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ams vs. spectre - incorrect results

Hello cadence users,

I am using C18 CMOS c18a6 technology from AMS - AG hitkit v.ams_4.11. The problem is with different/incorrect results for simulation instance 'sblkndresx' from library esd7rf. It's ESD protection contained in standard digital IO pad 'IOPAD1V8_3'.

Specifically the current flowed to the substrate is with spectre ~5.14pA - reasonable result. With ams simulator is ~1.78uA - incorrect result. Please see screenshot. This current is only current flowed to instance pin 'D'!

The question I would like to have answer is: What model is used by ams simulator? The only spectre model I found is 'sblkndres.scs'. This file is used by spectre simulator - I observed the changes for simulation results(Rsub increased etc.) But no change with ams simulator.

At this point I am not able to simulate chip with padring (IO pads) by ams simulator. Am I wrong or the model for 'sblkndresx' is really incorrect? The result is the same for IC6.1.5 and IC6.1.6 as well.

Thank you very much for the response in advance.

Best regards, Zdenko

Andrew Beckett over 11 years ago

Hi Zdenko,
The actual models ought to be the same between the two, but it's possible that the PDK setup is looking at the wrong terminal when reporting the current. It's very hard to know without being able to see the data and the PDK. So please contact customer support. Then an AE can take a look at the issue in more detail.
Kind Regards,
Andrew.
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Zdeno over 11 years ago

Thank you Andrew for quick answer, I will contact customer support.
Best regards, Zdenko
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Zdeno over 11 years ago

Hi Andrew,
I got answer from Cadence representative.
There are bugs in both Virtuoso and PDK. The circuit is netlisted differently depending on which netlister is used. Cellview-based netlister gives wrong results while OSS-based netlister gives correct result.
Best regards,
Zdenko
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Andrew Beckett over 11 years ago

Zdenko,
do you have a case number? I'm interested as to why this would be partly a virtuoso bug - I'm surprised. I'd like to take a look.
Andrew
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Zdeno over 11 years ago

Hi Andrew,
sorry for late response. The answer was exactly from Europractice who made request to AMS and Cadence so not directly from Cadence therefore I don't know case number.
Best regards,
Zdenko
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Andrew Beckett over 11 years ago

Thanks Zdenko.
I can't find anything reported to us from Europractice that looks like this (at least not recently), but maybe they've not reported it yet or did so via an informal channel.
Anyway, at least you have a route that works.
Kind Regards,
Andrew.
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