A 4-mm-Square Miniaturized Doherty Power Amplifier Module for W-CDMA Mobile Terminals

Takayuki KATO

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E90-A    No.2    pp.310-316
Publication Date: 2007/02/01
Online ISSN: 1745-1337
DOI: 10.1093/ietfec/e90-a.2.310
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuit Techniques and Related Topics)
Doherty amplifier,  PA module,  W-CDMA,  mobile terminal,  GaAs MMIC,  

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Recently, the Doherty amplifier technique has been the focus of attention not only for base stations but also for mobile terminals because of its high power-added efficiency in the large back-off region. In this paper, we present a miniaturized Doherty power amplifier (PA) module for W-CDMA mobile terminals. The developed Doherty PA module consists of a 4-mm-square ceramic substrate (4.0 mm4.0 mm1.5 mm, alumina, dielectric constant = 8.8), a 1-mm-square GaAs MMIC (1.0 mm1.0 mm0.1 mm), and 0603-size SMD passive components. To miniaturize the module size, the optimal designed quarter-wavelength transmission lines, which are used for impedance conversion for carrier amplifier output and phase compensation for peak amplifier input, are embedded in the ceramic module substrate. Two GaAs HBTs for a carrier amplifier and a peak amplifier and base bias circuits for each amplifier are integrated onto a single-chip GaAs MMIC. Measurement results at 1950 MHz in a W-CDMA uplink signal indicate that 27 dBm of the maximum output power, 45% of the power-added efficiency (PAE), 11 dB of power gain, and 43% of PAE at 6 dB back-off, i.e. 24 dBm output power, are obtained with the developed Doherty PA. In other words, the PAE is improved from the theoretical PAE of a conventional class B amplifier, namely, from 23% to 43%. This is the smallest Doherty amplifier developed in the form of a module for mobile terminals.