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An error with Momentum S parameter blocks in Spectre

JoshK

Hi,

I have a design with Momentum blocks incorporated inside (as 'mom' blocks). All Momentum blocks are simulated up to 300GHz.

However, when running harmonic balance simulation, I get an error: "Can not enforce causality of S parameter for assigned 'fmax' value is equal to or less than the maximal frequency in...." where the rest is the path to the mommdl/text.txt file of the momentum cell view.

The maximal frequency of the HB simulation (100GHz) is far lower than the upprer simulated Momentum frequency (300GHz).

Any ideas on how to solve the problem?

Thanks. 

  • Tawna
    You didn’t mention your nport settings nor the version of spectre that you are using.

    Please provide that.  I suspect your nport settings are the issue.

    Also, I am assuming that your s-parameter files are in touchstone, CITI, or spectre format.  

    Best regards,
    Tawna
  • JoshK

    I am a newbie in the RF design area. 

    I do not use nport from analoglib, but rather simulate my layout in Momentun and then generate a schematic symbol from the Momentum tool. This block generated by Momentum has a 'mom' written inside. 

    When looking at the properties of this symbol, I can only see the maximal frequency, which is the maximal frequency I configured in Momentum. 

    How can I proceed debugging the problem? 

  • Tawna

    I can help with Spectre debugging...but not Momentum (I've not used Momentum).  Sorry!   However, note that the error message you reported is a Spectre error message. 

    For Momentum issues, you may want to contact the Momentum support folks. (This is a Cadence Community forum.)

     

    best regards,

     

    Tawna

  • Andrew Beckett

    Watch out if you're using the symbol generated by the Momentum interface rather than using an analogLib nport and referencing the s parameter file. From what I've seen recently at customers, the Momentum-generated symbol sets the maximum frequency to be the maximum frequency in the s parameter file, but this defeats the causality correction in spectre. So on the instance, set the maximum frequency to 3 times the value it shows (ie 3 times the frequency you solved up to in Momentum). This is the default value for the underlying nport - unfortunately the momentum symbol doesn't work if you just blank out the max freq in the form. 

    I've let Agilent know about this (I think I did anyway; I'll check my email when I get into work) 

     Also, please use MMSIM12.1 to get the latest improvements in spectre's nport component (needed for simulating a parameters)

     Regards,

     Andrew 

  • Frank Wiedmann

    By the way, to find out more about the improvements in the nport component mentioned by Andrew, take a look at /blogs/rf/archive/2012/11/19/spectre-rf-mmsim-12-1-preview-of-coming-attractions.aspx.

  • JoshK

    When I look at the properties fo the Momentum generated block ("Edit Object Properties"), all parameters are greyed out, and the only filled parameter is "ImpMaxFreq", which is set to the frequency up to which I solved in Momentum. However, I cannot change its value.

    How can I change the maximum frequency as you suggested?

    Thank you for the help.

  • Andrew Beckett

    Sorry, I wasn't sure whether the field was editable - I'll explain how I fixed it when I saw this in person.

    In the CIW, use Tools->CDF->Edit CDF, and set the  CDF type to "Base". Then pick the lib/cell of the Momentum generated block, and then you'll see all the parameters for the cell, including ImpMaxFreq. Change this to 3 times the value, and OK the form.

    Regards,

    Andrew.

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