A power amplifier has improved power added efficiency at high output power. The power amplifier includes: a first transistor for amplifying an input signal input to the base thereof and outputting the amplified signal from the collector thereof; a second transistor with power-supply voltage applied to the collector thereof to supply bias voltage or bias current from the emitter thereof to the base of the first transistor; a third transistor whose collector is connected to the collector of the first transistor to amplify the input signal input to the base thereof and output the amplified signal from a collector thereof; a fourth transistor whose base and collector are connected to supply bias from the emitter thereof to the base of the third transistor; and a first resistor with bias control voltage applied to one end thereof and the other end connected to the bases of the second and fourth transistors.

A Doherty amplifier includes: a carrier amplifier that is formed on a semiconductor substrate and that includes amplifiers in one or more stages including a first amplifier in one stage to which a first bias current is inputted; a peak amplifier that is formed on the semiconductor substrate and that includes amplifiers in two or more stages including a second amplifier to which a second bias current smaller than the first bias current is inputted; and a first resistor that is inserted in series into a power supply path to the second amplifier.

A power amplifier cell is disclosed having a first transistor with a first terminal coupled to ground, a second terminal, and a first control terminal. A second transistor has a third terminal coupled to the second terminal, a fourth terminal, and a second control terminal. Further included is a capacitor having a first plate coupled directly to the second control terminal and a second plate coupled to the ground. As such, there is no intervening inductor component coupled between the first plate and the second control terminal, leaving only parasitic inductance between the first plate and the second control terminal. The capacitor has a capacitance sized to resonate with the parasitic inductance at a resonant frequency substantially higher than a desired frequency of operation of the power amplifier cell.

A power amplifier configured to amplify an input radio-frequency (RF) signal includes a first power transistor including an input terminal; a first capacitor having a first end connected to the input terminal of the first power transistor; and a resistor having a first end connected to a second end of the first capacitor and a second end connected to a ground. The input RF signal is input to the second end of the first capacitor and the first end of the resistor.

A power amplifier includes: plural amplifiers; a tournament-tree-shaped circuit connected with the plural amplifiers and including plural transmission lines arranged in a tournament-tree shape; and plural difference frequency short circuits shunt-connected with plural nodes of the tournament-tree-shaped circuit, wherein each of the plural difference frequency short circuits includes an inductor and a capacitor connected in series, resonant frequencies of the plural difference frequency short circuits become lower as the plural difference frequency short circuits are more separated from the plural amplifiers, and the difference frequency short circuits having equivalent resonant frequencies are connected with plural nodes in the same stage among the plural nodes.

A dual amplifier apparatus is disclosed. The apparatus includes an energy module having a controller and a first and second power amplifier circuit coupled to the controller. The first and second power amplifier circuits are configured to receive and amplify an input signal to generate a first output signal into a load coupled to the output of the first and second power amplifier circuit. A power rating of the first amplifier circuit is different from a power rating of the second amplifier circuit. The controller is configured to select the first or the second power amplifier circuit.

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.

A scalable periphery tunable matching power amplifier is presented. Varying power levels can be accommodated by selectively activating or deactivating unit cells of which the scalable periphery tunable matching power amplifier is comprised. Tunable matching allows individual unit cells to see a constant output impedance, reducing need for transforming a low impedance up to a system impedance and attendant power loss. The scalable periphery tunable matching power amplifier can also be tuned for different operating conditions such as different frequencies of operation or different modes.

An electromagnetic induction heating apparatus for heating an aerosol-forming article of an electronic cigarette includes: a power supply unit configured to supply DC power; a power amplifier including a switch unit comprising a pair of transistor switches having a differential structure and receiving DC power from the power supply unit, and a parallel-structured LC resonant network including a resonant inductor connected to an output terminal of the switch unit and electromagnetically inductively coupled with an inductor component of a heat-generating body for heating the aerosol-forming article of the electronic cigarette, and a resonant capacitor connected in parallel to the resonant inductor; and a driving unit configured to adjust a temperature of the heat-generating body by adjusting an operating frequency of the switch unit of the power amplifier to control an amount of current of the resonant inductor electromagnetically inductively coupled with the inductor component of the heat-generating body.

A power amplifier circuit includes a first amplifier, a second amplifier, and, an output terminal. The power amplifier circuit includes an impedance conversion unit connected to an output end of one amplifier, which is either the first amplifier or the second amplifier. The impedance conversion unit includes a first line with one end connected to the output end, a second line with one end connected to another end of the first line, and a first capacitor with one end connected to a connection point between the first line and the second line and with another end connected to a reference potential. The first line and the second line are coupled to each other. A signal based on a connection point between an output end of another amplifier of the first amplifier and the second amplifier and another end of the second line is outputted from the output terminal.