Abstract: A semiconductor device and a radio frequency circuit which are appropriate for multiband, multimode performance can be realized as a semiconductor device including a field-effect transistor formed on a semiconductor substrate, and include: ohmic electrodes serving as source and drain electrodes of the field-effect transistor, first and second Schottky electrodes provided between the ohmic electrodes and serving as gate electrodes of the field-effect transistor, and a third Schottky electrode provided and grounded between the first and second Schottky electrodes.

Abstract: To provide a radio frequency power amplifier that realizes a favorable high-frequency characteristic without using an isolator and also achieves low power consumption. The radio frequency power amplifier includes: a power amplifier which amplifies a radio frequency signal; a voltage supplying unit which supplies a collector voltage to the power amplifier; a current supplying unit which supplies a bias current to the power amplifier; and a bias current detecting unit which detects the bias current. The voltage supplying unit has a control unit which sets the power supply voltage at: a first voltage when the detected bias current is lower than a bias-current reference value; and a second voltage lower than the first voltage when the detected bias current is higher than the bias-current reference value.

Abstract: A semiconductor device which detects a power level of a radio-frequency signal includes: a switch FET including: a semiconductor layer; a source electrode and a drain electrode; a first gate electrode; a second gate electrode formed between the first gate electrode and the drain electrode and on the semiconductor layer, each of the first gate electrode and the second gate electrode being in Schottky contact with the semiconductor layer, and the source electrode receiving the radio-frequency signal; a resistor having one end electrically connected to the first gate electrode and an other end electrically connected to the drain electrode via a capacitor; and a power detection terminal electrically connected to a connecting point between the resistor and the capacitor.

Abstract: A semiconductor device and a radio frequency circuit which are appropriate for multiband, multimode performance can be realized as a semiconductor device including a field-effect transistor formed on a semiconductor substrate, and include: ohmic electrodes serving as source and drain electrodes of the field-effect transistor, first and second Schottky electrodes provided between the ohmic electrodes and serving as gate electrodes of the field-effect transistor, and a third Schottky electrode provided and grounded between the first and second Schottky electrodes.

Abstract: A radio frequency signal is input to the bases of transistors via respective capacitors, is amplified, and is output from the collectors of the transistors. The emitter of each transistor is grounded. A bias current input from a bias circuit is supplied to the bases of the transistors via respective resistors both during low-output operation and during high-output operation. The collectors of the transistors are connected via an impedance circuit to a bias voltage input terminal. Therefore, during high-output operation, a direct current offset voltage is generated by the impedance circuit based on a portion of a radio frequency signal output from the collectors, thereby further increasing the bias current.

Abstract: In a multi-stage amplifier, a power supply circuit and a multiplier perform control so that, when there are manufacturing variations in, for example, inter-stage capacitance, a collector voltage of a stage immediately preceding a final stage is smaller than a collector voltage of the final stage, thereby suppressing variations in AM-PM characteristics.

Abstract: A radio frequency signal is input to the bases of transistors via respective capacitors, is amplified, and is output from the collectors of the transistors. The emitter of each transistor is grounded. A bias current input from a bias circuit is supplied to the bases of the transistors via respective resistors both during low-output operation and during high-output operation. The collectors of the transistors are connected via an impedance circuit to a bias voltage input terminal. Therefore, during high-output operation, a direct current offset voltage is generated by the impedance circuit based on a portion of a radio frequency signal output from the collectors, thereby further increasing the bias current.

Abstract: Provided is a matching circuit, radio-frequency power amplifier, and mobile phone whereby the second harmonic can be suppressed and the loss of fundamental due to the self resonant frequency of components can be reduced. The output matching circuit includes: a transmission line through which a radio-frequency signal is transmitted; and resonators each of which includes a capacitor. The resonators respectively have (i) first terminals connected to substantially a same connecting point on the transmission line and (ii) second terminals that are grounded.

Abstract: A radio frequency circuit according to the present invention, is a radio frequency circuit for amplifying a radio frequency signal, the radio frequency circuit comprising: an amplifier circuit for amplifying the radio frequency signal and outputting an amplified signal obtained by the amplification of the radio frequency signal; a load circuit connected to an output of the amplifier circuit; a plurality of transmission lines; a selection circuit for selecting a transmission line among the plurality of transmission lines in accordance with a predetermined parameter of the amplified signal so as to connect the selected transmission line to an output of the load circuit; and a conversion circuit for converting, into a predetermined load impedance, a load impedance looking from the amplifier circuit toward an output side of the amplifier circuit, the conversion being performed in the transmission line selected by the selection circuit.