Analysis and Design of a High-Efficiency Multistage Doherty Power Amplifier for WCDMA

Abstract

A comprehensive analysis of multistage Doherty amplifier, which can be used to achieve higher efficiency at greater back-off compared to the classical Doherty amplifier, is presented. A novel set of design equations for a generalized N-stage Doherty amplifier is introduced. For the first time, this technique is applied to the design of a WCDMA power amplifier (PA). The designed PA meets WCDMA requirements, and exhibits a power-added efficiency (PAE) of 34.5% at 6 dB back-off and 16.9% at 12 dB back-off. These PAEs are 2 times and 4 times better, respectively, than that of a single stage linear PA at the same back-off levels. The PA is capable of delivering up to 28.6 dBm of output power, and has a maximum adjacent channel power leakage ratio of -38 dBc and -51 dBc at 5 and 10 MHz offset, respectively. To the best of the authors' knowledge, these represent the best reported results of a Doherty amplifier for WCDMA application in the 1.95 GHz band, to date.