Development of a wideband MMIC Doherty Power Amplifier for 5G applications in the FR1 frequency bands

Power amplifiers, being one of the last stages of the transmitter branch of a wireless communication system, are one of the key components that heavily affects the overall performance. Nowadays communication systems are required to be compact and affordable. For their cooling system to be simple and small the power amplifiers should be efficient. The evolution of wireless communications moves toward higher data rates which need wider frequency bands and higher complexity modulation schemes. These solutions lead to a high peak-to-average power ratio, therefore the ability of a power amplifier to maintain its performance in terms of efficiency and linearity for lower power levels has become crucial. In this context the Doherty amplifier has become one of the most popular solutions for back-off efficiency enhancement. Having two amplifiers combined through a load-modulation network it can maintain high efficiency across a large power range. The proposed thesis presents the design of an MMIC Doherty Power Amplifier for 5G applications in the FR1 frequency bands (3.3-5) GHz. The amplifier achieves 37 dBm of saturated output power and 20 dB of small-signal gain over a 41% operating bandwidth. The minimum efficiency over a 6 dB back-off range is 25% while efficiency at break is equal or lager than the saturation value. This result shows the effective efficiency enhancement behavior of the circuit and the improvement with respect to a Class B power amplifier that would present about half of the efficiency at 6 dB back-off. To the best of my knowledge the designed Doherty amplifier achieves the widest bandwidth among the Monolithic integrated circuit GaN DPAs reported in the literature with a two-stage configuration and at least 37 dBm of saturated output power. The design has been carried out on a 150 nm GaN HEMT process exploiting the material superior power density to achieve more than 5 W delivered output power in a 3.7mm x 3.3mm chip area. PathWave Advanced Design System has been used for circuit simulation. The design implements a two-section peaking combiner specific for wideband performance. The present thesis work is part of a commercial project pursued by the faculty mentor and her research group on a wideband high efficiency Doherty power amplifier for FR1 bands and it constitutes the first step toward the circuit realization. The design is being manufactured by WIN Semiconductors Corp and measurements to assess simulated results will follow. Future developments of the research project foresee to address in a comprehensive manner the topic of load insensitivity and to investigate linearity enhancement techniques to be included in subsequent power amplifier design.