Design of the Doherty amplifier with push-pull structure using balun transformer

Push-pull structure with balun transformer is presented as load modulation technique which improves the overall efficiency of power amplifier. Under the assumption that output impedance of turned-off amplifier is high, conventional Doherty amplifier is composed of impedance inverter and additional peaking amplifier. In many case, however, output impedance of ´off´ amplifier is very low due to matching network or parasitic output capacitance. This paper introduces novel load modulation technique with push-pull structure which uses low impedance characteristic of off amplifier. Experimental results show that efficiency enhancement and good linearity of the proposed structure. To the authors´ knowledge this is the first experimental results with a push-pull structure Doherty amplifier.