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A comprehensive comparison between GaN MMIC Doherty and combined class-AB power amplifiers for microwave radio links

Published online by Cambridge University Press:  11 February 2016

Rocco Giofrè ,
Paolo Colantonio ,
Franco Giannini ,
Chiara Ramella ,
Vittorio Camarchia ,
Mustazar Iqbal ,
Marco Pirola  and
Roberto Quaglia
Rocco Giofrè*
Affiliation:
Electronic Engineering Department, University of Roma Tor Vergata, 00133 Roma, Italy. Phone: +39 06 7259 7346
Paolo Colantonio
Affiliation:
Electronic Engineering Department, University of Roma Tor Vergata, 00133 Roma, Italy. Phone: +39 06 7259 7346
Franco Giannini
Affiliation:
Electronic Engineering Department, University of Roma Tor Vergata, 00133 Roma, Italy. Phone: +39 06 7259 7346
Chiara Ramella
Affiliation:
Electronic Engineering Department, University of Roma Tor Vergata, 00133 Roma, Italy. Phone: +39 06 7259 7346
Vittorio Camarchia
Affiliation:
Electronics and Telecommunications Department, Politecnico di Torino, 10129 Torino, Italy
Mustazar Iqbal
Affiliation:
Electronics and Telecommunications Department, Politecnico di Torino, 10129 Torino, Italy
Marco Pirola
Affiliation:
Electronics and Telecommunications Department, Politecnico di Torino, 10129 Torino, Italy
Roberto Quaglia
Affiliation:
Electronics and Telecommunications Department, Politecnico di Torino, 10129 Torino, Italy School of Engineering, Cardiff University, Cardiff, CF24 3AA, UK
*
Corresponding author:R. Giofrè Email: giofr@ing.uniroma2.it
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Abstract

A combined class-AB and a Doherty power amplifier conceived for microwave backhaul in the 7 GHz frequency band are here presented and compared. They are fabricated in the same GaN monolithic process and have identical total active device periphery. For the given application, the linearity-efficiency trade-off for the two architectures is discussed. The two modules have been thoroughly characterized in linear and non-linear continuous wave conditions. Then, to evaluate linearity under the actual operative conditions, a system level characterization has been carried out, applying a modulated input signal and comparing the spectral responses of the two amplifiers with and without digital predistortion. A saturated output power of 40 dBm has been achieved by both circuits. At 6 dB of output back-off, the Doherty amplifier shows an efficiency of 33%, 10 points higher than that of the class-AB module. On the other hand, system level measurements show that, adopting the same predistorter complexity to comply with the reference standard emission masks, the Doherty amplifier needs at least 1 dB of extra back-off. This negatively affects its efficiency, therefore reducing the advantages it can claim with respect to the class-AB amplifier in continuous wave condition.

Keywords

Circuit design and applicationsPower amplifiers and linearizers
Type
Research Papers
Information
International Journal of Microwave and Wireless Technologies , Volume 8 , Special Issue 4-5: EuMW 2015 Special Issue , June 2016 , pp. 673 - 681
Copyright
Copyright © Cambridge University Press and the European Microwave Association 2016 

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