Re: current source
Fisrt of all, you are using biggger technology (1.6um)...it's voltage trashold is bigger(about 1V). To use a CMOS current source is very difficult as at least 2 transistor is needed in CMOS tech(NMOS & PMOS)! Unless, you can used only one transistor as for example 1 NMOS and will be functioned as active resistor(as depcited below).
You can use these equation to define your W&L
W/L = 2Id/[Kn(Vgs1 - Vt)*(Vgs1 - Vt1)]
= 2(50n)/[Kn(2 - Vt)*(2 - Vt1)]
* Add your Kn and Vt form your 1.6um parameter.
Try to simulate, I think that circuit sholud works properly!