The purpose of this application note is to give some general basic guidelines to bias high-power GaAs FET devices safely. However these guidelines are not a complete insurance against oscillations since each device is a unique case and its stability has to be analyzed by using standard methods if needed.
While considerable effort is spent by the semiconductor companies on characterizing high-power GaAs FET devices in RF and how to match them, little effort is spent for the bias techniques. Experience shows that a lot of amplifier designers spend significant time trying to solve stability problems. These problems are due to the fact that high-power devices have very large gate periphery and consequently large transconductance. Several issues specific to high-power devices have to be addressed for the design of the bias circuits and for the turn-on and –off sequences of these devices.
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