Abstract: Efficiency of an RF/microwave power amplifier is increased at a back-off power level by increasing the load resistance of the amplifier at the reduced output power level as compared to load impedance at a higher power level including full operating power. The different load impedances can be realized with two amplification units in parallel each having different load impedances. Alternatively, a single amplification path can be provided with an output impedance matching network which is selectively bypassed for increased impedance load during back-off power operation. In another embodiment, the output impedance matching network can include a shunt inductance which is selectively switched into the network to increase impedance for back-off power operation.

Abstract: An RF microwave power transistor has an input/output feed structure which functions as a low impedance microstrip line by providing a ground plane in close proximity to the feed structure on one surface of a semiconductor body. A second ground plane can be provided on an opposing surface of the semiconductor body with vias interconnecting the first and second ground planes. In addition to reducing feed impedance, a larger total transistor size can be provided before “odd mode oscillation” occurs.

Abstract: In an RF amplifier circuit having a plurality of transistor stages with each transistor having an input terminal for receiving an RF signal, a bias circuit is provided for applying a DC bias to the input terminal of a transistor. An isolation circuit connects a DC power supply to a bias circuit whereby DC voltage from the power terminal is applied to the bias circuit and RF signal from the transistor input terminal is attenuated. The isolation circuit includes a reactive serial path which allows the flow of DC current and presents an impedance to RF current flow and a reactive shunt path to ground which can comprise a capacitor or a serial inductor/capacitor circuit. The reactive serial path can comprise an inductor or an inductor/capacitor parallel circuit.