An amplifier circuit includes a pair of amplifying devices, a first balun coupled between an input port of the amplifier circuit and RF input ports of the pair of amplifying devices and a second balun coupled between RF output ports of the pair of amplifying devices and an output port of the amplifier circuit wherein the first and second baluns are configured such that the amplifier circuit operates under open condition for signals at a second harmonic frequency even when the second harmonic frequency is within an operating frequency band of a fundamental frequency of the amplifier circuit. In one embodiment, the amplifier circuit includes a bypass circuit which selectively couples balun ports to ground such that in response to a first control signal, the amplifier circuit operates in an amplifying mode and in response to a second control signal, the amplifier circuit operates in a bypass mode.