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Predicting the performance of a power amplifier using large-signal circuit simulations of an AlGaN/GaN HFET model
Author(s): Griff L. Bilbro; Danqiong Hou; Hong Yin; Robert J. Trew
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Paper Abstract

We have quantitatively modeled the conduction current and charge storage of an HFET in terms its physical dimensions and material properties. For DC or small-signal RF operation, no adjustable parameters are necessary to predict the terminal characteristics of the device. Linear performance measures such as small-signal gain and input admittance can be predicted directly from the geometric structure and material properties assumed for the device design. We have validated our model at low-frequency against experimental I-V measurements and against two-dimensional device simulations. We discuss our recent extension of our model to include a larger class of electron velocity-field curves. We also discuss the recent reformulation of our model to facilitate its implementation in commercial large-signal high-frequency circuit simulators. Large signal RF operation is more complex. First, the highest CW microwave power is fundamentally bounded by a brief, reversible channel breakdown in each RF cycle. Second, the highest experimental measurements of efficiency, power, or linearity always require harmonic load pull and possibly also harmonic source pull. Presently, our model accounts for these facts with an adjustable breakdown voltage and with adjustable load impedances and source impedances for the fundamental frequency and its harmonics. This has allowed us to validate our model for large signal RF conditions by simultaneously fitting experimental measurements of output power, gain, and power added efficiency of real devices. We show that the resulting model can be used to compare alternative device designs in terms of their large signal performance, such as their output power at 1dB gain compression or their third order intercept points. In addition, the model provides insight into new device physics features enabled by the unprecedented current and voltage levels of AlGaN/GaN HFETs, including non-ohmic resistance in the source access regions and partial depletion of the 2DEG in the drain access region.

Paper Details

Date Published: 12 February 2009
PDF: 14 pages
Proc. SPIE 7216, Gallium Nitride Materials and Devices IV, 721603 (12 February 2009); doi: 10.1117/12.803348
Show Author Affiliations
Griff L. Bilbro, North Carolina State Univ. (United States)
Danqiong Hou, North Carolina State Univ. (United States)
Hong Yin, Skyworks Solutions, Inc. (United States)
Robert J. Trew, North Carolina State Univ. (United States)

Published in SPIE Proceedings Vol. 7216:
Gallium Nitride Materials and Devices IV
Hadis Morkoç; Cole W. Litton; Jen-Inn Chyi; Yasushi Nanishi; Joachim Piprek; Euijoon Yoon, Editor(s)

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