Abstract: A bias circuit includes: a first transistor having an emitter or a source which supplies a bias to an amplifier operating by a power source voltage through a first resistive element and a base or a gate; a first capacitor having a first end electrically connected to the base or the gate of the first transistor and a second end connected to a ground; and a second transistor having a collector or a drain electrically connected to the base or the gate of the first transistor, a base or a gate electrically connected to the base or the gate of the first transistor, and an emitter or a source connected to a node which is supplied with a signal with experience of being amplified by the amplifier and the power source voltage.

Abstract: A differential amplifier circuit includes a first and second amplifiers that output a differential signal in a radio-frequency band, a first inductor having a first end connected to an output end of the first amplifier, a second inductor having a first end connected to an output end of the second amplifier, a choke inductor connected to second ends of the first and second inductors, a first and second capacitors, and a switch that connects the second capacitor in parallel to the first capacitor or terminates a parallel connection of the first and second capacitors. A resonant circuit formed by connecting the first or second inductor in series with the first capacitor has a different resonant frequency from a resonant circuit formed by connecting the first or second inductor in series with the parallel-connected first and second capacitors. These resonant frequencies correspond to second harmonic frequencies of the differential signal.

Abstract: A power amplifier circuit has an input node from which an input signal, which is a high-frequency signal, is inputted and an output node to which the input signal is amplified by a differential amplifier circuit to be outputted as an output signal. The power amplifier circuit includes a balun transformer (second balun transformer) including an input-side winding that has a substantially center to which a power-supply voltage is supplied and that is connected between differential outputs of the differential amplifier circuit, and an output-side winding that is coupled to the input-side winding via an electromagnetic field and that has one end connected to a reference potential; and a capacitive element (capacitor) provided between another end (node) of the output-side winding and the output node.

Abstract: A power amplifier circuit includes a first amplifier that operates in accordance with a first voltage supplied from a voltage supply source, amplifies a first signal, and outputs an amplification signal, a bias transistor that includes a base or a gate to which a bias control current is supplied and an emitter or a source supplying a bias to the first amplifier through a first resistor element, and a protection circuit that causes part of the bias control current to flow to a ground on the basis of the amplification signal and a second signal based on the first voltage.

Abstract: A power amplifier circuit includes a first amplification element having an output terminal and amplifying a harmonic signal input to an input terminal, a second amplification element having an output terminal and amplifying a harmonic signal input to an input terminal, a bias circuit that supplies a bias to each of the input terminal of the first amplification element and the second amplification element, a first resistance element electrically connected to the output terminal of the first amplification element, and a second resistance element electrically connected to the output terminal of the second amplification element and electrically connected to the other end of the first resistance element in series, the bias circuit is electrically connected to a connection point in a portion in which the other end of the first resistance element and the other end of the second resistance element are electrically connected in series.

Abstract: A power amplifier circuit includes a first transistor configured to receive a first signal at a base, amplify the first signal, and output a second signal from a collector; and a bias circuit configured to supply a bias current to the base of the first transistor. The bias circuit includes a second transistor configured to supply a bias current to the base of the first transistor, a third transistor including a base connected to a base of the second transistor and a collector connected to a collector of the second transistor, and a fourth transistor including a base connected to an emitter of the third transistor and a collector connected to an emitter of the second transistor and configured to draw at least part of the bias current.

Abstract: A power amplifier circuit includes a power splitter, a first amplifier configured to output a first amplified signal from a first output terminal, and a second amplifier configured to output a second amplified signal from a second output terminal. The power amplifier circuit further includes a first termination circuit connected between the first output terminal and the second output terminal, a first transmission line, a second transmission line, a second termination circuit connected between another end of the first transmission line and another end of the second transmission line, and a power combiner.

Abstract: A matching circuit includes: a first wire having one end connected to a first terminal and another end; a second wire having one end connected to the other end of the first wire and another end connected to a first reference potential and electromagnetically coupled to the first wire; and a third wire having one end connected to the one end of the second wire and another end connected to a second terminal and electromagnetically coupled to at least one of the first wire and the second wire.

Abstract: A power amplifier circuit includes an amplifier transistor having a base, a collector, a bias circuit, and a first resistance element connected between the base of the amplifier transistor and the bias circuit. The bias circuit includes a voltage generation circuit, a first transistor having a base to which a first direct-current voltage is supplied, and an emitter from which the bias current or voltage is supplied, a second transistor having a base to which a second direct-current voltage is supplied, and an emitter connected to the emitter of the first transistor, a signal supply circuit disposed between the base of the amplifier transistor and the base of the second transistor, and an impedance circuit disposed between the base of the first transistor and the base of the second transistor.

Abstract: 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.

Abstract: The present disclosure provides a power amplifier circuit capable of suppressing the occurrence of noises while enabling control of an output power level. The power amplifier circuit includes a first transistor that amplifies a first signal; a bias circuit that supplies a bias current or voltage based on a control signal to the first transistor; a second transistor to which a control current based on the control signal is supplied, which has an emitter or a source thereof connected to a collector or a drain of the first transistor, and from which a second signal obtained by amplifying the first signal is output; and a first feedback circuit provided between the collector or the drain of the second transistor and the base or the gate of the second transistor.

