Abstract: The present invention relates to a high-frequency switching circuit, and provides a high-frequency switching circuit capable of withstanding high output power, achieving highly efficient isolation, and reducing an insertion loss using inexpensive pin diodes. A switching control voltage or ground voltage developed at one power supply is applied to a control terminal. A diode resonant circuit includes a diode that applies a signal to an output terminal through an anode thereof and a signal to an input terminal through a cathode thereof, and has a resonant circuit, which attains a parallel resonance owing to a parasitic capacitance formed when the diode is off in the frequency band of the high-frequency signal, interposed between the anode and cathode of the diode. A first bias circuit separates a switching control current stemming from the switching control voltage applied to the control terminal from the high-frequency signal and supplies the switching control current to the anode of the diode.

Abstract: A transistor bias circuit which achieves stable operation in a multistage-connected amplifier circuit or in a compound circuit is formed, for example, by a transistor amplifier and a mixer. The transistor bias circuit, which establishes the operating point of a transistor, has an input biasing circuit which is connected to a signal input terminal of the transistor and which applies a bias current to this input terminal from a power supply. The input biasing circuit has an input frequency selection unit which passes an AC input signal input to the transistor signals input terminal within a prescribed frequency band, and which attenuates an AC input signal input to the transistor signal input terminal outside the prescribed frequency band.