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Linearity enhancement of GaN HEMTs under complex modulated excitation by optimizing the baseband impedance environment

Akmal, Muhammad, Carrubba, Vincenzo, Lees, Jonathan, Bensmida, S., Benedikt, Johannes, Morris, K., Beach, M., McGeehan, J. and Tasker, Paul J. 2011. Linearity enhancement of GaN HEMTs under complex modulated excitation by optimizing the baseband impedance environment. Presented at: 2011 IEEE/MTT-S International Microwave Symposium, Baltimore, MD, USA, 5-10 June 2011. Published in: Seigel, Peter, Remley, Kate, Tzuang, C. and Ponchak, George eds. 2011 IEEE/MTT-S International Microwave Symposium - MTT 2011. New York: IEEE, pp. 1747-1750. 10.1109/MWSYM.2011.5972833

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This paper demonstrates how the linearity performance of a 10 W GaN HEMT can be dramatically improved by actively engineering the baseband impedance environment around the device. An important refinement to existing active load-pull measurement capability is proposed that allows the precise and independent control of all significant baseband and RF components that result from the amplification of a complex 9-carrier multi-sine modulation. The synthesis of constant, modulation frequency independent negative baseband impedances, resulting in specific baseband voltage waveforms has delivered a 24 dB improvement in ACPR compared to the classical baseband short case, even when the device is operating with RF components terminated into a non-optimal 50Ω RF environment. This linearization concept is further investigated through the broadband emulation of a class-J impedance environment around a single device. Using this enhanced system and a two-tone modulated excitation, optimum baseband loads are identified that result in a 18.5 dB and 24 dB improvement in IM3 and IM5 inter-modulation products respectively, again relative to the case of a traditional IF short circuit. The significance of this last observation is that unlike the 50Ω case, the optimum class-J IM3 and IM5 baseband impedances disperse, becoming reactive and moving away from the real axis.

Item Type: Conference or Workshop Item (Paper)
Status: Published
Schools: Engineering
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
Uncontrolled Keywords: Active load-pull; baseband; harmonics; memory effects; power device
Additional Information: Proceedings of a meeting held 5-10 June 2011, Baltimore, Maryland, USA
Publisher: IEEE
ISBN: 9781612847542
Last Modified: 04 Feb 2018 02:53

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