Response Time of VSWR Protection for GaN HEMT based Power Amplifiers
Proc. 46th European Microwave Conf. (EuMC 2016), London, UK, Oct. 4-6, pp. 401-404 (2016).
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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
BST, ceramics, GaN, HEMT, power amplifier, varactors, VSWR.