vcvs Impedance Dips in Frequency

Chris,

That looks like a numerical artefact given the size of the impedances. Can you do two things (to make it easier for a lazy person like me to test):

1. Tell me exactly which spectre subversion you're using (this should be at the top of the log file, or what "spectre -W" reports)
2. Post the input.scs from ADE so that I don't have to re-enter the schematic...

Thanks,

Andrew.

Please find  output below .

Cadence (R) Virtuoso (R) Spectre (R) Circuit Simulator
Version 13.1.1.252.isr11 64bit -- 14 Aug 2014
Copyright (C) 1989-2014 Cadence Design Systems, Inc. All rights reserved worldwide. Cadence, Virtuoso and Spectre are registered trademarks of Cadence Design Systems, Inc. All others are the property of their respective holders.
Includes RSA BSAFE(R) Cryptographic or Security Protocol Software from RSA Security, Inc.

input.scs file is attached. (The attachment window does not accept .scs files so renamed to .doc. The file itself is unchanged)

Please let me know if you need anything else. 

Many Thanks.

Chris.

input.doc

I ran with spectre version 16.1.0.440.isr8 (I changed R0 and R1 back to 1M too - after trying with 100K as you provided it and getting a similar shaped curve). I get:

I plotted using zpm('sp 1 1) which is the same function that the Z11 button in the Direct Plot form uses (in IC617 at least; I suspect it's been that way since at least some point in IC615).

So all looks OK with the world using this version, at least... I can only imagine it was a numerical problem that's now been resolved (unfortunately I'm sat in an airport so can't really check the older spectre version  you're using).

Can you try a newer spectre version?

Regards,

Andrew.

Hi Andrew,

Thanks for getting back so quickly (despite being stuck at the airport).

Since you thought it might be to do with impedance values, I have tried varying some of the C and L values and found the culprit to be C1 (decoupling cap of port1). Setting this value to 10uF I get exactly the same graph as yours above. I can change any other impedance (aside from C1) and still get the same (clean) Z11 but increasing C1 slowly brings back the artefacts and setting C1=1mF or higher is enough to recreate my Z11 (or zpm('sp 1 1) ) graph in the original post.

So this is great as it means I have a simple fix in all my test-benches now and 10uF decoupling is more than enough for the frequencies I am working with.

Unfortunately we haven't migrated our server to the latest tools yet but I will put in a reminder with the IT department and see where it goes. If you can think of any other settings in my current version of Spectre that might help then please let me know and I can try them out. Otherwise consider this case closed.

Many thanks for all your help with this.

Best Regards,
Chris.