A radio frequency apparatus includes a power amplifier circuit, a signal coupling circuit, an extraction circuit, and a harmonic filter circuit. The power amplifier circuit is configured to amplify a differential signal to output a to-be-filtered signal. The signal coupling circuit includes a primary side inductor and a secondary side inductor. The signal coupling circuit is configured to convert the to-be-filtered signal received by the primary side inductor into a single-ended signal outputted from the secondary side inductor. The extraction circuit has a center tap. The extraction circuit is configured to inductively couple to the primary side inductor and output a common mode signal from the center tap. The harmonic filter circuit is configured to perform a harmonic filtering on the single-ended signal according to the common mode signal, such that the secondary side inductor of the signal coupling circuit outputs a filtered signal.

A power amplifying circuit includes a first input terminal applied with a first bias voltage, a first amplifying circuit generating a first output signal and a second output signal according to an input signal and a first matching circuit combining the first output signal and the second output signal to generate an output signal. The first amplifying circuit includes a first transistor having a first electrode coupled to the first input terminal and a second electrode applied with a second bias voltage and a second transistor having a first electrode s coupled to the first input terminal and a second electrode applied with a third bias voltage. The first transistor generates the first output signal according to the first bias voltage and the second bias voltage. The second transistor generates the second output signal according to the first bias voltage and the third bias voltage.

A Doherty amplifier circuit comprising: a splitter having: a splitter-input-terminal for receiving an input signal; a main-splitter-output-terminal; and a peaking-splitter-output-terminal; a main-power-amplifier having a main-power-input-terminal and a main-power-output-terminal, wherein; the main-power-input-terminal is connected to the main-splitter-output-terminal; and the main-power-output-terminal is configured to provide a main-power-amplifier-output-signal; a peaking-power-amplifier having a peaking-power-input-terminal and a peaking-power-output-terminal, wherein: the peaking-power-input-terminal is connected to the peaking-splitter-output-terminal; and the peaking-power-output-terminal is configured to provide a peaking-power-amplifier-output-signal. The splitter, the main-power-amplifier and the peaking-power-amplifier are provided by means of an integrated circuit.

A power amplifier module includes a first substrate and a second substrate, at least part of the second substrate being disposed in a region overlapping the first substrate. The second substrate includes a first amplifier circuit and a second amplifier circuit. The first substrate includes a first transformer including a primary winding having a first end and a second end and a secondary winding having a first end and a second end; a second transformer including a primary winding having a first end and a second end and a secondary winding having a first end and a second end; and multiple first conductors disposed in a row between the first transformer and the second transformer, each of the multiple first conductors extending from the wiring layer on a first main surface to the wiring layer on a second main surface of the substrate.

A balun includes: first wiring that has a first end connected to a first balanced line and a second end connected to a second balanced line; second wiring that has a grounded first end and a second end; third wiring that has a first end connected to the second end of the second wiring and a second end connected to an unbalanced line and is electromagnetically coupled to the second wiring; a first capacitor that has a first end connected to the first end of the third wiring and a grounded second end; and a second capacitor that has a first end connected to the second end of the third wiring and a grounded second end. The first wiring is electromagnetically coupled to at least one of the second wiring and the third wiring.

An apparatus includes a transformer including a first inductor, a second inductor, and a third inductor. The apparatus also includes a power amplifier having an output coupled to the first inductor, a low-noise amplifier having an input coupled to a first terminal of the third inductor, and a fourth inductor having a first terminal and a second terminal, wherein the second terminal of the fourth inductor is coupled to a second terminal of the third inductor. The apparatus also includes a switch coupled between the first terminal of the third inductor and the first terminal of the fourth inductor.

A power amplifier comprising: a first amplifier; a second amplifier, wherein the first and second amplifiers are arranged in parallel; an analogue pre-distortion network; a first coupler; and a second coupler, wherein the first coupler is configured to receive an input signal, direct said input signal to the first amplifier, and direct a first pre-distortion signal to the analogue pre-distortion network, wherein the first pre-distortion signal comprises a first distortion component generated at the input of the first amplifier, and the analogue pre-distortion network is configured to receive the first pre-distortion signal and manipulate its amplitude and/or phase to obtain a manipulated first pre-distortion signal, and the second coupler is configured to direct the manipulated first pre-distortion signal to the second amplifier.

Front end systems and related devices, integrated circuits, modules, and methods are disclosed. One such front end system includes a low noise amplifier in a receive path and a multi-mode power amplifier circuit in a transmit path. An overload protection circuit can adjust an impedance of a switch coupled to the low noise amplifier based on a signal level of the low noise amplifier. The multi-mode power amplifier circuit includes a stacked output stage including a transistor stack of two or more transistors. The multi-mode power amplifier circuit also includes a bias circuit configured to control a bias of at least one transistor of the transistor stack based on a mode of the multi-mode power amplifier circuit. Other embodiments of front end systems are disclosed, along with related devices, integrated circuits, modules, methods, and components thereof.

Low noise amplifiers (LNAs) are disclosed herein. In certain embodiments, an LNA includes an input balun configured to convert a single-ended radio frequency (RF) receive signal to a differential RF receive signal, an amplifier chain configured to amplify the differential RF receive signal to generate a differential amplified RF receive signal, and an output balun configured to convert the differential amplified RF receive signal into a single-ended amplified RF receive signal. The LNA's amplifier chain is operable in multiple gain modes, and includes a first differential amplification stage, a second differential amplification stage, and a third differential amplification stage.

A power amplifier comprises a first transistor, a first transformer, a first variable resistor, a first bias circuit and coupling circuitry configured to couple the first transformer, a first end of the first variable resistor, and a collector of the first transistor at a first node, the first transformer and a second end of the first variable resistor at a second node, and the bias circuit and a base of the first transistor at a third node.