Design Methodology Using Single Resonate Block for Harmonic Impedance Matching in GaN MMIC Doherty Amplifier

This letter presents a novel harmonic impedance matching technique by using a parallel LC resonate block after the combining point to design a fully integrated high-efficiency Doherty power amplifier (DPA). The second harmonic impedances of both carrier and peaking amplifiers can be matched to the optimal area with only one harmonic tuner easily. The insertion loss and size of the output matching network (OMN) can be reduced. For verification, a 4.6-5.2-GHz monolithic microwave integrated circuit DPA was designed and fabricated using a 0.25-mu m gallium nitride (GaN)-HEMT process. Experimental results show that a saturated power of 41.8-42.1 dBm, a saturated drain efficiency (DE) of 63.8%-68.4%, and a 6-dB back-off DE of 53.3%-57.4% are achieved from 4.6 to 5.2 GHz. For a 160-MHz modulated signal, a high DE of 54% with good linearity after linearization is obtained at an average output power of 35.6 dBm.