Abstract: An amplifier device includes an amplifier including cascade-connected power amplifiers in a plurality of stages and a bias circuit configured to supply bias currents to the amplifier. A bias current supplied to a power amplifier in the first stage of the power amplifiers in the plurality of stages exhibits a positive temperature characteristic. A bias current supplied to a power amplifier in the final stage exhibits a negative temperature characteristic.

Abstract: A transmission circuit appropriately controls output power in response to fluctuations in the impedance of a load. A transmission circuit includes: a transistor to which a bias current IB1 is supplied and that amplifies and outputs an input signal RFin; a transistor to which a bias current IB2 is supplied, that has a collector connected to the collector of the transistor, and that amplifies and outputs the input signal; a current generation circuit that generates a current I2 on the basis of a current I1 from the emitter of the transistor; and a bias control circuit that outputs a first bias control signal for controlling the bias current IB1 and a second bias control signal for controlling the bias current IB2 on the basis of the current I2.

Abstract: A power amplifier circuit includes: a transistor which is supplied at a base with a bias current, amplifies an input signal, and outputs a current; a transistor which is connected at a base to the base of the transistor and in which a current commensurate with the current is input to a collector; a transistor which outputs a bias control signal which controls supply of the bias current; and a control circuit which is connected to the collector of the transistor and a gate of the transistor and controls a bias control signal on the basis of a reference current based on a reference signal and the current.

Abstract: An amplifier device includes an amplifier including cascade-connected power amplifiers in a plurality of stages and a bias circuit configured to supply bias currents to the amplifier. A bias current supplied to a power amplifier in the first stage of the power amplifiers in the plurality of stages exhibits a positive temperature characteristic. A bias current supplied to a power amplifier in the final stage exhibits a negative temperature characteristic.