A power amplifier circuit includes a first transistor having a first terminal to which a voltage corresponding to a variable power supply voltage is to be supplied and a second terminal to which a radio-frequency signal is to be supplied, the first transistor being configured to amplify the radio-frequency signal, a bias circuit configured to supply a bias current or voltage to the second terminal of the first transistor, and an adjustment circuit configured to adjust the bias current or voltage in accordance with the variable power supply voltage supplied from a power supply terminal.

A duplexer may be used to isolate a transmitter and a receiver that share a common antenna. By using impedance gradients to provide impedances that cause balance-unbalance transformers (balun) of the duplexer to cut-off access to the common antenna rather than duplicate the antenna impedance, the duplexer is balanced. Such cut-offs may have a lower insertion loss than a duplexer that merely duplicates the antenna impedance to separate the differential signals of the receiver and transmitter from the common mode signal.

A duplexer may be used to isolate a transmitter and a receiver that share a common antenna. By using impedance gradients to provide impedances that cause balance-unbalance transformers (balun) of the duplexer to cut-off access to the common antenna rather than duplicate the antenna impedance, the duplexer is balanced. Such cut-offs may have a lower insertion loss than a duplexer that merely duplicates the antenna impedance to separate the differential signals of the receiver and transmitter from the common mode signal.

A receiver front end having low noise amplifiers (LNAs) is disclosed herein. A cascode having a “common source” configured input FET and a “common gate” configured output FET can be turned on or off using the gate of the output FET. A first switch is provided that allows a connection to be either established or broken between the source terminal of the input FET of each LNA. A drain switch is provided between the drain terminals of input FETs to place the input FETs in parallel. This increases the g.sub.m of the input stage of the amplifier, thus improving the noise figure of the amplifier.

A receiver front end having low noise amplifiers (LNAs) is disclosed herein. A cascode having a “common source” configured input FET and a “common gate” configured output FET can be turned on or off using the gate of the output FET. A first switch is provided that allows a connection to be either established or broken between the source terminal of the input FET of each LNA. A drain switch is provided between the drain terminals of input FETs to place the input FETs in parallel. This increases the g.sub.m of the input stage of the amplifier, thus improving the noise figure of the amplifier.

A transmission/reception module includes a substrate including a transmission signal input terminal, a reception signal output terminal, and an antenna terminal, an antenna switch circuit provided on the substrate and configured to output a transmission signal input from the transmission signal input terminal to the antenna terminal and configured to output a reception signal input from the antenna terminal to the reception signal output terminal, and a first inductor included in an input/output filter circuit provided between the antenna switch circuit and the antenna terminal. The first inductor includes a conductor whose winding axis direction is orthogonal to the substrate.

A power amplifier circuit includes: an amplifier that amplifies an input signal; and a resonant circuit that is connected to an output terminal of the amplifier and that attenuates a harmonic wave of an amplified signal obtained by amplifying the input signal. The resonant circuit includes an inductor disposed between the amplifier and a ground, a capacitive element disposed between the amplifier and the ground and connected in series to the inductor, an inductor connected in parallel to the inductor, a switch connected in series to the inductor, and a switch that is connected in parallel to the switch and that is of an element size common to an element size of the switch.

A power amplifier circuit includes an amplifier that amplifies an input signal RFin, a matching circuit that provides impedance matching between an output port of the amplifier and an output terminal, an input of the matching circuit being connected to the output port of the amplifier, an output of the matching circuit being connected to the output terminal, and a resonant circuit provided between ground and a signal path that connects the output port of the amplifier and the input of the matching circuit, the resonant circuit resonating at a resonant frequency greater than or equal to the frequency of a fourth harmonic wave of an amplified signal obtained by amplifying the input signal.

A power amplifier circuit includes an amplifier that amplifies an input signal RFin, a matching circuit that provides impedance matching between an output port of the amplifier and an output terminal, an input of the matching circuit being connected to the output port of the amplifier, an output of the matching circuit being connected to the output terminal, and a resonant circuit provided between ground and a signal path that connects the output port of the amplifier and the input of the matching circuit, the resonant circuit resonating at a resonant frequency greater than or equal to the frequency of a fourth harmonic wave of an amplified signal obtained by amplifying the input signal.

A reactance cancelling radio frequency (RF) circuit array is disclosed. The reactance cancelling RF circuit array includes multiple RF circuits each coupled to one or two adjacent RF circuits by one or two pairs of coupling mediums each having a respective length less than one-quarter wavelength. In one aspect, an RF input signal is first split across the RF circuits and then combined to form an RF output signal. As a result, each RF circuit requires a lower power handling capability to process a portion of the RF input signal. In another aspect, each pair of the coupling mediums can cause reactance cancellation in each reactance-cancelling pair of the RF circuits. By coupling the RF circuits via the coupling mediums and enabling splitting-combining among the RF circuits, it is possible to miniaturize the reactance cancelling RF circuit array for improved performance across a wide frequency spectrum.