A radiofrequency power amplifier includes a balun transformer and a plurality of power transistor pairs arranged in a push-pull configuration. The balun transformer has an unbalanced coil extending between a first single-ended signal terminal and a first reference, and a balanced coil extending between a first balanced signal terminal and a second balanced signal terminal. The balun transformer also includes an auxiliary coil electrically isolated from the unbalanced coil and the balanced coil. The auxiliary coil is inductively coupled to the unbalanced coil and extends between a third balanced signal terminal and a fourth balanced signal terminal forming a balanced combiner-divider. An output of a first one of the power transistor pairs is coupled to the first and second balanced signal terminals and an output of a second one of the power transistor pairs is coupled to the third and fourth balanced signal terminals.

Provided is a variable filter circuit that can control the bandwidth and center frequency of a pass band, can realize steep attenuation characteristics in bands close to the pass band, and enables the total number of variable reactance units to be reduced. A variable filter circuit includes an inductor (Ls1) and a capacitor (Cs1), which are connected in series between a first input/output terminal (P1) and a second input/output terminal (P2), and resonators (Re_p1, Re_p2, Re_p3, Re_p4) and variable capacitors (Cc1, Cc2, Cc3, Cc4), which are connected in series between two ends of the inductor (Ls1) and the capacitor (Cs1) and ground connection terminals.

A power amplification circuit that includes: a capacitor element in which a first metal layer, a first insulating layer, a second metal layer, a second insulating layer and a third metal layer are sequentially stacked, the capacitor element including a first capacitor in which the first metal layer serves as one electrode thereof and the second metal layer serves as another electrode thereof, and a second capacitor in which the second metal layer serves as one electrode thereof and the third metal layer serves as another electrode thereof; and a transistor that amplifies a radio-frequency signal. The radio-frequency signal is supplied to the one electrode of the first capacitor. The other electrode of the first capacitor and the one electrode of the second capacitor are connected to a base of the transistor, and the other electrode of the second capacitor is connected to the emitter of the transistor.

Aspects of this disclosure relate to an amplification circuit that includes a stacked amplifier and a bias circuit. The stacked amplifier includes at least a first transistor and a second transistor in series with each other. The stacked amplifier is operable in at least a first mode and a second mode. The bias circuit is configured to bias the second transistor to a linear region of operation in the first mode and to bias the second transistor as a switch in the second mode. In certain embodiments, the amplification circuit can be a power amplifier stage configured to receive a supply voltage that has a different voltage level in the first mode than in the second mode.

Aspects of this disclosure relate to an amplification circuit that includes a stacked amplifier and a bias circuit. The stacked amplifier includes at least a first transistor and a second transistor in series with each other. The stacked amplifier is operable in at least a first mode and a second mode. The bias circuit is configured to bias the second transistor to a linear region of operation in the first mode and to bias the second transistor as a switch in the second mode. In certain embodiments, the amplification circuit can be a power amplifier stage configured to receive a supply voltage that has a different voltage level in the first mode than in the second mode.

A power amplifier circuit includes a power splitter, a first amplifier configured to output a first amplified signal from a first output terminal, and a second amplifier configured to output a second amplified signal from a second output terminal. The power amplifier circuit further includes a first termination circuit connected between the first output terminal and the second output terminal, a first transmission line, a second transmission line, a second termination circuit connected between another end of the first transmission line and another end of the second transmission line, and a power combiner.

A power amplifier circuit includes a power splitter, a first amplifier configured to output a first amplified signal from a first output terminal, and a second amplifier configured to output a second amplified signal from a second output terminal. The power amplifier circuit further includes a first termination circuit connected between the first output terminal and the second output terminal, a first transmission line, a second transmission line, a second termination circuit connected between another end of the first transmission line and another end of the second transmission line, and a power combiner.

A filter allows a transmission signal in a predetermined frequency band to pass from a second input-output terminal to a first input-output terminal and allows a reception signal in the predetermined frequency band to pass from the first input-output terminal to the second input-output terminal. A first common terminal of a first switch is connected to the second input-output terminal. A second terminal and a first terminal of the first switch are exclusively connectable to the first common terminal. A second common terminal of a second switch is connected to a ground terminal of the filter. A second selection terminal and a first selection terminal of the second switch are exclusively connected to the second common terminal. Of the first selection terminal and the second selection terminal, only the first selection terminal is connected to a ground with a reactive element interposed therebetween.

A high frequency amplifier includes a high frequency amplifier transistor integrated in a first die of a first semiconductor technology and a matching circuit. The high frequency amplifier transistor has an input terminal, an output terminal and a reference terminal. The reference terminal is coupled to a reference potential. The matching circuit includes at least a first inductive bondwire, a second inductive bondwire and a capacitive element arranged in series with said inductive bondwires. The capacitive element is integrated in a second die of a second semiconductor technology different from the first semiconductor technology. The second semiconductor technology includes an isolating substrate for conductively isolating the capacitive element from a support attached at a first side to the second die. The capacitive element includes a first plate electrically coupled to a first bondpad of the second die and a second plate electrically coupled to a second bondpad of the second die.

A high frequency amplifier includes a high frequency amplifier transistor integrated in a first die of a first semiconductor technology and a matching circuit. The high frequency amplifier transistor has an input terminal, an output terminal and a reference terminal. The reference terminal is coupled to a reference potential. The matching circuit includes at least a first inductive bondwire, a second inductive bondwire and a capacitive element arranged in series with said inductive bondwires. The capacitive element is integrated in a second die of a second semiconductor technology different from the first semiconductor technology. The second semiconductor technology includes an isolating substrate for conductively isolating the capacitive element from a support attached at a first side to the second die. The capacitive element includes a first plate electrically coupled to a first bondpad of the second die and a second plate electrically coupled to a second bondpad of the second die.