cascode on paper/cadence

[Matteo]

hi all!
I would like to design a cascode configuration and my target are:
- gain 20
- Vout DC = 1.8 volt

I calculated some values on paper and I simulated my circuit but the
results are completely different!
my circuit is here: http://www.thebags.it/listing/uni/cascode.png

if I want Vout = 1.8V
Rd*Id = 1.5V; Rd = 600ohm so Id = 2.5mA

if I want Av = gm2 * (Rd//r02) = 20 I have to choose Vov = 0.10V and
so Vgs = 668mV

if I want Id = 2.5mA and Vov = 0.10 W has to be W=1080u

....I set these values in cadence but the risult is completely
different! Can you try to explain me why?
any help is appreciated

thank you (and sorry for my english..)