Supply Modulation Behavior of a Doherty Power Amplifier

Dan Fishler,Zoya Popovic,Taylor Barton

doi:10.1109/jmw.2020.3039421

Dan Fishler, Zoya Popovic + Show 1 more

Open Access

https://doi.org/10.1109/jmw.2020.3039421

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Journal: IEEE Journal of Microwaves	Publication Date: Jan 1, 2021
Citations: 17	License type: CC BY 4.0

Affiliation: University of Colorado Boulder

Abstract

This paper presents a study of supply modulation in a Doherty power amplifier (DPA). To validate a simplified theoretical model, a 3.5 GHz conventional symmetrical DPA using a 6-W packaged GaN pHEMT is designed for supply modulation of the main and/or auxiliary amplifiers. The DPA is characterized in CW operation over a range of supply voltages, and shows up to 15 percentage point efficiency improvement at 12 dB output back-off when both main and auxiliary amplifiers are varied simultaneously. A comparison of three cases of supply variation is shown and potential benefits for improving back-off efficiency are discussed.

Highlights

Modern communications systems require high data rates confined within a limited spectrum, resulting in signals with peakto-average power ratios (PAPRs) exceeding 10 dB
supply modulation (SM) is typically applied to single-ended power amplifier (PA) as overviewed in e.g. [3], it has been successfully demonstrated with other efficiency enhancement techniques including Chireix outphasing [4], load-modulated balanced [5], [6] and Doherty PAs [7]–[11]
This work compares the benefits of supply modulation within a Doherty power amplifier (DPA) when the main and auxiliary PAs are modulated independently and together

Summary

Introduction

Modern communications systems require high data rates confined within a limited spectrum, resulting in signals with peakto-average power ratios (PAPRs) exceeding 10 dB. To maintain high efficiency in the power amplifier (PA) under these conditions, multiple efficiency enhancement techniques can be combined. The efficient output power range of the popular Doherty power amplifier (DPA) [1], [2] can be extended using supply modulation (SM). [3], it has been successfully demonstrated with other efficiency enhancement techniques including Chireix outphasing [4], load-modulated balanced [5], [6] and Doherty PAs [7]–[11]. Modulating the MPA [8], [9] was shown to increase efficiency in back-off by 15 percentage points [8], while modulating the APA supply was shown to increase efficiency in the highpower regime [10]. Modulating both MPA and APA supplies together increases the back-off efficiency range [11]

Methods

Conclusion