A high frequency amplification circuit includes transmission amplification circuits 11 and 12; a transmission filter D-Tx whose pass band is a band D of a first frequency band group; transmission filters E-Tx and G-Tx whose pass bands are respectively bands E and G of a second frequency band group; an output matching circuit 31 configured to match the transmission amplification circuit 11 and the transmission filter D-Tx; and an output matching circuit 32 configured to match the transmission amplification circuit 12 and the transmission filters E-Tx and G-Tx. The band D is positioned at a high frequency-side end portion of the first frequency band group, and the band E is positioned at a low frequency-side end portion of the second frequency band group. The output matching circuit 31 includes a low-pass circuit, and the output matching circuit 32 includes an impedance-variable circuit.

A high frequency amplification circuit includes transmission amplification circuits 11 and 12; a transmission filter D-Tx whose pass band is a band D of a first frequency band group; transmission filters E-Tx and G-Tx whose pass bands are respectively bands E and G of a second frequency band group; an output matching circuit 31 configured to match the transmission amplification circuit 11 and the transmission filter D-Tx; and an output matching circuit 32 configured to match the transmission amplification circuit 12 and the transmission filters E-Tx and G-Tx. The band D is positioned at a high frequency-side end portion of the first frequency band group, and the band E is positioned at a low frequency-side end portion of the second frequency band group. The output matching circuit 31 includes a low-pass circuit, and the output matching circuit 32 includes an impedance-variable circuit.

A power amplifier includes power amplification circuits in a plurality of stages including a first stage and a second stage, each power amplification circuit including a transistor. The power amplification circuit in the first stage includes a first impedance circuit between an emitter of the transistor and a reference potential. The first impedance circuit has an impedance that does not vary with frequency or an impedance that varies with frequency. The power amplification circuit in the second stage includes a second impedance circuit between an emitter of the transistor and a reference potential. The second impedance circuit has an impedance that does not vary with frequency or an impedance that varies with frequency.

An RF amplifier for implementation in SiGe HBT technology is described. The RF amplifier has a cascode stage comprising a common base (CB) transistor and a common emitter (CE) transistor arranged in series between a first voltage rail and a second voltage rail. An RF input is coupled to the base of the CE transistor and an RF output is coupled to the collector of the CB transistor. The RF amplifier includes a CB power-down circuit arranged between the base of the CB transistor and the second voltage rail and a CE power-down circuit arranged between the base of the CE transistor and the second voltage rail. In a power-down mode the CE power-down circuit couples the base of the common-emitter-transistor to the second voltage rail. The CB power-down mode circuit couples the base of the CB transistor to the second voltage rail via a high-ohmic path.

A radio frequency amplifier includes a transistor, an input impedance matching circuit (e.g., a single-section T-match circuit or a multiple-section bandpass circuit), and a fractional harmonic resonator circuit. The input impedance matching circuit is coupled between an amplification path input and a transistor input terminal. An input of the fractional harmonic resonator circuit is coupled to the amplification path input, and an output of fractional harmonic resonator circuit is coupled to the transistor input terminal. The fractional harmonic resonator circuit is configured to resonate at a resonant frequency that is between a fundamental frequency of operation of the RF amplifier and a second harmonic of the fundamental frequency. According to a further embodiment, the fractional harmonic resonator circuit resonates at a fraction, x, of the fundamental frequency, wherein the fraction is between about 1.25 and about 1.9 (e.g., x≈1.5).

A power amplification module includes: a first bipolar transistor in which a radio frequency signal is input to a base and an amplified signal is output from a collector; a second bipolar transistor that is thermally coupled with the first bipolar transistor and that imitates operation of the first bipolar transistor; a third bipolar transistor in which a first control voltage is supplied to a base and a first bias current is output from an emitter; a first resistor that generates a third control voltage corresponding to a collector current of the second bipolar transistor at a second terminal; and a fourth bipolar transistor in which a power supply voltage is supplied to a collector, the third control voltage is supplied to a base, and a second bias current is output from an emitter.

A power amplification module includes: a first bipolar transistor in which a radio frequency signal is input to a base and an amplified signal is output from a collector; a second bipolar transistor that is thermally coupled with the first bipolar transistor and that imitates operation of the first bipolar transistor; a third bipolar transistor in which a first control voltage is supplied to a base and a first bias current is output from an emitter; a first resistor that generates a third control voltage corresponding to a collector current of the second bipolar transistor at a second terminal; and a fourth bipolar transistor in which a power supply voltage is supplied to a collector, the third control voltage is supplied to a base, and a second bias current is output from an emitter.

In some embodiments, a power amplification system can comprise a current source, an input switch configured to alternatively feed current from the current source to a high-power circuit path and a low-power circuit path, and a band switch including a switch arm for switching between a plurality of bands. Each of the high-power circuit path and the low-power circuit path can be connected to the switch arm.

Apparatus and methods for bias switching of power amplifiers are provided herein. In certain configurations, a power amplifier system includes a power amplifier that provides amplification to a radio frequency (RF) signal, a power management circuit that controls a voltage level of a supply voltage of the power amplifier, and a bias control circuit that biases the power amplifier. The power management circuit is operable in multiple supply control modes, such as an average power tracking (APT) mode and an envelope tracking (ET) mode. The bias control circuit is configured to switch a bias of the power amplifier based on the supply control mode of the power management circuit.

A first power amplifier amplifies first transmission signals in a first frequency band and outputs the resultant signals. A first matching circuit includes a plurality of first inductor portions and is connected to an output pad electrode of the first power amplifier. A second power amplifier amplifies second transmission signals in a second frequency band higher than the first frequency band and outputs the resultant signals. A second matching circuit includes at least one second inductor portion and is connected to an output side of the second power amplifier. A multilayer substrate has a first main surface and a second main surface located opposite to each other and is provided with the first and second power amplifiers and the first and second matching circuits. The first inductor portion closer than the other first inductor portions to the output pad electrode includes an inner-layer inductor portion located in the multilayer substrate.