Harmonic-Injection Doherty Power Amplifiers with a High Small-Signal Gain

This paper presents a novel Doherty power amplifier (DPA) in which a second harmonic (2f0) current is injected into the drain of the auxiliary device. Hence, the name harmonic-injection Doherty power amplifier (HI-DPA). The performance parameters of the HI-DPA are analytically derived and show that the injection of a 2f0 current into the drain of the auxiliary device reduces the maximum current required from the auxiliary PA. Consequently, the portion of input power allocated to the auxiliary PA reduces, resulting in a significant improvement in small-signal gain (SSG) and power-added efficiency (PAE) compared to the conventional DPA. The analytical results are validated through the design and simulation of two GaN HEMTs single-stage HI-DPAs exhibiting a SSG of 9.5 and 13.6 dB at 3.6 GHz while maintaining a high PAE at peak and 6 dB back-off power.