Compact Load Network for GaN-HEMT Doherty Power Amplifier IC Using Left-Handed and Right-Handed Transmission Lines

This letter presents a compact load network for Doherty power amplifier (DPA) integrated circuits (ICs) using π-type left-handed (LH) and right-handed (RH) transmission lines (TLs) based on lumped components. The quarterwave impedance transformers based on the LH TLs and a compensation method for the internal shunt capacitance using a shunt inductor were adopted for the impedance matching networks. The π-type LH and RH TLs for the matching networks and a combining network can be further simplified by merging adjacent shunt components. In order to verify the proposed load network, a 2.6-GHz DPA IC was designed and fabricated using a 0.4-μm gallium nitride high-electron-mobility transistor process for small-cell base stations. The overall size of the chip is 1.7 × 1.8 mm² and the chip was mounted on a quad flat no-leads package. For a long term evolution signal with a signal bandwidth of 10 MHz and a peak-to-average power ratio of 6.5 dB, a high drain efficiency of 52.2% was obtained at an average output power of 34.0 dBm.