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Other CAD Tools >> Entry Tools >> Transient ---> Save--->AC
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Message started by rajdeep on Oct 30^th, 2008, 10:15am

Title: Transient ---> Save--->AC
Post by rajdeep on Oct 30^th, 2008, 10:15am

Hi all,

I have a requirement as follows:

Step 1: I need to run transient analysis upto a certain point and save all the
node voltage and current.

Step 2: Feed those values as the initial condition for the next analysis which
is ac analysis.

I am using Cadence Spectre.
I am particularly worried abt the 2nd step, however not sure how to do any of these steps.

Any ideas guys?

Rajdeep

Title: Re: Transient ---> Save--->AC
Post by Ken Kundert on Oct 30^th, 2008, 12:54pm

The basic idea would be to run the transient first, and then run the AC analysis with restart=no. I don't know that you can do this within Artist as Artist constrains the analysis order and may do the transient last, but you can certainly do it when running Spectre outside of Artist by just putting the AC analysis after the transient analysis in the netlist.

It might also be possible to use some combination of writefinal in the transient analysis and readforce and skipdc in the AC analysis, but again if you try this in Artist you might end up getting the final transient point from your last simulation because Artist probably runs the transient last.

-Ken

Title: Re: Transient ---> Save--->AC
Post by rajdeep on Oct 31^st, 2008, 3:10am

Thanks Ken.

It worked. Artist actually did the tran first, then skipped the dc and did the ac analysis (as I
gave restart = no) hopefully from the last saved operating point of the transient analysis.

But the results look a bit odd!! Is there a way to check with what initial conditions an
ac analysis starts?

Also, there is an option called store/restore. But seems like it does not work on ac!!

Thanks!
Rajdeep

Title: Re: Transient ---> Save--->AC
Post by Ken Kundert on Oct 31^st, 2008, 11:17am

You can use writefinal on the transient. Perhaps write on the ac might work as well.

-Ken

Title: Re: Transient ---> Save--->AC
Post by Tlaloc on Nov 6^th, 2008, 2:33pm

The way that I do this in Artist is to chose tran->Options. Towards the bottom of the screen are two fields called actimes and acnames. actimes are the points you want the AC run at, and acnames specifies the analysis type, e.g. ac, stb, or xf. This sometimes saves the transient operating point in the "normal" way, but it seemed a little flaky to me in the past. Because of that, I normally copy the same times in actimes to the infotimes field. That always works properly with back-annotating the operating points and node voltages at those times in the Composer window.

Title: Re: Transient ---> Save--->AC
Post by microant on Dec 4^th, 2008, 12:32am

Hi Rajdeep

You can run AC analysis alonely.
first, in the 'initial condition...' add the init value for the net,
then, in the option for AC analysis, setup with force=all, oppoint=logfile, restart=no.
after this, you can run the simulation and the OP info you will see in the output log.

BR,
Lin

Title: Re: Transient ---> Save--->AC
Post by Andrew Beckett on Jan 2^nd, 2009, 11:51pm

Also, for Ken's information, ADE does allow the order of the analyses to be specified. Under Setup->Environment, there's a field "Analysis Order" which you can enter (say) "dc tran ac" (the names of the analyses in the order you want them) to override the default order.

Regards,

Andrew.

Title: Re: Transient ---> Save--->AC
Post by Ken Kundert on Jan 3^rd, 2009, 8:25pm

Thanks Andrew.

-Ken