Exemplary impedance matching circuit for an amplifier device comprises a broadband impedance transformer configured to transform, over a fundamental frequency range, an impedance associated with an input port or an output port of the impedance matching circuit; and to transmit RF signals having a fundamental frequency within the fundamental frequency range. The impedance matching circuit also includes a phase shifter circuit configured to transmit, with substantially matched impedance, the RF signals having a fundamental frequency within the fundamental frequency range, and to phase-shift higher-order harmonics of the RF signals. The impedance matching circuit also includes a high-pass impedance transformer configured to match an impedance of the RF signals having a fundamental frequency within the fundamental frequency range; and to transmit, with low reflection, second-order harmonics of the RF signals. Exemplary embodiments also include amplifier circuits comprising an RF amplifier and embodiments of the impedance matching circuit.