Harmonic-Injection Doherty Power Amplifier: Benefits and Limitations

This paper presents an investigation into the effects of second harmonic ($2f_{0}$) power injection on the performance of a Doherty power amplifier (DPA). This investigation is conducted through the implementation of a single-stage 24 GHz harmonic-injection DPA (HI-DPA) manufactured on a 100 nm Gallium Nitride (GaN) technology. An on-chip injection power amplifier (IPA) operating at 48 GHz is used to generate the injected $2f_{0}$ power. On-wafer continuous wave measurements demonstrate that at 24 GHz, the HI-DPA achieves a power added efficiency (PAE) of 37% and 32.5% at a peak output power (POP) of 32.5dBm and 6 dB output power back-off (OPBO), respectively. When compared to a conventional DPA (CDPA) designed and manufactured under similar operating conditions, the HI-DPA exhibits an improved AM/PM characteristics with a 3.3% and 6% higher PAE at POP and OPBO at a cost of 1 dB small-signal gain penalty.