A Doherty Power Amplifier With a GaN MMIC for Femtocell Base Stations

A Doherty Power Amplifier (PA) with the proposed GaN MMIC for femtocell base stations is presented. The MMIC was fabricated using a 0.25 μm TriQuint GaN process. An on-chip quadrature coupler based on a lumped magnetic coupler with capacitors was used to reduce the chip size. The MMIC with an area of 2.5 × 2.7 mm² includes an input matching circuit, a driver transistor, carrier and peak transistors at power stage, and an inter-stage matching network with the quadrature coupler. The Doherty PA with MMIC shows 56.2% power added efficiency (PAE) with a gain of 19.7 dB when the output power is 41.2 dBm for a 2.14 GHz CW signal. For a down link WCDMA signal, the PAE of 39.6% is achieved at an output power of 35.3 dBm. The Doherty PA with the MMIC presented here has a small effective module area of 7 × 15 mm², which can be readily reduced further.