I have a question to ask about BSIM model, I hope it
will not take too much time for you to answer this question. Since now
I am using a BSIM3.3 0.18-um CMOS model in my work (Cadence, Spectre)
and I am wondering about how to figure out the total parasitic
capacitances of a transistor. In PSPICE, after I ran a simulation and
click on the Probe window to see the output file, I can see a list of
small-signal parameters saying that, for example, Cgs = 10 fF (for
intrinsic), Cgsov = 20 fF (for overlap capacitance), etc.
However, for BSIM3.3 and for Spectre simulator, I received a set of
small-signal parameters after running a simulation, for example, as
shown in the attached file. For these parameters, for the capacitances,
I don't know how to calculate the total intrinsic and extrinsic
capacitances since they are separated into several capacitances. Would
you mind to explain me a little bit about this ?
The complete set of spectre BSIM3v3 output operating point parameters can be found in the "Virtuoso Simulator Circuit Components and Device Models Manual"
After performing a DC operating point simulation and saving the results, you can use the results browser to select the dcOpInfo (or use print) and browse the available operating point information for a selected component. In my case, I do see "cgs" and "cgsovl" for BSIM3v3
Thank you very much for the information. I am having a look at the document you mentioned. However, it seems that I am not being able to figure out how to calculate the real intrinsic Cgs, for example. Did you really see Cgs, Cgsov parameters like this from Results --> Print --> DC operating point ?? For my case, as shown in the attached picture, my Cgs is negative and there are also Cgg, Csg, Cdd .., etc. So from this output data, I am very confused about how to calculate the effective value of, for example, intrinsic Cgs.
Would you mind to suggest again :)
You can refer to these links for explanations of the capacitances in BSIM model:
What version of spectre/MMSIM are you using? I am using spectre 7.1 (a fairly recent version) and get the following from Results --> Print --> DC operating point
signal OP("/I0/NM10" "??")
betaeff 282.703mcbb 50.9655fcbd -77.4215acbdbi 36.8578fcbg -24.7584fcbs -26.1297fcbsbi 48.289fcdb -4.34466acdd 36.929fcddbi -36.9323fcdg -36.9404fcds 15.8045acgb -24.097fcgbovl 265.891acgd -36.5642fcgdovl 36.926fcgg 186.958fcgs -126.297fcgsovl 36.926fcjd 36.9353fcjs 74.4187fcsb -26.8642fcsd -287.387acsg -125.259fcss 152.411fgbd 61.5137u...etc.
Thank you for the information. Actually, I already knew the meaning of negative capacitances. However, what I have never known is how to calculate the "effecitve" value of the capaictances. For example, in case that I would like to know the total intrinsic gate-source capacitance from the operating-point results, how could I do that ??? There are Cgs, Csg, Css, Cgg ... etc. How could I calculate the total Cgs using these parameters ???
By the way, thank you very much again,