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.