JPH05291920

PURPOSE:To enhance an isolation with a simple circuit and to eliminate a need for a negative power supply by providing a switching means turning on/off a power supply to a buffer amplifier and giving a forward bias to a diode to the switch circuit. CONSTITUTION:A voltage equal to a power supply voltage is applied to an anode of a diode 9 attended with the turning on of a switching transistor(TR) 7. Moreover, when a control voltage fed to a base of the TR 7 is high, since the TR7 is turned on, a buffer amplifier 1 is turned off and an anode potential of the diode is lost, then a reverse bias is applied to diodes 9,10, which are turned off. As a result, a high frequency signal inputted to the amplifier 1 is interrupted by the amplifier 1 and the diode and no output appears at an output terminal 15.