Digital Doherty Transmitter with Envelope ΔΣ Modulated Class-D GaN Power Amplifier for 800 MHz band

K. Motoi1, A. Wentzel2 , M. Tanio1, S. Hori1, M. Hayakawa1, W. Heinrich2, K. Kunihiro1

Published in:

IEEE MTT-S Int. Microw. Symp. Dig., Tampa Bay, USA, Jun 1-6, TU4F-1 (2014).

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Abstract:

This paper presents a novel transmitter (Tx) architecture combining voltage-mode class-D power amplifiers (PAs) with an efficient 1-bit envelope delta-sigma modulation scheme for the 800 MHz band. By digitally processing the input 1-bit codes, the proposed Tx operates as a digital Doherty Tx. The proposed Tx architecture is realized with a GaN H-bridge class-D PA module and CMOS modulator ICs and delivers a CW power of 35.9 dBm at 860 MHz with a final-stage drain efficiency of 75.6% at the saturation point. The drain efficiency at 6-dB BO is still 73.4% which corresponds to an improvement of 23.9 points compared to balanced operation. Using a CDMA signal of 1-MHz bandwidth and 6.5-dB peak-to-average power ratio, the digital Doherty Tx achieves an average output power of 28.6 dBm with a drain efficiency of 56.5%.

1 NEC Corporation, Kawasaki, Kanagawa, 211-8666, Japan
2 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany

Index Terms:

Class-D, GaN, MMIC, H-Bridge, CMOS, delta-sigma-modulation, Doherty power amplifier.