Patent ID: 7161197

Claim:
An RF switching circuit, comprising: a plurality of input/output terminals for inputting and outputting an RF signal; a switch for opening and closing an electrical connection between the input/output terminals, and a control line, wherein the switch is constituted by a multi-gate field effect transistor including a plurality of gates located between source and drain spaced from each other on a semiconductor layer, the number of said input/output terminals is three, the RF switching circuit is an SPDT RF switching circuit including two said multi-gate field effect transistors each connected between each two of the input/output terminals, a bias voltage is applied to an inter-gate region of the semiconductor layer between the gates, the bias voltage is equal to or lower than 90% of a high-level voltage, which is a voltage for turning the multi-gate field effect transistor ON, in a state where the multi-gate field effect transistor is ON, and is equal to or higher than 80% of the high-level voltage and equal to or lower than the high-level voltage in a state where the multi-gate field effect transistor is OFF, and the control line is connected between the gates of one of the multi-gate field effect transistors and the inter-gate region of the other multi-gate field effect transistor.