Abstract: A T/R switch applicable to an ultrasonograph and capable of transmitting a signal reflected from a living body over a wide band with low noise without causing erroneous operation of the switch or element destruction even when the potential of a transmission signal or reflected signal changes includes: a common source terminal commonly and serially coupling the source terminals of two MOS transistors; a common gate terminal commonly coupling the gate terminals of the two MOS transistors; a main switch, the drain terminals of which are connected to input/output terminals; and a floating voltage circuit which is connected to the common gate terminal and common source terminal, makes the common gate terminal potential follow, in phase, variation in the common source terminal potential, and sends a signal to turn the switch on or off to the common gate terminal.

Abstract: A T/R switch applicable to an ultrasonograph and capable of transmitting a signal reflected from a living body over a wide band with low noise without causing erroneous operation of the switch or element destruction even when the potential of a transmission signal or reflected signal changes includes: a common source terminal commonly and serially coupling the source terminals of two MOS transistors; a common gate terminal commonly coupling the gate terminals of the two MOS transistors; a main switch, the drain terminals of which are connected to input/output terminals; and a floating voltage circuit which is connected to the common gate terminal and common source terminal, makes the common gate terminal potential follow, in phase, variation in the common source terminal potential, and sends a signal to turn the switch on or off to the common gate terminal.