A High Efficiency Doherty Power Amplifier MMIC With Active Second Harmonic Injection Technique

In this brief, a novel design methodology for Doherty power amplifier (DPA) MMIC is proposed to improve the efficiency of the DPAs. The design equations of a compact harmonic-controlled bias network (CHCBN) are derived, which can achieve inverse class-F amplifier load conditions with adjustable fundamental frequency impedance, this approach effectively improves the saturated and back-off efficiency of the DPA. An active second harmonic injection network (HIN) is proposed which utilizes the second harmonic components generated by the carrier and peaking devices for mutual injection to achieve the amplitude modulation of the DPA drain waveform in the saturated state, further improving the saturated efficiency of the DPA. To validate the methodology, a C-band high efficiency DPA MMIC is designed and fabricated in a 0.25 μm GaN-HEMT process. The measurement results show that the fabricated DPA exhibits the saturated output power (Psat) of 39.6 dBm–40.6 dBm, with a saturated drain efficiency (DE) of 53.9%–61.5%, and a 6-dB back-off DE of 51.4%–56.0% over the 4.8-5.4 GHz frequency band. The proposed DPA demonstrates the highest 6-dB back-off efficiency among the published broadband GaN MMIC DPAs operating in similar frequency band.