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Design >> Analog Design >> How to find the process parameters
https://designers-guide.org/forum/YaBB.pl?num=1324623574

Message started by sri.sagar on Dec 22^nd, 2011, 10:59pm

Title: How to find the process parameters
Post by sri.sagar on Dec 22^nd, 2011, 10:59pm

Hi everyone, is there any way to find µncox and µpcox value in cadence, if so , do let me know, thanks in advance

Title: Re: How to find the process parameters
Post by raja.cedt on Dec 23^rd, 2011, 5:02am

hello,
are you a college grad?, you can find but whats the use of finding those parameters. becaz you don't know what the vgs-vth power in the id equation. Any please refer alpha power modeling by sakurai, you get some knowledge in this regard.

Thanks,
RAJ.

Title: Re: How to find the process parameters
Post by loose-electron on Dec 23^rd, 2011, 4:50pm

sri.sagar wrote on Dec 22^nd, 2011, 10:59pm:

Hi everyone, is there any way to find µncox and µpcox value in cadence, if so , do let me know, thanks in advance

It is buried in the transisor models in some cases.
(depends on the transistor models)

Another method is to use a set of transistor bias curves
and reverse engineer them out of there.

As a general rule, these don't get used too much
except as an academic illustration.

Title: Re: How to find the process parameters
Post by sri.sagar on Dec 26^th, 2011, 3:11am

thanks for the reply , I am doing my internship in analog design and i did reverse engineering considering CS stage as an exapmle and i got Mncox = 132u and Mpcox=32u for 90nm technology. i am not sure whether it's correct or not, if anybody knows the process parameters (Mncox and Mpcox) values for a particular technology/any other technology please let me know, so that i can compare my values.

and one more question is that , will the above parametes increases or decreases as the technology shrinks ?

Title: Re: How to find the process parameters
Post by raja.cedt on Dec 26^th, 2011, 3:33am

hello,
most of the times it increases (from theory point of view).
One thing i want suggest is if you want to continue in circuit design better start use gm/id method rather than struggling with finding about process parameters.
you can refer ee214 lectures notes by Boris murmon

Thanks,
raj.

Title: Re: How to find the process parameters
Post by RobG on Dec 26^th, 2011, 8:11am

sri.sagar wrote on Dec 26^th, 2011, 3:11am:

Small devices physical are so dependent on width and length that I would suggest a simulation where you sweep width for a few lengths to "measure" whatever parameter you are interested in. You should be able to also find some information on this in the process documentation.

The last 180nm process I worked in also had μ_nCox ≈ 4*μ_pCox. According to the textbooks it should be about 3x so I'd be very interested in why this is.

rg

Title: Re: How to find the process parameters
Post by sri.sagar on Dec 26^th, 2011, 9:25pm

Here is the way which i had followed, and correct me if I am wrong as am a newbie to this analog field

Steps to calculate µncox value in cadence

1). Consider a CS stage
Assume gain Av = 5v/v, RD = 10k, ID = 100µA, µncox = 150µ
Gain AV=gm RD
gm = AV / RD
gm = 5/10k = 0.5mƱ

But

gm = sqrt (2 µncox (W/L) n ID)
(W/L) n = 8.33 ≈ 10

So set W=10µ and L=1µ

After simulation, the gain(new) AV = 5.2 ≈ 5 (initially assumed)
gm(new) = 541.3 µ ≈ 0.5m (initially assumed) and ID(new) = 111µ

Based on gm (new), ID (new) and (W/L) n (old), we can calculate µncox as
gm = sqrt (2 µncox (W/L) n ID)
µncox = gm2/ (2(W/L) n ID)

µncox=132µ

The procedure remains same for µpcox and i got the value as

µpcox=32µ

Title: Re: How to find the process parameters
Post by ywguo on Dec 27^th, 2011, 12:41am

Hi sri.gagar,

Have you plot I-V curve of nmos and pmos transistors? Are you sure those MOS's follow square law rule for that 90nm CMOS technology? If NOT, do the parameters μncox and μpcox you derived fit all MOS widths/lengths in your design? You'd better simulate Gm/Id suggested by Raj and sweep width for a few length suggested by RobG. Please open the following link for some references about Gm/Id.
http://www.designers-guide.org/Forum/YaBB.pl?num=1299031733/4#4

Yawei

Title: Re: How to find the process parameters
Post by raja.cedt on Dec 27^th, 2011, 2:13am

hello sri.sagar,
in your post you have calculated gm by normal square law which is true only above 180nm (some rough number), which is gives very wrong results with 90nm and below. I strongly encourage you to proceed with gm/id, if you are still interested to do by this kind of calculation fist find the power of the Vgs-Vth in the current expression, for this refer

http://dit.upc.es/lpdntt/biblio/BREUS/SAK90a.pdf

Thanks,
raj.

Title: Re: How to find the process parameters
Post by sri.sagar on Dec 27^th, 2011, 10:26pm

thank you, it helped me a lot