Small signal analysis during transient, triggered by event

Dear Steven,

StevenMikes said:

For example, say I would like to run an AC sim when a particular voltage crosses 0.

Have you explored the actimes feature of spectre? This allows you to perform an AC small signal analysis at specific times of a transient simulation as it is progressing. A couple of articles that detail this capability (depending on how you are perfoming the simulation) are at URL:

https://support.cadence.com/apex/ArticleAttachmentPortal?id=a1Od0000000nSkaEAE&pageName=ArticleContent&oMenu=People%20who%20viewed%20this%20also%20viewed

https://support.cadence.com/apex/techpubDocViewerPage?xmlName=anasimhelp.xml&title=Virtuoso%20Analog%20Design%20Environment%20L%20User%20Guide%20--%20Setting%20Up%20an%20Analysis%20-%20Transient%20Analysis&hash=pgfId-1013885&c_version=IC6.1.8&path=anasimhelp/anasimhelpIC6.1.8/chap5.html#pgfId-1013885

(do a "find" for "actimes" in this latter URL)

Does this address your question Steven or did I misunderstand your question?

Shawn

Shawn, I'm afraid you may have misunderstood. As I said at the beginning of my post, I already know how to run small signal analyses at predetermined times using actimes.

What I'm asking is if there is a way to run small signal analyses based on events in the simulation, which could occur at any time. My example was a small signal AC analysis triggered by a particular voltage crossing 0. The time of the zero crossing is not known beforehand.

Dear Steven,

My apologies for not fully understanding your question! In short, the answer is yes to your question. You may trigger an ac small-signal analysis during the course of a transient analysis through the use of an assertion. Please refer to the following for some instructions and an error you may encounter if your version of spectre is not current.

https://support.cadence.com/apex/techpubDocViewerPage?xmlName=spectreuser.xml&title=Spectre%20Classic%20Simulator,%20Spectre%20APS,%20Spectre%20X,%20and%20Spectre%20XPS%20User%20Guide%20--%20Analyses%20-%20Performing%20Event-Triggered%20Analysis%20During%20Transient%20Analysis&hash=pgfId-885296&c_version=19.1&path=spectreuser/spectreuser19.1/chap7.html#pgfId-885296

https://support.cadence.com/apex/ArticleAttachmentPortal?id=a1O0V0000091CU1UAM&pageName=ArticleContent

Hopefully, I did a better job this time!! Sorry!

Shawn

Hi Shawn,

You beat me to it! I was just about to quickly suggest the following steps (using SPECTRE17.1 or later):

1. Create a file called (say) myTrigger.scs with contents similar to the following:
   sigoutCross assert expr="V(sigout)" max=0.0 // the signal you want and the threshold you want
2. Reference this via Setup->Model Libraries in ADE
3. In the actimes field of tran analysis, enter @sigoutCross (which will trigger on the first crossing) or "@(sigoutCross,2)" if you want the second crossing, or "@(sigoutCross,0)" if you want all crossings (note, you need the quotation marks if you have the event in parentheses such as this).
4. Fill in the acnames as "ac" and set up the ac analysis as usual.

In addition to triggering on an assert, you can trigger on a variable changing in a Verilog-A model (this is useful if you need more precision for the threshold crossing; asserts do not force a timestep at the threshold crossing, whereas using @cross in VerilogA can do that).

Regards,

Andrew

The error described in https://support.cadence.com/apex/ArticleAttachmentPortal?id=a1O0V0000091CU1UAM&pageName=ArticleContent does not depend on the Spectre version, but on the Virtuoso version, which is responsible for the netlisting. The error was fixed in the IC6.1.8 ISR3 and ICADVM18.1 ISR3 releases.

Brilliant, thank you gentlemen!