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Simulators >> Circuit Simulators >> DC Operating parameters in cadence results windows
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Message started by eng on Apr 3^rd, 2007, 11:38am

Title: DC Operating parameters in cadence results windows
Post by eng on Apr 3^rd, 2007, 11:38am

Hi all,
Can anyone tell me how I can find what all the abbreviations used for DC OP parameters in Results Display Window stand for. That is the window poping up when you do a DC analysis with spectre and print the DC Operating Parameters. Some of them are explicit by their names i.e. gm ids but others are not i.e. lv.. lx... .

I also need to find the channel length modulation constant. Is it written somewhere in this window?

Finally some of the cap values have minus sign what does this mean? what are the cgg cbb cgg?

thanks in advance
eng

Title: Re: DC Operating parameters in cadence results win
Post by Geoffrey_Coram on Apr 4^th, 2007, 7:44am

What sort of device are you using? I don't recognize Iv nor Ix from any MOS model I'm familiar with. Generally, one finds out what the values mean by:

spectre -help bsim3v3

(replace "bsim3v3" with your model name ...)

Note that the capacitances are defined in Spice to be
Cxy = - dQx / dVy for x != y
Cxx = dQx/dVx

So, cgg is the change in gate charge with respect to the gate voltage (holding all other voltages constant).

Title: Re: DC Operating parameters in cadence results win
Post by eng on Apr 4^th, 2007, 12:00pm

I'm using nfetx device from IBM .18um RF process and printing DC OP params thru Results -> Print -> DC Operating Points in Virtuoso ADE

Title: Re: DC Operating parameters in cadence results win
Post by Geoffrey_Coram on Apr 5^th, 2007, 5:32am

eng wrote on Apr 4^th, 2007, 12:00pm:

I'm using nfetx device from IBM .18um RF process

That's not quite what I meant; somehow you need to figure out what the underlying model is: bsim3v3, bsim4? You'll have to find the library files and search through them, or maybe if you can find the spectre log file (spectre.out) it should give you a count of all the elements in your circuit (# resistors, # capacitors, # bsim3v3, etc.)

Title: Re: DC Operating parameters in cadence results win
Post by eng on Apr 5^th, 2007, 12:12pm

I checked the spectre model file (.scs). it is BSIM3v3.2.4

Title: Re: DC Operating parameters in cadence results win
Post by Geoffrey_Coram on Apr 6^th, 2007, 3:27am

So, my guess "spectre -help bsim3v3" is correct. But I don't see Iv or Ix in the help output.

Title: Re: DC Operating parameters in cadence results win
Post by Andrew Beckett on Apr 11^th, 2007, 7:48am

In recent versions of spectre (MMSIM60 USR2 onwards, I think), you can also use some aliased names (for hspice compatibility) - the lv/lx names. So the help nowadays says things like:

Code:

19 cjd (F) Drain-bulk junction capacitance (alias=lx29).
20 cjs (F) Source-bulk junction capacitance (alias=lx28).
21 qb (Coul) total bulk charge (alias=lx12).
22 qg (Coul) Total gate charge (alias=lx14).
23 qd (Coul) Total drain charge (alias=lx16).
24 qbd (Coul) Drain-bulk charge (alias=lx24).

That said, I don't think it outputs these lx/lv parameters unless you specifically ask for them - perhaps it did at some point in the past (I only checked quickly just now).

Regards,

Andrew.

Title: Re: DC Operating parameters in cadence results win
Post by Geoffrey_Coram on Apr 12^th, 2007, 4:32am

Oh! I can't tell the difference between "Ix" (capital-i x) and "lx" (lowercase-L x).

I wonder if you get the lv/lx outputs if you use simulator lang=spice ...