Hi estradasphere, How about if i only need a very narrowband (2.11G-2.17Ghz, BW = 60Mhz)?
hi,
if you want to make an "on-chip" narrow-band matching, then it is more critical, because you have to realize your input match exactly at 2.1 GHz (if you intend to make an off-chip matching with a package, then this is no more critical). i would run a simple s-parameter monte-carlo simulation (takes maybe 20 minutes) and see the variation of the input match. the lna should be as simple as possible and i would avoid to use too many elements in my circuit.
to your question; in my opinion, keeping the W/L ratio constant, the circuit with the smaller L would give the smallest NF, because, you get the same gain with less transistors, which means less noise and less parasitics. please correct me, if i'm wrong.