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my PSTB magnitude plot shows just 0 dB DC Gain !!

Wavefunction

To begin with: Let me clarify that I'm using icfb 5.1.0 and spectre 7.1.1 for my simulations.

My circuit has an opamp which supplies the tuning voltage to the succeeding VCO stage. It has to be mentioned that a feedback path exists from the oscillator to the opamp and thus I set out to ascertain the stability of the feedback loop present. I'm making use of the pstb analysis with the iprobe component placed between the output of opamp and tuning input of VCO.

What puzzles me is that the loop gain magnitude from the pstb always starts from 0 dB!  But the entire circuit works fine displaying a good tuning curve. One more point to add is that the opamp is a behavioural model where I'm free to change its Gain and GBW.

I'm attaching the plot here and its unclear to me if I'm missing some basic understanding of the pss and pstb analyses.

Could anyone throw some light on this?

Thanks in advance! 

  • I'm afraid the image is not pinning up.

    Can't the url id in the add-image option point to a directory in my local machine?

    But I hope, you get the idea anyway regarding the pstb plot. 

  • Hi Wavefunction,

    If you try to add an image as a URL, it would need to be to somewhere accessible over the web. However, that's not needed - if you go to the Options tab (when replying to a post, or posting a new topic), you can add file attachments, including pictures.

    That said, I doubt very much that a picture of the graph would help. I think seeing the design would probably be needed to understand this. Given that you probably can't post that to a public forum, I would suggest contacting customer support via http://support.cadence.com

    Best Regards,

    Andrew.

  • Hi Andrew,

    Your posts through various forums have proved really useful on many occasions.

    Thank you for these suggestions and for your overall assistance  :-)

     

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