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HBAC possible bug? Not saving capacitor current

AncisMichele over 3 years ago

Hi,

I wanted to save a current through a cap for an HBAC following an HB.

This current is saved by HB, but not by HBAC. Have I stumbled into some bug or am I doing something wrong?

I've worked around the issue by placing an explicit current probe, however I'm just curious.

Regards,

Michele

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Andrew Beckett over 3 years ago

Michele,

No, it's not a bug. For saving built-in terminal currents of a number of devices in AC analyses you need to set the useprobes option on the Outputs->Save All form:

Andrew
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Andrew Beckett over 3 years ago

Michele,

No, it's not a bug. For saving built-in terminal currents of a number of devices in AC analyses you need to set the useprobes option on the Outputs->Save All form:

Andrew
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AncisMichele over 3 years ago in reply to Andrew Beckett

Thanks Andrew!

Amazing I never noticed that in 20 years

Regards,

Michele
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Tawna over 3 years ago in reply to Andrew Beckett

Hi Andrew and AncisMichele,

You never want to set useprobes=yes for RF analyses. It can cause errors in small signal (hbac, hbnoise, etc.) results. useprobes should only be used for linear ac results. Reference: Getting the Most Out of Spectre® APS RF 21.1: Maximizing Performance page 17 or Getting the Most Out of Spectre® X-RF 21.1: Maximizing Performance page 74.
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AncisMichele over 3 years ago in reply to Tawna

Wow, thanks Tawna.

So, in the end of the day, to have the current of a capacitor in an HBAC simulation I need to resort to an explicit probe, is that right?

Thanks,

Michele
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Andrew Beckett over 3 years ago in reply to AncisMichele

Hi Michele,

We've been having some discussions about this. The main concern with using useprobes=yes with RF simulation is that if you are asking to save a lot of currents, then this could impact the performance because it causes an iprobe to be automatically added in series with each terminal for which you are saving currents. That would increase both memory and performance and potentially convergence, but it's not clear that this would lead to accuracy issues unless there was a big convergence problem.

R&D are of the view that this should be OK to use with small numbers of selected currents being saved, and the information in the documentation is probably out-dated and I've suggested that we clarify the statements to make it more focused on the memory/performance issues rather than it being an accuracy issue.

Regards,

Andrew
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