A Wideband Modulator for an Envelope Tracking Amplifier of Cellular Base Stations

Akira MAEKI  

Publication
IEICE TRANSACTIONS on Communications   Vol.E96-B   No.10   pp.2703-2708
Publication Date: 2013/10/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E96.B.2703
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
Keyword: 
power amplifier,  envelope tracking,  envelope elimination and restoration,  cellular base station,  

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Summary: 
To develop an envelope-tracking (ET) amplifier for next-generation cellular base stations, we propose a wideband envelope modulator, consisting of a linear-mode class-B amplifier and a switch-mode class-D amplifier. The function of the modulator is to track the envelope signal and supply voltage to an RF amplifier. To meet the requirements of a large-current and high-voltage supply that can handle a wideband signal, an “Alexander current-feedback amplifier topology” is applied to the linear-mode class-B amplifier. The Alexander topology not only boosts the voltage but also enhances the current capacity of a commercial high-speed operational amplifier (op-amp) by means of a push-pull stage with current mirrors and a buffer amplifier at the output of the op-amp. With this topology, a linear-mode amplifier can provide several-ampere-level current to a 11-Ω load. A prototype of the wideband envelope modulator is shown to achieve the efficiency of 71% with a 20-MHz WiMAX envelope signal at output power of 72W.