A Multimode GaN Doherty Power Amplifier MMIC With N-Scalable Amplifiers for Selective Back-Off Power Level

This article presents a multimode Doherty power amplifier (M-DPA) monolithic microwave integrated circuit (MMIC). The M-DPA comprises of a load network (LN) based on a combination of current- and voltage-combining methods. By arranging the turn-on transitions of four parallel amplifiers based on the input power level, two carrier and two peaking amplifiers (2C2P) mode for 6-dB output power back-off (OBO) or one carrier and three peaking amplifiers (1C3P) mode for 12-dB OBO can be configured. The performances between efficiency and gain can be balanced according to the selected mode. The M-DPA concept was theoretically expanded to a generalized structure based on $N$ (or = $2^{m}$ ) scalable amplifiers in parallel that were simply modeled as current sources. This generalized M-DPA supports $N-1$ different operation modes with $m$ different OBO levels. For verification, the M-DPA MMIC was implemented using a 0.25- $\mu \text{m}$ gallium nitride (GAN)-HEMT process for 5G new radio (NR) applications (3.3-3.6-GHz band). Using a 5G NR downlink signal with a signal bandwidth of 100 MHz and a peak-to-average power ratio (PAPR) of 7.86 dB, at a frequency of 3.55 GHz, the drain efficiencies (DEs) of 37.7 and 33.8% and power gains of 8.3 and 6.4 dB were obtained for the 2C2P mode with an average output power of 37.0 dBm and for the 1C3P mode with an average output power of 31.0 dBm, respectively.