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

M. Akmal, V. Carrubba, J. Lees, S. Ben Smida, J. Benedikt, K. Morris, M. Beach, J. McGeehan, P. J. Tasker

Research output: Chapter in Book/Report/Conference proceedingConference contribution

13 Citations (SciVal)


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 IM 3 and IM 5 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 IM 3 and IM 5 baseband impedances disperse, becoming reactive and moving away from the real axis.
Original languageEnglish
Title of host publication2011 IEEE MTT-S International Microwave Symposium
ISBN (Electronic)9781612847573
ISBN (Print)9781612847542
Publication statusPublished - 4 Aug 2011


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