Mixed analog/digital design of wireless Doherty power amplifiers and transmitters

This paper exposes a number of analog and digital techniques for performance enhancement of Doherty power amplifiers (PAs). After briefly introducing the operation principle of the Doherty PA, the gain and phase impairments between the main and auxiliary amplifiers as well as the problem of power drive waste into the auxiliary branch at the low power mode are analyzed. Due to the dynamic nature of these problems, analog-based approaches cannot completely compensate for them. The digital Doherty PA architecture is then pointed out as the most suitable topology that enables an optimal operation of the Doherty PA. This architecture allows for the implementation of advanced digital signal processing algorithms, such as adaptive input power distribution and dynamic phase alignment that are experimentally proven to bring substantial performance enhancement.