The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> hspice model file noise factor
https://designers-guide.org/forum/YaBB.pl?num=1135755424

Message started by neoflash on Dec 27^th, 2005, 11:37pm

Title: hspice model file noise factor
Post by neoflash on Dec 27^th, 2005, 11:37pm

My hspice model file does not contain noise parameter: AF KF.

However, it specified parameter: noimod=2.

When I do simulation of noise, I could see flicker noise. However, I am not sure how simulator knows
transisors' noise performance?

Title: Re: hspice model file noise factor
Post by Andrew Beckett on Jan 2^nd, 2006, 10:47pm

You didn't say what model it is you're using. Various models (such as bsim4) have
other parameters for specifying flicker noise. For example in spectre's bsim3v3
implementation:

Code:

Noise model parameters:
196 noimod=1 Noise model selector.
197 kf=0 Flicker (1/f) noise coefficient.
198 af=1 Flicker (1/f) noise exponent.
199 ef=1 Flicker (1/f) noise frequency exponent.
200 noia=1e20 Oxide trap density coefficient. Default is 9.9e18 for pmos.
201 noib=5e4 Oxide trap density coefficient. Default is 2.4e3 for pmos.
202 noic=-1.4e-12 Oxide trap density coefficient. Default is 1.4e-8 for pmos.
203 noid=2e14 flicker noise subthreshold-above threshold transition coefficient.
204 wnoi=1e-5 m Channel width at which noise parameters were extracted.
205 em=4.1e7 V/m Maximum electric field.
206 flkmod=0 Flicker noise model (0 for Ids based model, 1 for gm based model).
207 gamma=2.0/3.0 Thermal noise coefficient.
208 nlev=2.0 49 noise selector.
209 gdsnoi=1.0 Channel thermal noise coefficient for 49 noise.

Parameters noia,noib,noic etc would also suffice to cause flicker noise.

Check the documentation for the model you're using; there may be different parameters
controlling the noise (bsim4 has this too, for example).

Regards,

Andrew.

Title: Re: hspice model file noise factor
Post by Geoffrey_Coram on Jan 3^rd, 2006, 5:31am

NOIMOD=2 is from BSIM3, and uses with NOIA, NOIB, NOIC.

I find Andrew's post a little misleading:

Quote:

Parameters noia,noib,noic etc would also suffice to cause flicker noise.

If NOIMOD=1 or 4 (or 5), then NOIA, NOIB, NOIC will have no effect at all. If NOIMOD=2 or 3
(or 6), then NOIA, NOIB, NOIC are used, and they have non-zero default values, so you may or may
not find the value in the model card (though the defaults are unlikely to be correct for your process).

(NOIMOD=5 and 6 were added in BSIM3 version 3.3 and make a slight change to the thermal noise model
relative to NOIMOD=1 and 3, respectively.)

Title: Re: hspice model file noise factor
Post by Andrew Beckett on Jan 3^rd, 2006, 9:27pm

Geoffrey is quite right, of course. I wrote my post in a hurry and didn't make it as clear as I should have. Because you'd said that you had noimod=2 in the model file, I'd made some assumptions, but the real point of my post was that flicker noise is not just controlled by kf, af etc.

Regards,

Andrew.