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Modeling >> Behavioral Models >> VHDL-AMS + Spice
https://designers-guide.org/forum/YaBB.pl?num=1187007970

Message started by adauto6 on Aug 13^th, 2007, 5:26am

Title: VHDL-AMS + Spice
Post by adauto6 on Aug 13^th, 2007, 5:26am

I'm trying to do ac analysis using VHDL-AMS + Spice with Eldo and ADMS. I already put the AC Stimulus but the simulator give me the error:
"
# #E Error: Nul parameter in function LOG()
# Occurred at frequency 1000 Hz
"

Title: Re: VHDL-AMS + Spice
Post by Geoffrey_Coram on Aug 15^th, 2007, 8:57am

Have you checked your VHDL-AMS model for proper use of the LOG() function? (Does it use the function? Can you print the value of the argument?)

Title: Re: VHDL-AMS + Spice
Post by adauto6 on Aug 15^th, 2007, 11:57am

I use the function exp() twice but their don't appear to be the problem because the DC analysis use the same function with the same argument and don't return the any error like it.

Title: Re: VHDL-AMS + Spice
Post by Geoffrey_Coram on Aug 16^th, 2007, 8:10am

And you don't use log() or log10() anywhere in your VHDL-AMS?

Does your simulator compute some gain automatically? Did you define an output signal, so maybe it's trying to compute db and the input never makes it to the output? Vdb(out) = 20 * LOG(V(out) / (input ac magnitude)) perhaps?

Title: Re: VHDL-AMS + Spice
Post by adauto6 on Aug 16^th, 2007, 11:08am

I'm using the function log ...but the DC and Tran simulation don't return Error ...so the argument into the log function is the problem only when i run the AC analysis.

Do i have to put one model to do the AC analysis and other to do the DC e TRAN analysis ??
doing it with the condition:
if domain = quiescent_domain or domain= time_domain use
...
else
.... AC model
end use;

Title: Re: VHDL-AMS + Spice
Post by Geoffrey_Coram on Aug 16^th, 2007, 11:29am

adauto6 wrote on Aug 16^th, 2007, 11:08am:

Do i have to put one model to do the AC analysis and other to do the DC e TRAN analysis ??

I'm not very familiar with VHDL-AMS, but I strongly discourage people from doing that sort of hackery when writing Verilog-AMS models. The simulator should do the linearization of the model for use in ac analysis, in order to ensure consistent ac and transient results.

Title: Re: VHDL-AMS + Spice
Post by adauto6 on Aug 16^th, 2007, 11:46am

There are any problem running AC analysis with log function ??

Title: Re: VHDL-AMS + Spice
Post by Geoffrey_Coram on Aug 17^th, 2007, 4:48am

adauto6 wrote on Aug 16^th, 2007, 11:46am:

There are any problem running AC analysis with log function ??

Shouldn't be. log has a well-defined derivative everywhere it has a value (x>0). Have you tried putting log() in a simpler model?

Title: Re: VHDL-AMS + Spice
Post by adauto6 on Aug 17^th, 2007, 10:38am

No ... but when a delete all log function on my code ..and inside my log function there aren't null parameter ... i know that because my DC analysis runs very well. ..