A High Efficiency Doherty Amplifier with Digital Predistortion for WiMAX

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  • Author: Simon Wood, Ray Pengelly & Jim Crescenzi
The Doherty amplifier architecture is a well known technique offering the potential to improve transmitter efficiency especially for signal protocols that exhibit high peak-toaverage power ratios. Although the Doherty approach has significant efficiency advantages, it generally must be augmented with some form of correction or linearity enhancement in the full transmitter design. Wireless infrastructure applications have demanding linearity and spectral mask specifications. The latest WiMAX standards present a particular challenge with their combination of very high peak-to-average power ratios, 10 MHz or wider channel bandwidths and high linearity standards. This article demonstrates a 2.5-2.7 GHz Doherty amplifier that achieves, when augmented with digital predistortion, 8 watts of WiMAX average output power at greater than 47% efficiency, while satisfying demanding spectral mask specifications.