Abstract: An amplifier having a first transistor with an output coupled to a common output node and a switch for coupling a control electrode of the first transistor to a first bias source to bias such first transistor to a conducting state during a relatively high power operating mode or for removing such control electrode from the first bias source to place the first transistor in a non-conducting condition during a relatively low power operating mode selectively in accordance with a control signal. A second transistor has an output coupled to the common output node and a second bias source coupled to a control electrode to the second transistor to bias such second transistor to a conducting state during both the relatively high power operating mode and the relatively low power operating mode.

Abstract: An RF power amplifier for delivering power to a load including a first quadrature hybrid coupler driving two class C amplifiers operating with high input compression, a second quadrature hybrid coupler coupled to the outputs of the amplifiers, an attenuator, and a phase shifter. An impedance mismatch by the load causes phase-pulling of the amplifiers which reduces output to the load. This is compensated for by feeding an error signal, indicating the magnitude and phase of the phase-pulling of the two amplifiers, from the second quadrature hybrid coupler through the attenuator and the phase shifter back to the first quadrature hybrid coupler. The attenuated and phase shifted error signal adds to or is subtracted from the input signals to the two amplifiers. Therefore, one of the two amplifiers is driven with more signal and the other amplifier is driven with less signal to phase-push the two amplifiers to compensate for the phase-pulling to thereby increase the output to the load.