3. Doherty Power Amplifier

The chapter delves into the design and integration of Doherty Power Amplifiers, a technique that combines Class-A and Class-C amplifiers to improve efficiency and output power. It begins by explaining the basic principles of Doherty amplifiers and their load modulation technique. The design process is broken down into three main steps: the design of the Class-A amplifier, the Class-C amplifier, and the combining of the two circuits using quarter wavelength transmission lines. The chapter also discusses transistor sizing and the simulation process to determine the maximum frequency of operation. The integration of the Doherty amplifier is detailed, including the current representation of the main and auxiliary PAs and the design of the matching networks. The chapter concludes with simulation and measurement results, showcasing the performance of the Doherty amplifier under different biasing conditions.