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About various levels of spice models

Hello,

My question is regarding an ac small signal equivalent circuit and
spice models (level3, BSIM etc).


The complete MOS small signal model (i.e. with caps Cgb, Cgs, Cgd, Cbs,

Cbd, current sources gm*vgs, gmb * vbs, and output resistance rds).


Is the above small signal eqvt circuit valid only upto spice level 3
models or will the same small signal equivalent circuit also hold when
a BSIM or hspice level 28 model is used?


Do the advanced mos models (BSIM etc) have more compilecated small
signal eqvt circuit than the one mentioned above. where can I find it?


Thanks.


-Almitra P.
 
J

Jim Thompson

Jan 1, 1970
0
Hello,

My question is regarding an ac small signal equivalent circuit and
spice models (level3, BSIM etc).


The complete MOS small signal model (i.e. with caps Cgb, Cgs, Cgd, Cbs,

Cbd, current sources gm*vgs, gmb * vbs, and output resistance rds).


Is the above small signal eqvt circuit valid only upto spice level 3
models or will the same small signal equivalent circuit also hold when
a BSIM or hspice level 28 model is used?


Do the advanced mos models (BSIM etc) have more compilecated small
signal eqvt circuit than the one mentioned above. where can I find it?


Thanks.


-Almitra P.

You need to read your manuals/text books.

...Jim Thompson
 
Hi,

I understand that the more advanced the spice model (BSIM compared to
level 1,2,3), more detailed equations are used to obtain a better
accuracy. Also lower level models become inaccurate as device sizes
shrink.

My question is related to the small signal equivalent circuit.

Whether I use a level 3 model or a BSIM derived model, is it still ok
to use the same small signal equivalent circuit.

If you can suggest where can I find the answer that would be useful.

Regards,
-Almitra
 
Hi,

Some more information about my question.....

The reason that I asked the question is:

Refer to:
http://documents.wolfram.co.jp/applications/insydes/Appendix/MOSField-EffectTransistor.html

The small signal schematic shown for ac analysis using spice level 1-3
and the schematic shown for higher spice levels is different.

I was not able to understand the extra elements in the BSIM related
schematic and hence the question.

Regards,
Almitra Pradhan.
 
J

joseph2k

Jan 1, 1970
0
Hi,

Some more information about my question.....

The reason that I asked the question is:

Refer to:
http://documents.wolfram.co.jp/applications/insydes/Appendix/MOSField-EffectTransistor.html

The small signal schematic shown for ac analysis using spice level 1-3
and the schematic shown for higher spice levels is different.

I was not able to understand the extra elements in the BSIM related
schematic and hence the question.

Regards,
Almitra Pradhan.

It looks to me that they are modeling the voltage dependant capacitances as
complex G sources. (With what seems to be a little help from LaPlace
transforms.)
 
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