Transient results as starting point in PSS

Prakash,

Both PSS and tran have a capability to "save" and "recover" the state at the end of (or arbitrary points throughout) a transient. There are parameters "saveperiod", "savetime", "saveclock", "savefile" and "recover" for this. These save the entire state and can be restarted reliably from where it left off. Unfortunately you can't use a save file from transient in PSS or vice versa - you can only use them in the same analysis.

The alternative is a less perfect solution which you might be able to get away with but has to be used with care. On the transient use "writefinal" to save a final nodeset/ic file. Then on the PSS use "readic" to point to that filename, and set skipdc=yes - but allow enough time for any imperfections to settle out. Since this doesn't capture quite everything, sometimes it needs some time to get over initial discontinuities caused by the missing information in the ic file.

Regards,

Andrew.

Hi Andrew, 

In ADE Assembler I am using transient results from "Writefinal" as a starting point for my PSS sims "readic". I specify a file location/name for witefinal and use the same location/name in redic and that seems to be working when I run nominal corner. When I try to run multiple corners I only get one writefinal file which correspond to the last transient corner that finished. Is there a way to save "Writefinal" per corner in transiant sim and use that data as a starting point for the corresponding PSS sim?

Best,

Hamed

Dear Hmjafari,

Hmjafari said:

When I try to run multiple corners I only get one writefinal file which correspond to the last transient corner that finished. Is there a way to save "Writefinal" per corner in transiant sim and use that data as a starting point for the corresponding PSS sim?

I am not Andrew, and will never hope or pretend to have the insight and knowledge he has! Nevertheless, have you tried using the methodology provided in the Cadence Sourcelink at URL:

https://support.cadence.com/apex/ArticleAttachmentPortal?id=a1Od0000000uDrGEAU&pageName=ArticleContent

for using a custom recover and restore file for snapshots? I assume this will work in Assembler, but can't say I have verified it. I have used it with a pss file in the former ADE-XL to save a re-run a pss analysis and has saved a lot of simulation time.

Shawn

Hi Hamed,

Regarding:  Is there a way to save "Writefinal" per corner in transiant sim and use that data as a starting point for the corresponding PSS sim?

I wanted to make sure that you realized this:  You cannot use transient results as in input to pss.  See my article:   Can I use a transient output as an input to pss or hb analysis instead of using tstab? 

You may want to look at this article:   Running multiple PAC (or PXF, Pstb, etc.) analyses from a single PSS analysis. 

Also see:  Spectre Circuit Simulator and Accelerated Parallel Simulator RF Analysis in ADE Explorer User Guide -- Single Input Large and Small-signal Analyses - Reuse Tab 

Best regards,

Tawna 

Thanks a lot Tawna, 

The reason I used transient sim "Writefinal" as initial condition for PSS is that transient  sim runs much faster compared to PSS for the same amount of tstab time setting. The pss results are used for pnoise and pxf sim.

I have a regulator + some low pass filter in my test-bench that force me to run pss tstab for ~2us. This take roughly 4-5 days on 4 core APS. Same 2us runs in few hours for transient sim (both use dynamic errpreset, liberal at start and conservative at the last 10% of sim time). 

In my test case, I first ran transient sim for 2us, then use the "writefinal" as the inital condition for pss. I set pss tstab for 100ns and it seems that pss is using that initial condition from transient sim and settling within 100ns. If this is a wrong flow as you described in your article, is there a way to speed up the pss tstab sim? That way I don't need to run transient sims at all. 

Thanks a lot for your helps. Much appreciated.

Best,

Hamed

Thanks a lot Sawn. 

Thanks a lot Sawn.