Induced gate noise in MOS FET's

Abstract

Input admittance, drain noise and induced gate noise measurements are reported on several MOS FET's of large geometry. A few units show excess gate noise as found earlier by Halladay and van der Ziel. Other units show the gate noise expected from the thermal noise of the channel. No evidence was found of induced flicker gate noise even in noisy units that showed flicker drain noise up to 30 MHz. Rao and van der Ziel have shown theoretically that Christensson, et al's flicker noise models should give clearly observable flicker gate noise if a noticeable amount of flicker drain noise is present. Since none was observed, this indicates that these models may not be correct. Experiments seem to indicate that the h.f. input conductance g 11 varies as ƒ 3 2 in MOS-units with gate overlap whereas g 11 varies as ƒ 2 in MOS-units with no gate overlap. There is at present no satisfactory explanation for this difference; an ƒ 2 frequency dependence is expected theoretically.