opamp design please help me ( emergency)

[e_ali_e]

Dear friends
my professor has asked this project fully diffrential CMOS opamp design, as a school project for one of my courses, and as i am not the student of I.C design p, i dont know, what should i do. and this is really vital for me, i will be really grateful if you help me, i am sure you know.
we are supposed to design in Hspice. with 0.35 technology
fully diffrential with common mode feedback.
Av>400
ωu ( unity gain)> 1Ghz
power=3.3 mw
RL=100k
P.M (phase margin) =70
VDD=3.3 ,25°c
vout ----- output swing ±0.8 ( vout>1.6)
and he has told us as much as you get the Av.ωu higher value the design is great.
i hope you can design this and help me. i am waiting for your happy responding. i should give the design after 5 days. it is really important to me.thank you again.

 

[susheelkoushik]

Hello,

Designing a fully differential circuit can be complex if u dont have the background for it. You can get the schematic of the circuit from any good analog IC design text. From there you'll get your unity gain frequency (GBW) equation and DC gain equation. GBW/A=bandwidth.

As a first step, you ll have to design the circuit for DC. You have a max power requirement of 3.3w and your supply is 3.3V, so that gives u the maximum current in your entire circuit (3.3m/3.3)=1mA. That shoud be enough.

So choose your design current to be some what less than 1mA. For example 400 uA. for your tail source. And you need a 0.8v peak-peak swing. You need to fix your output V0 a max of 3.3-vds(sat)_of_pmos-0.4. So choosing vdssat as 0.4v. you can pick V0=1.8.

As a first oder design, choose Vov (vgs-vth) of all PMOS as 0.4V and all Vov of all NMOS as 0.3V. From there you can calculate common mode input voltage Vin. With Vgs known, Id known, size your transistors to give you the current. Ensure everything is in saturation.

This is how you start. It involves other steps to achieve your final result.