Thermal noise measurements in GaAs MESFET´s

The absolute magnitude of the thermal drain current fluctuations and the associated effective thermal noise coefficient of 1-µm gate-length MESFET\´s have been measured under various bias conditions. At low drain-source voltages the magnitude of current fluctuations are in good agreement with the thermal noise theory which is based on the gradual channel approximation. However, under normal operating conditions ( V, ), we find for the thermal drain noise current A²/Hz with a noise coefficient in disagreement with the commonly used, theoretically predicted value P = 1.1. Our results are qualitatively consistent with a more comprehensive FET noise theory which properly takes into account high-field effects.