Asymmetric Broadband Doherty Power Amplifier Using GaN MMIC for Femto-Cell Base-Station

A power amplifier (PA) for a femto-cell base station should be highly efficient and small. The efficiency for amplification of a high peak-to-average power ratio (PAPR) signal is improved by designing an asymmetric Doherty power amplifier (DPA). From the simulation result for a long-term evolution (LTE) signal with 7.2-dB PAPR, the DPA delivers the highest efficiency with 1:1.4 cell size ratio for the carrier and peaking PAs. A small size is achieved by designing the DPA using a GaN monolithic microwave integrated circuit process. For broadband operation, we employ a new circuit topology to alleviate the bandwidth limiting factors of the DPA such as a quarter-wavelength transformer, phase compensation network, and offset line. With the design concept, an asymmetric broadband DPA is implemented using a TriQuint 3MI 0.25-μm GaN-HEMT MMIC process. Across 2.1-2.7 GHz, the implemented PA deliver a drain efficiency of over 49%, a gain of over 12.6 dB, and adjacent channel leakage ratio of below -45 dBc at an average power of over 33.1 dBm for the LTE signal. This fully integrated circuit has a chip-size of 2.65 mm×1.9 mm.