Noise characteristics of gallium arsenide field-effect transistors

Small signal and noise characteristics for GaAs field-effect transistors are derived with the saturated drift velocity of the carriers underneath the gate taken into account. The noise contributed by the saturated carriers is nonnegligible and in most cases, exceeds the noise generated by the unsaturated region. Parasitic elements contribute importantly by preventing the full cancellation of the correlated noise of the intrinsic transistor and by adding their own Johnson noise. The theory predicts the experimentally observed trend of noise figure dependence on drain current and on source-to-drain voltage. The present theory doesnot take into account the effects of a possible short negative resistance region underneath the gate.