A power amplifier circuit includes a first transistor, a capacitor, and a second transistor. The first transistor has an emitter electrically connected to a reference potential, a base, and a collector electrically connected to a first power supply potential. A first end of the capacitor is electrically connected to the collector of the first transistor. The second transistor has an emitter electrically connected to a second end of the capacitor and electrically connected to the reference potential, a base, and a collector electrically connected to the first power supply potential. An RF output signal obtained by amplifying the RF input signal is output from the collector of the second transistor. A second bias circuit includes a third transistor having a collector electrically connected to a second power supply potential, a base, and an emitter from which the second bias current or voltage is output.

Amplifiers for radio-frequency applications. In some embodiments, a power amplifier die can include a semiconductor substrate and a plurality of narrow band power amplifiers implemented on the semiconductor substrate. Each narrow band power amplifier can be configured to operate with a high voltage in an average power tracking mode and be capable of being coupled to an output filter associated with a respective individual frequency band. Each narrow band power amplifier can be sized smaller than a wide band power amplifier configured to operate with more than one of the frequency bands associated with the plurality of narrow band power amplifiers.

Amplifiers for radio-frequency applications. In some embodiments, a power amplifier die can include a semiconductor substrate and a plurality of narrow band power amplifiers implemented on the semiconductor substrate. Each narrow band power amplifier can be configured to operate with a high voltage in an average power tracking mode and be capable of being coupled to an output filter associated with a respective individual frequency band. Each narrow band power amplifier can be sized smaller than a wide band power amplifier configured to operate with more than one of the frequency bands associated with the plurality of narrow band power amplifiers.

A power amplifier circuit includes an amplifier transistor having a first terminal supplied with a power supply voltage that changes in accordance with an amplitude level of an input signal, and a second terminal supplied with the input signal and a bias current, an amplified signal obtained by amplifying the input signal being outputted from the first terminal, a bias circuit that outputs the bias current from an output terminal thereof in accordance with a reference current supplied to an input terminal thereof, and a regulation circuit that generates a regulation current for regulating the bias current in accordance with a change in the power supply voltage. The regulation current increases with an increase in the power supply voltage, and decreases with a decrease in the power supply voltage. The regulation circuit extracts the regulation current from at least one of the reference current or the bias current.

A bias circuit includes a bias current circuit and a temperature compensation circuit. The bias current circuit includes a first resistor and a first transistor, in a first current path connected between a current terminal of a reference current and a ground, and connected to each other in series, and a second transistor in a second current path connected between the current terminal and the ground, and having a base connected to a collector of the first transistor. The temperature compensation circuit includes a second resistor in the second current path, and connected between an emitter of the second transistor and a base of the first transistor and having a first thermal coefficient, and a third resistor included in the second current path, and connected between the base of the first transistor and the ground and having a second thermal coefficient, different from the first thermal coefficient.

Provided is a power amplification module that includes: a first transistor, a first signal being inputted to a base thereof; a second transistor, the first signal being inputted to a base thereof and a collector thereof being connected to a collector of the first transistor; a first resistor, a first bias current being supplied to one end thereof and another end thereof being connected to the base of the first transistor; a second resistor, one end thereof being connected to the one end of the first resistor and another end thereof being connected to the base of the second transistor; and a third resistor, a second bias current being supplied to one end thereof and another end thereof being connected to the base of the second transistor.

Power amplifiers having reduced loss. In some embodiments, a power amplification system can include a plurality of power amplifiers, with each power amplifier being configured to receive and amplify a signal in a frequency band. The power amplification system can further include an output filter coupled to each of the power amplifiers by a separate output path such that the power amplification system is substantially free of a band selection switch between the plurality of power amplifiers and their corresponding output filters. Each power amplifier can be further configured to operate with a high-voltage supply to provide an impedance similar to an impedance of the corresponding output filter.

Power amplifiers having reduced loss. In some embodiments, a power amplification system can include a plurality of power amplifiers, with each power amplifier being configured to receive and amplify a signal in a frequency band. The power amplification system can further include an output filter coupled to each of the power amplifiers by a separate output path such that the power amplification system is substantially free of a band selection switch between the plurality of power amplifiers and their corresponding output filters. Each power amplifier can be further configured to operate with a high-voltage supply to provide an impedance similar to an impedance of the corresponding output filter.

Provided is a power amplification module that includes: a first amplification circuit that amplifies a first signal and outputs the amplified first signal as a second signal; a second amplification circuit that amplifies the second signal and outputs the amplified second signal as a third signal; and a feedback circuit that re-inputs/feeds back the second signal outputted from the first amplification circuit to the first amplification circuit as the first signal. The operation of the first amplification circuit is halted and the first signal passes through the feedback circuit and is outputted as the second signal at the time of a low power output mode.

Provided is a power amplification module that includes: a first amplification circuit that amplifies a first signal and outputs the amplified first signal as a second signal; a second amplification circuit that amplifies the second signal and outputs the amplified second signal as a third signal; and a feedback circuit that re-inputs/feeds back the second signal outputted from the first amplification circuit to the first amplification circuit as the first signal. The operation of the first amplification circuit is halted and the first signal passes through the feedback circuit and is outputted as the second signal at the time of a low power output mode.