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J. Electromagn. Eng. Sci > Volume 11(1); 2011 > Article
Journal of the Korean Institute of Electromagnetic and Science 2011;11(1):16-26.
DOI: https://doi.org/10.5515/JKIEES.2011.11.1.016   
GaN HEMT Based High Power and High Efficiency Doherty Amplifiers with Digital Pre-Distortion Correction for WiBro Applications
Jun-Chul Park1, Dong-Su Kim2, Chan-Sei Yoo2, Woo-Sung Lee2, Jong-Gwan Yook1, Sang-Hyun Chun3, Jong-Heon Kim3, Cheol-Koo Hahn2
1School of Electrical & Electronic Engineering, Yonsei University
2Korea Electronics Technology Institute
3Department of Radio Science and Engineering, Kwangwoon University
Abstract
This paper presents high power and high efficiency Doherty amplifiers for 2.345 GHz wireless broadband (WiBro) applications that use a Nitronex 125-W ($P_{3dB}$) GaN high electron mobility transistor (HEMT). Two- and three-way Doherty amplifiers and a saturated Doherty amplifier using Class-F circuitry are implemented. The measured result for a center frequency of 2.345 GHz shows that the two-way Doherty amplifier attains a high $P_{3dB}$ of 51.5 dBm, a gain of 12.5 dB, and a power-added efficiency (PAE) improvement of about 16 % compared to a single class AB amplifier at 6-dB back-off power region from $P_{3dB}$. For a WiBro OFDMA signal, the Doherty amplifier provides an adjacent channel leakage ratio (ACLR) at 4.77 MHz offset that is -33 dBc at an output power of 42 dBm, which is a 9.5 dB back-off power region from $P_{3dB}$. By employing a digital pre-distortion (DPD) technique, the ACLR of the Doherty amplifier is improved from -33 dBc to -48 dBc. The measured result for the same frequency shows that the three-way Doherty amplifier, which has a $P_{3dB}$ of 53.16 dBm and a gain of 10.3 dB, and the saturated Doherty amplifier, which has a $P_{3dB}$ of 51.1 dBm and a gain of 10.3 dB, provide a PAE improvement of 11 % at the 9-dB back-off power region and 7.5 % at the 6-dB back-off region, respectively, compared to the two-way Doherty amplifier.
Key words: Class-F, Digital Pre-Distortion (DPD), Doherty Amplifier, Gallium Nitride (GaN), WiBro
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