RFICDUDE wrote on Feb 16th, 2014, 5:04am:Hi Baab,
Looks like you did not recalculate or remeasure Cgs after you scaled the width from 24um to 773um to raise gm from 14mS to 442mS. Cgs is proportional to width, so Cgs will increase by a factor of 32.
Thanks. However, let's me explain it a bit more.
As in the picture, first I calculated optimum Q for minimum NF.
From Q computed, the total Cgs is determined with the formula:
Cgs = 1/(Omega* Q* 50Ohms)
(Cgs here is the capacitance with minimum NF, after Cgs is calculated I need to resize the width of transistors to get the Cgs value)
And from that Cgs I can figure out the total width of transistors with the formula:
W (final W) = Cgs/(2/3 * Cox* L)