Challenges in Power Amplifier Design in RFIC/MMIC Technology
In order to handle the challenges in the rapid evolution of wireless communication standards and facilitate the integration of complete transceiver modules, broadband and multiband CMOS Power Amplifier (PA) has gained attention. Although CMOS has been best choice due to its high level of integration, PA design using this technology poses a bottleneck in integration with the presence of inductor. An RFIC PA with an inductorless architecture can help in utilizing the advantage of high level of integration and low cost of the CMOS technology. Due to low breakdown and high knee voltage of CMOS technology, the drain to source voltage swing is limited and hence the output power and efficiency are less for CMOS PAs. Therefore, realizing high-power amplifier with CMOS technology is a challenge. The popular technique to overcome this bottleneck is the stacked topology. A number of transistors can be stacked with the first transistor as common source (CS) and the cascoded transistors in the common gate (CG) configuration, thereby increasing the voltage swing. The CS and CG transistors in stacked topology are connected such that the voltage swings of the transistor would be added in phase at the output while maintaining the drain current constant. As the number of transistors increases in stacked topology, the optimum load impedance increases compared to single transistor which helps in designing the matching network with low impedance transformation and thereby high bandwidth. Alternatively, the PA can also be realized using Gallium Nitride (GaN) Monolithic Microwave Integrated Circuits (MMIC). GaN MMIC based technology has several advantages in terms of high bandwidth, high power density, high breakdown electric field and high electron saturation carrier velocity in comparison with other competing technologies. Hence PAs with high power can be realized with relatively very less form factor compared to its RFIC counterparts. This talk discusses various design strategies for implementing power amplifiers using RFIC and GaN MMIC technologies.