Response Time of VSWR Protection for GaN HEMT based Power Amplifiers

S. Preis1, J. Ferretti1, N. Wolff1, A. Wiens2, R. Jakoby2, W. Heinrich1, O. Bengtsson1

Published in:

Proc. 46th European Microwave Conf. (EuMC 2016), London, UK, Oct. 4-6, pp. 401-404 (2016).

Copyright © 2016 EuMA. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the EuMA.

Abstract:

Protection against high voltage-standing-wave-ratios (VSWR) is of great importance in many power amplifier applications. Despite excellent thermal and voltage breakdown properties even gallium nitride devices may need such measures. This work focuses on the timing aspect when using barium-strontium- titanate (BST) varactors to limit power dissipation and gate current. A power amplifier was designed and fabricated, implementing a varactor and a GaN-based voltage switch as varactor modulator for VSWR protection. The response time until the protection is effective was measured by switching the voltages at varactor, gate and drain of the transistor, respectively. It was found that it takes a minimum of 50 µs for the power amplifier to reach a safe condition. Pure gate pinch-off or drain voltage reduction solutions were slower and bias-network dependent. For a thick-film BST MIM varactor, optimized for speed and power, a switching time of 160 ns was achieved.

1 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchoff-Strasse 4, 12489 Berlin, Germany
2 Institut fuer Mikrowellentechnik und Photonik, Technische Universitaet Darmstadt, Merckstrasse 25, 64283 Darmstadt, Germany

Keywords:

BST, ceramics, GaN, HEMT, power amplifier, varactors, VSWR.