I'm synthesizing a microwave PA @ 2.4 GHz using sub 200nm CMOS technology. I've choosen cascode topology. The upper transistor configs are: wtot = 400u/multiplicity, number of fingers = 3 and multiplicity = 9.
My doubt: Is there any constraint when using a large multiplicity number as I've used? How the large multiplicity number will affect my layout?
More the multiplier, more the parasitic due to layout (more routing connecting different multiplier). But if you are using RF transistor model for the design, I assume the parasitic are well modeled and you will see very little change from schematic to layout results. However, there is a limit on the maximum number of fingers that can be used. Multiplier of 9 is not too large.