The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> cmos fully differential amp voltage scaling
https://designers-guide.org/forum/YaBB.pl?num=1135615367

Message started by steven on Dec 26^th, 2005, 8:42am

Title: cmos fully differential amp voltage scaling
Post by steven on Dec 26^th, 2005, 8:42am

Hi,

I obtained a cmos fully differential folded cascode circuit. The circuit was designed on 2um process. Now the same will be used on 0.18um for a prototype. I wonder if there is a better way to scale the bias voltages in the circuit (Vdd and Vss are still the same as the original circuit).

Thanks

Title: Re: cmos fully differential amp voltage scaling
Post by irfan on Jan 8^th, 2006, 3:14pm

In my opinion it is a new design. Sure the architecture is the same, but the 0.18-um process is about at least six or seven generations ahead of the 2-um process. You will have to watch out for the following:

(1) Break down voltages for the 0.18-um process as the supplies from the 2-um design haven't changed
(2) Sure, Vth & Lmin are small now, but watch out for the voltage dependent Rds & gm as both Vth & L_effective have voltage dependency now.
(3) Lower Vth, will also lower your maximum output swing
(4) More leakage current in stand-by mode

That's all I can think of now. The last time I desgined a folded cascode in 0.18-um was back in 2001. If you need more help, I can dig up my old notes. :)

Title: Re: cmos fully differential amp voltage scaling
Post by steven on Jan 8^th, 2006, 7:33pm

Hello Irfan,

What you pointed out is correct. Maybe your notes have something not covered. Anyway, the notes should be helpful.

Regards,
Steven

Title: Re: cmos fully differential amp voltage scaling
Post by ywguo on Jan 10^th, 2006, 3:40am

Steven,

I guess that the original design (2um) is operater at 5V supply that may destroy a 0.18um circuit eventually.

yawei

Title: Re: cmos fully differential amp voltage scaling
Post by steven on Jan 10^th, 2006, 10:29am

Hello Yawei,

This is a good point. So some level shifting may come as an option? I would see how Irfan's design approach.

Steven

Title: Re: cmos fully differential amp voltage scaling
Post by zhonghan on Jan 15^th, 2006, 8:55pm

it is easier to adjust biases for the circiuts than to reduce the power voltage.

I am a new comer of the community ,very glad to discuss problems with you.