An amplifier circuit includes a first amplifier and a second amplifier. The first amplifier receives a first signal and generates a first amplification signal accordingly. The second amplifier receives a second signal and generates a second amplification signal accordingly. The first signal is related to a first frequency band, and the second signal is related to a second frequency band different from the first frequency band. When one of the first amplifier and the second amplifier is in use, the other one of the first amplifier and the second amplifier is unused. The first amplifier and second amplifier are coupled to a reference voltage terminal through a common node. The first amplifier includes a switch coupled between the common node and a stage of the first amplifier, and the switch can be controlled for reducing the loading effect caused by the first amplifier on the second amplifier.

An amplifier comprising a main branch amplifier and an auxiliary branch amplifier, wherein one branch is a constant current-biased branch, and another branch is a voltage biased branch, with the branches connected in cascode configuration to form a load modulated amplifier.

An amplifier circuit includes an input terminal to which a radio frequency signal is input, an amplifier transistor that has a control terminal and amplifies the radio frequency signal, a bias circuit that includes an emitter-follower circuit or a source-follower circuit and supplies a bias current to the control terminal of the amplifier transistor, an inductor arranged in series between an emitter of the emitter-follower circuit and the control terminal of the amplifier transistor or between a source of the source-follower circuit and the control terminal of the amplifier transistor, and a variable resistance circuit connected to the inductor.

A first branch group circuit includes a first branch circuit receiving a first RF input signal and first control information; and a second branch circuit receiving the first input signal and second control information. Each of the first and second branch circuits includes a power amplifier. The second control information enables the second branch circuit to be switched on or off while the first branch circuit remains on. A second branch group circuit includes: a third branch circuit receiving a second RF input signal and third control information; and a fourth branch circuit receiving the second input signal and fourth control information. Each of the third and fourth branch circuits includes a power amplifier. The fourth control information enables the fourth branch circuit to be switched on or off while the third branch circuit remains on. A combiner combines output signals of the power amplifiers to produce an output signal.

A transformer-based Doherty power amplifier includes a main power amplifier path and an auxiliary power amplifier path which are connected in parallel. The main power amplifier path includes a main power amplifier, and the auxiliary power amplifier path includes an auxiliary power amplifier. The transformer-based Doherty power amplifier further includes a first linear network circuit or a second linear network circuit. The first linear network circuit is arranged at an input of the main power amplifier and is used to compensate for variations of an input capacitance of the main power amplifier, so as to improve the linearity of the main power amplifier. The second linear network circuit is arranged at an input of the auxiliary power amplifier and is used to compensate for variations of an input capacitance of the auxiliary power amplifier, so as to improve the linearity of the auxiliary power amplifier.

A power amplifying device according to an embodiment includes first to fourth BTL amplifiers and first to third switch circuits. The first to fourth BTL amplifiers outputs a first to fourth output signal. The first switch circuit is turned on or off connection between an output of the second output amplifier and an output of the third output amplifier. The second switch circuit is turned on or off connection between an output of the fifth output amplifier and an output of the eighth output amplifier. The third switch circuit is turned on or off connection between an output of the fourth output amplifier and an output of the seventh output amplifier. The first to third switch circuits are turned on when the amplitudes of the first to fourth input signals are smaller than a first threshold.

A balanced power amplifier includes a first power amplifier configured to apply a first gain having a first predetermined magnitude and a first programmable phase adjustable phase to generate a first amplified signal, the first programmable phase being adjustable to either a first phase or to a second phase that is 180° phase shifted relative to the first phase; a second power amplifier configured to apply a second gain having a second predetermined magnitude and a second programmable phase to generate a second amplified signal, the second programmable phase being adjustable to either the first phase or to the second phase; and a 90° hybrid coupler configured to receive the first amplified signal and the second amplified signal and generate and output a first output signal or a second output signal based on a combination of the first amplified signal and the second amplified signal.

Radio frequency (RF) filters configured to filter undesired signal components (e.g., noise and harmonics) from RF signals are disclosed. In one embodiment, an RF filter includes a first inductor coil having a first winding and a second inductor coil having a second winding and a third winding. The second winding of the second inductor coil is configured to have a first mutual magnetic coupling with the first winding, while the third winding of the second inductor coil is configured to have a second mutual magnetic coupling with the first winding. The second winding is connected to the third winding such that the first mutual magnetic coupling and the second mutual magnetic coupling are in opposition. In this manner, the first inductor coil and the second inductor coil may be provided in a compact arrangement while providing weak mutual magnetic coupling between the first inductor coil and the second inductor coil.

A power amplifier module includes an amplifier transistor and a bias circuit. A first power supply voltage based on a first operation mode or a second power supply voltage based on a second operation mode is supplied to the amplifier transistor. The amplifier transistor receives a first signal and outputs a second signal obtained by amplifying the first signal. The bias circuit supplies a bias current to the amplifier transistor. The bias circuit includes first and second resistors and first and second transistors. The first transistor is connected in series with the first resistor and is turned ON by a first bias control voltage which is supplied when the first operation mode is used. The second transistor is connected in series with the second resistor and is turned ON by a second bias control voltage which is supplied when the second operation mode is used.

Circuits and devices related to radio-frequency amplifiers. In some embodiments, a radio-frequency amplifier can include a plurality of narrow band power amplifiers. 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.