Fully-Integrated Two-Stage GaN MMIC Doherty Power Amplifier for LTE Small Cells

A novel two-stage Doherty power amplifier (PA) was designed and fully integrated on a 0.25-μm GaN on SiC monolithic microwave integrated circuit die with a dimension of 3.3 × 2.6 mm ² to build small-cell base stations. An asymmetric Doherty configuration was adopted for the power stage with the reversed uneven input power splitting network for better performance. To improve linearity, the third-order intermodulation distortion (IMD3) was minimized by cancelling IMD3s between the carrier and peaking amplifiers. The two-section quarterwave transformer was used for more uniform in-band frequency responses. The fabricated PA showed a power-added efficiency of 46.8% and a power gain of 30.9 dB at an average power of 35.1 dBm for a 2.655-GHz long-term evolution signal with a 7.1-dB peak-to-average power ratio. The adjacent channel leakage ratio was -40.2 dBc without any linearization, and it was lowered to -49.3 dBc by a digital pre-distortion linearization.