AN EXTENDED FUKUI-LIKE FORMULA FOR THE MINIMUM-NOISE FIGURE OF MICROWAVE FETS

The article presents an extension of the well-known Fukui formula for the minimum noise figure of microwave FETs, based on a complete small- signal equivalent circuit including parasitic elements, the feedback c apacitance C(gd), and the output admittance (G(ds) and C(ds)). We show that the simplified circuit neglecting all of the above elements, on which most Fukui-like expressions are based, overestimates NF(min), ma inly because C(gd) is discarded; moreover, the linear approximation of NF(min)(f) from the complete circuit is more accurate than the quadra tic one, while parasitic inductances affect the terms of the series ex pansion of NF(min) in powers of f from the third order only. (C) 1994 John Wiley & Sons, Inc.