Abstract: In this paper, an X -band pseudomorphic HEMT power amplifier (PA) is reported with two kinds of hysteresis phenomena; the first occurs in the dc-IV measurement, and the second is observed in the power measurement. The unusual phenomena can be attributed to the gate current resulting from the impact ionization coupling with the gate bias resistor, which is usually observed in the design of RF circuits to provide the gate bias. After the gate current is considered, two methods are proposed to analyze the hysteresis with the same conclusion. The cause of the encountered hysteresis is for the first time identified, and criteria for the selection of the gate bias resistor in order to avoid the hysteresis are proposed. Finally, a PA complying with these criteria is presented with good performances and without hysteresis.

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