Abstract: A power amplifier circuit includes an amplifier transistor, a bias circuit that supplies a bias current or voltage to the amplifier transistor, and a resistance element connected between a base of the amplifier transistor and the bias circuit. The bias circuit includes a voltage generation circuit, a first transistor having a base to which a first direct-current voltage is supplied and an emitter from which the bias current or voltage is supplied, a second transistor having a base to which a second direct-current voltage is supplied and an emitter connected to the emitter of the first transistor, a signal supply circuit that supplies an input signal to the base of the second transistor, and an impedance circuit disposed between the base of the first transistor and the base of the second transistor.

Abstract: A power amplifier includes power amplification circuits in a plurality of stages including a first stage and a second stage, each power amplification circuit including a transistor. The power amplification circuit in the first stage includes a first impedance circuit between an emitter of the transistor and a reference potential. The first impedance circuit has an impedance that does not vary with frequency or an impedance that varies with frequency. The power amplification circuit in the second stage includes a second impedance circuit between an emitter of the transistor and a reference potential. The second impedance circuit has an impedance that does not vary with frequency or an impedance that varies with frequency.

Abstract: A power amplifier circuit includes a first transistor having the base coupled to an input terminal, the collector coupled to an output terminal, and the emitter coupled to ground, a first bias circuit coupled to the base of the first transistor via the first resistance element, a second transistor having the base coupled to the input terminal, the collector coupled to the output terminal, and the emitter coupled to ground, a second bias circuit coupled to the base of the second transistor via the second resistance element, and a first impedance circuit having a first end coupled between the base of the first transistor and the input terminal and a second end coupled between the first bias circuit and the first resistance element and being configured to be opened for a direct-current component and to be closed for an alternating-current component.

Abstract: A differential amplification circuit includes a differential amplifier configured to output a signal including harmonics and first and second filters configured to reduce level of an even harmonic included in output from the differential amplifier. The first and second filters are connected to output of the differential amplifier. The first filter includes a resonant circuit composed of a capacitor and an inductor and a resonant circuit composed of a capacitor and the inductor. The second filter includes a resonant circuit composed of a capacitor and an inductor and a resonant circuit composed of a capacitor and the inductor. A center frequency of the first filter is lower than a center frequency of the even harmonic. A center frequency of the second filter is higher than the center frequency of the even harmonic.

Abstract: A power amplifier circuit includes a differential amplifier circuit configured to amplify a radio-frequency signal, a transformer disposed on an output side with respect to the differential amplifier circuit and including a primary winding and a secondary winding, and a dispersion circuit coupled to a midpoint of the primary winding of the transformer and configured to operate as an adjustment circuit. The dispersion circuit is configured to adjust, based on a supply voltage controlled in accordance with the envelope of the radio-frequency signal, a bias (bias current or bias voltage) to be supplied to the differential amplifier circuit.

Abstract: A power amplifier circuit includes a first path and a second path between an input terminal and an output terminal, a first amplifier located in the first path operative in a first mode, a second amplifier located in the second path operative in a second mode, a first matching circuit between the first amplifier and the output terminal in the first path, a first capacitor having a first end connected to the output terminal side of the first matching circuit, and a second end, a first inductor having a first end connected to the second end of the first capacitor and a second end grounded, and a short-circuit switch connected in parallel with the first inductor. The short-circuit switch short-circuits the first and second ends of the first inductor in the first mode and is placed in an open-circuit position in the second mode.

Abstract: A power amplifying circuit includes a first amplifier, a second amplifier, a transformer having a primary winding and a secondary winding, and a capacitor. The first amplifier amplifies a signal which is one of differential signals. The second amplifier amplifies a signal which is the other of the differential signals. The primary winding is connected, at its first end, to the first amplifier, and is connected, at its second end, to the second amplifier. The secondary winding is connected, at its first end, to an unbalanced line through which an unbalanced signal is transmitted, and is connected, at its second end, to the ground. The secondary winding is electromagnetically coupled to the primary winding. The capacitor is connected, at its first end, to the midpoint of the primary winding, and is connected, at its second end, to the ground.

Abstract: A power amplifier circuit includes: a high pass filter that has one end into which a high frequency input signal is inputted; a first amplifier that amplifies the high frequency input signal outputted from the other end of the high pass filter and outputs a high frequency signal obtained through the first amplification; a second amplifier that amplifies the high frequency signal and outputs a high frequency output signal obtained through the second amplification; an automatic transformer that performs impedance matching between the first amplifier and the second amplifier; and an impedance circuit, one end of which is electrically connected with the other end of the high pass filter, the other end of which is electrically connected with an output terminal of a bias circuit outputting bias voltage or bias current to the first amplifier, and that outputs the high frequency input signal to the bias circuit.

Abstract: A power amplifier circuit includes a first transistor, a second transistor, a first bias circuit supplying a first bias current or voltage, a second bias circuit supplying a second bias current or voltage, a first inductor, and a first capacitor. A power supply voltage is supplied to a collector of the first transistor, and an emitter thereof is grounded. A radio frequency signal and the first bias current or voltage are supplied to a base of the first transistor. The power supply voltage is supplied to a collector of the second transistor, and an emitter thereof is connected to the collector of the first transistor via the first capacitor and is grounded via the first inductor. The second bias current or voltage is supplied to a base of the second transistor. An amplified radio frequency signal is output from the collector of the second transistor.