The Designer's Guide Community
Forum
Welcome, Guest. Please Login or Register. Please follow the Forum guidelines.
Oct 20th, 2020, 4:09pm
Pages: 1
Send Topic Print
Questions about MOS device noise model... (Read 9714 times)
zhangjerome
Community Member
***
Offline



Posts: 42

Questions about MOS device noise model...
Jan 21st, 2007, 6:25pm
 
How do the noise parameters such as alpha (gm/gd0) and gamma (channel thermal noise coeffecient) related to BSIM3 model?

Now my PDK is based on BSIM3. But generally the manual calculation is based on noise parameter such as alpha and gamma.  How to derive these parameters from BSIM3 model?

And another question. Since BSIM model doesn't represent the gate induced noise, which is very important in LNA design, I want to know that how to take into account the gate induced noise in simulation.

Thank you guys

Regrads,

Jerome Zhang.
Back to top
 
 
View Profile   IP Logged
ACWWong
Community Fellow
*****
Offline



Posts: 539
Oxford, UK
Re: Questions about MOS device noise model...
Reply #1 - Jan 22nd, 2007, 3:09am
 
BSIM3 allows for a choice of noise (flicker & thermal) model equations, based on what the noimod value is (1 to 4).
noimod=1 is SPICE based, so will be pretty familiar to you.
noimod=2 is BSIM3 based, so a bit more involved.
noimod=3 is mixture of BSIM filicker noise & SPICE thermal.
noimod=4 is mixture of SPICE flicker and BSIM thermal.
So my advice for you is to check out your model files to see the noimod you are using. Then just do a google search (or search your simulation tool model guide) to find the equations, for which you can do hand calculations if required. If you are using BSIM noimod, then I would suggest hand calcluations may be rather cumbersome.

Addition noise paramters for high frequency MOS are either in built into the model card or not depending on your PDK. If you have a simulation/measurement graphs which correlate the modelling upto your frequency of interest (as you would expect in an RFCMOS PDK) then you are lucky. Otherwise you may need to add additional components into your design mimic additional noise contributors. Typically I add gate, bulk and source/drain resistors, whose value depends on layout. Additional modelling for gate induced shot noise (very very small) and NQS may or may not be relevant to your design as well.

cheers
aw
Back to top
 
 
View Profile   IP Logged
zhangjerome
Community Member
***
Offline



Posts: 42

Re: Questions about MOS device noise model...
Reply #2 - Jan 22nd, 2007, 11:03pm
 
aw, thank you very much for your patience.

Now The PDK I am using is based on BSIM3v3 model. I know it's difficult to calculate the noise manually from the given model parameters. Since the noise power of a MOS is equal to 4kT*gamma *gd0 and alpha=gm/gd0, I am wondering whether I can derive alpha and gamma from BSIM models? Are there any formulas between them?

My PDK does provide noise report for flicker noise but the parameters such as Noia, Noia are not contained in the model files. To include the flicker noise in the model, should I just add these parameters into the model files?

And, I think the BSIM thermal noise doesn't contain gate induced noise. Is it right?

Thank you~~

Regards.

Jerome Zhang
Back to top
 
 
View Profile   IP Logged
Geoffrey_Coram
Senior Fellow
******
Offline



Posts: 1986
Massachusetts, USA
Re: Questions about MOS device noise model...
Reply #3 - Jan 23rd, 2007, 6:10am
 
zhangjerome wrote on Jan 22nd, 2007, 11:03pm:
Now The PDK I am using is based on BSIM3v3 model. I know it's difficult to calculate the noise manually from the given model parameters. Since the noise power of a MOS is equal to 4kT*gamma *gd0 and alpha=gm/gd0, I am wondering whether I can derive alpha and gamma from BSIM models? Are there any formulas between them?


No.  gamma is an excess noise factor; usually one has 8/3 kT (gm + gds + gmbs), and the gamma allows the foundry to modify this.  It's not something you can derive from other parameters.

Quote:
My PDK does provide noise report for flicker noise but the parameters such as Noia, Noia are not contained in the model files. To include the flicker noise in the model, should I just add these parameters into the model files?


Noia, Noib, Noic are only used for the BSIM3 noise model; KF and AF are used for the Spice2 noise model (see AW's post).  What is the value of NOIMOD in the model card?  The default is 1.

Quote:
And, I think the BSIM thermal noise doesn't contain gate induced noise. Is it right?


That's correct.
Back to top
 
 

If at first you do succeed, STOP, raise your standards, and stop wasting your time.
View Profile WWW   IP Logged
zhangjerome
Community Member
***
Offline



Posts: 42

Re: Questions about MOS device noise model...
Reply #4 - Jan 23rd, 2007, 5:00pm
 
Coram:

Thank you.

My PDK is based on BSIM3 so noimod=2. The foundry give me a noise report and parameters such as noia and noib but these parameters are nod included in the modle files. So should I just add these parameters into the model files to include its effect??

Regards.

Jerome Zhang
Back to top
 
 
View Profile   IP Logged
Geoffrey_Coram
Senior Fellow
******
Offline



Posts: 1986
Massachusetts, USA
Re: Questions about MOS device noise model...
Reply #5 - Jan 24th, 2007, 3:57am
 
zhangjerome wrote on Jan 23rd, 2007, 5:00pm:
My PDK is based on BSIM3 so noimod=2. The foundry give me a noise report and parameters such as noia and noib but these parameters are nod included in the modle files. So should I just add these parameters into the model files to include its effect??


You should add noia, noib, noic.  There are a couple other parameters (lintnoi, em) that can be used to tune the answer.  The noi? parameters all have default values that should cause some 1/f noise even if there's nothing in the model card (in noimod=1, kf=0 is the default, so you get no 1/f noise).

Just to be clear: the BSIM3 model code includes the equations for the older Spice2 noise model; just because the PDK uses BSIM3 doesn't mean that they are using the BSIM3 noise model.  I suspect that you are actually getting noimod=1 (the default value of noimod) if you aren't presently seeing any 1/f noise.
Back to top
 
 

If at first you do succeed, STOP, raise your standards, and stop wasting your time.
View Profile WWW   IP Logged
ACWWong
Community Fellow
*****
Offline



Posts: 539
Oxford, UK
Re: Questions about MOS device noise model...
Reply #6 - Jan 24th, 2007, 4:39am
 
Jerome,
Geoffrey is correct you must inspect your model file to see what noimod is set to, NOT just assume.
Why don't you do some simulation and compare it with the measuement data the foundry supplied to see if you have a problem of not ?
In the case where noise is not modelled in you devices, it is not really sensible for you to "make a guess" and add them yourself. You must ask your foundry first for information.
cheers
aw
Back to top
 
 
View Profile   IP Logged
zhangjerome
Community Member
***
Offline



Posts: 42

Re: Questions about MOS device noise model...
Reply #7 - Jan 24th, 2007, 5:12pm
 
Thank you two, Geoffrey and AW...

Regards

Jerome Zhang
Back to top
 
 
View Profile   IP Logged
Pages: 1
Send Topic Print
Copyright 2002-2020 Designer’s Guide Consulting, Inc. Designer’s Guide® is a registered trademark of Designer’s Guide Consulting, Inc. All rights reserved. Send comments or questions to editor@designers-guide.org. Consider submitting a paper or model.