envelope tracking control.

Other features, elements, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of embodiments of the present disclosure with reference to the attached drawings.

