Load Insensitive Doherty PA Using Load Dependent Supply Voltages

Abstract

This paper presents optimal carrier and peaking drain voltages to preserve the output power capability and back-off level of Doherty power amplifiers (PAs) operating for non-optimal loads. These voltages are theoretically obtained from back-off and full power conditions. A performance comparison between simulations of a conventional Doherty and the proposed load insensitive version is presented, showing that the introduced theory can be very advantageous for operation under load varying scenarios. A 3.6 GHz load insensitive Doherty PA was designed, implemented and measured for loads distributed inside a 2.0 voltage standing wave ratio circle. These measurements validated the introduced theory, showing an almost constant maximum output power (42.9 – 43.2 dBm), and a back-off level varying between 5.0 dB and 6.2 dB. The 6-dB output power back-off efficiency varies between 42 % and 53 %, in which the highest degradation corresponds to loads with high imaginary parts.