A composite power amplifier for amplification of an input signal into an output signal is disclosed. The composite power amplifier comprises an input port for receiving the input signal, and an output port for providing the output signal. Furthermore, the composite power amplifier comprises a first set of sub-amplifiers, comprising at least two sub-amplifiers, wherein the at least two sub-amplifiers are arranged along a taper of a first transmission line, wherein the first transmission line is connected to the first set of sub-amplifiers and the output port. Moreover, the composite power amplifier comprises a second set of sub-amplifiers, comprising at least two sub-amplifiers, wherein the at least two sub-amplifiers are arranged along a taper of a second transmission line, wherein the second transmission line is connected to the second set of sub-amplifiers and the output port.

A current compensation circuit for providing a current to an amplifier circuit includes a first amplifier, a first transistor and a first bias circuit. The first bias circuit provides a first bias current to the first amplifier. The current compensation circuit includes a power detection circuit, an operational amplifier circuit and a current-to-voltage converter. The power detection circuit detects and converts an input power or an output power of the first amplifier to a first detection voltage. The operational amplifier circuit generates a second detection voltage according to the first detection voltage and a calibration voltage. The current-to-voltage converter converts the second detection voltage to a compensation current. A first compensation current flows to the first amplifier through the first transistor according to the compensation current, such that the first amplifier is driven by the first bias current plus the first compensation current.

An output network connected to an output of a nonlinear unmatched power amplifier that provides an amplified voltage signal at a fundamental frequency. The output network includes multiple acoustic resonators configured to match multiple harmonic frequencies of the amplified voltage signal to one of substantially zero impedance, appearing as a short, or substantially infinite impedance, appearing as an open, resulting in zero voltage or zero current, respectively, to avoid power distribution at the higher harmonic frequencies. Each higher harmonic frequency is higher than a first harmonic frequency of the multiple harmonic frequencies, which is a fundamental frequency.

An output network connected to an output of a nonlinear unmatched power amplifier that provides an amplified voltage signal at a fundamental frequency. The output network includes multiple acoustic resonators configured to match multiple harmonic frequencies of the amplified voltage signal to one of substantially zero impedance, appearing as a short, or substantially infinite impedance, appearing as an open, resulting in zero voltage or zero current, respectively, to avoid power distribution at the higher harmonic frequencies. Each higher harmonic frequency is higher than a first harmonic frequency of the multiple harmonic frequencies, which is a fundamental frequency.

An output network connected to an output of a nonlinear unmatched power amplifier that provides an amplified voltage signal at a fundamental frequency. The output network includes multiple acoustic resonators configured to match multiple harmonic frequencies of the amplified voltage signal to one of substantially zero impedance, appearing as a short, or substantially infinite impedance, appearing as an open, resulting in zero voltage or zero current, respectively, to avoid power distribution at the higher harmonic frequencies. Each higher harmonic frequency is higher than a first harmonic frequency of the multiple harmonic frequencies, which is a fundamental frequency.

An output network connected to an output of a nonlinear unmatched power amplifier that provides an amplified voltage signal at a fundamental frequency. The output network includes multiple acoustic resonators configured to match multiple harmonic frequencies of the amplified voltage signal to one of substantially zero impedance, appearing as a short, or substantially infinite impedance, appearing as an open, resulting in zero voltage or zero current, respectively, to avoid power distribution at the higher harmonic frequencies. Each higher harmonic frequency is higher than a first harmonic frequency of the multiple harmonic frequencies, which is a fundamental frequency.

Multiband power amplifier with cascode switching. A power amplification system can include a first transistor having a base configured to receive an input radio-frequency (RF) signal and having an emitter coupled to a ground potential. The power amplification system can include a plurality of second transistors. Each one of the plurality of second transistors can have a respective emitter coupled to a collector of the first transistor and can be configured to, when biased at a respective base, output an output RF signal at a respective collector. The power amplification system can further include a biasing circuit configured to bias one or more of the plurality of second transistors based on a control signal.

Multiband power amplifier with cascode switching. A power amplification system can include a first transistor having a base configured to receive an input radio-frequency (RF) signal and having an emitter coupled to a ground potential. The power amplification system can include a plurality of second transistors. Each one of the plurality of second transistors can have a respective emitter coupled to a collector of the first transistor and can be configured to, when biased at a respective base, output an output RF signal at a respective collector. The power amplification system can further include a biasing circuit configured to bias one or more of the plurality of second transistors based on a control signal.

A ultra-compact coupler designed to sample the actual output power of a power amplifier and which is VSWR insensitive, such that reflected power is essentially not coupled to a detector circuit and only forward power is detected and processed. In a first embodiment, a coupler is situated between the final amplifier stage of a power amplifier and an output impedance matching network, and is specially configured for operation in a low impedance environment in conjunction with a detector circuit, thereby substantially reducing the areal size of the coupler. In a second embodiment, a coupler is integrated within an output impedance matching network coupled to the final amplifier stage of a power amplifier so as to share an inductor between the coupler and the output impedance matching network, thereby further substantially reducing the areal size of the coupler.

Certain aspects of the present disclosure provide methods and apparatus for current-limiting protection of an amplifier, such as a power amplifier in a radio frequency (RF) front-end. One example current-limiting circuit generally includes a node coupled to a current source, a plurality of current-sinking devices coupled to the node, one or more switches coupled between the node and at least one of the plurality of current-sinking devices, and a bias circuit having an input coupled to the node and an output for coupling to an input of the amplifier.