Rf power amplifier system having amplifier protection

Abstract

An RF power amplifier having improved amplifier protection. An RF source provides an RF signal to be amplified. The amplifier includes a bridge circuit having an input circuit adapted for connection across a DC voltage source and an output circuit connected across a load. The bridge circuit includes first and second transistors for, when on, connecting the DC voltage source across the load for DC current flow therethrough in a first direction and third and fourth transistors for, when on, connecting the DC voltage source across the load for DC current flow therethrough in a second direction. The transistors are controlled in response to the RF signal so that they turn on and off at a frequency dependent upon that of the RF signal and such that current flows from the DC source alternately in the first and second directions through the load. An amplifier control serves to apply a reverse bias to the second and fourth transistors to prevent them from conducting current until receipt of a turn on signal. The turn on signal is provided for actuating the amplifier controller to remove the reverse bias from the second and fourth transistors such that the reverse bias applied to the fourth transistor is removed during a first half cycle of the RF signal when the fourth transistor is off and that the reverse bias applied to the second transistor is removed during a succeeding half cycle when the second transistor is off.