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Calculate input impedance for matching with spectreRF

engrvip

Hi

I am designing an LNA and want to match its input impedance to 50Ohms port impedance.


During 'sp' analysis in spectreRF , which function will give me idea about this impedance matching.

Gp,Ga , Gmax ,Gumx etc.  only gives the gain value depending upon kind of matching at input and output of LNA.

Is it OK to use Z11 and Z22 as input and output impedance values for matching purpose.

Or is their some other way thru which impedance matching is determined in SP or some other analysis with spectreRF.

Regards

Vipul

  • Hi Vipul,

    There is a chapter in the SpectreRF User Guide that you should take a look at:  analogLib Components Used in RF Simulation.  You'll want to look at the port component, specifically terminating the port.

    Next, there is a section Reference:  S-Parameter Equations.  These describe the equations behind the Direct Plot form.   Here, Zm is described.  It plots the input impedance if all other ports are matched.

    You also may want to look at the portAdapter in rfExamples.  It is typically used with loadpull analysis.   Perhaps it could be used to match a circuit to the port.  Unfortunately, it's not at all documented.

    Best regards,

    Tawna

  • HI Vipul,
    One more thing...please feel free to contact Cadence Customer Support and submit a request (CCR) to enhance impedance matching in the GUI.
  • Hi Tawna

    Thanks for the reply.

    I am not sure but I think looking at the reflection coefficient (Zin-Zsor)/(Zin+Zsor) shoule be the best way of measuring impedance matching and could not find any such function in spectrRF sp analysis.

    I may be wrong as their might me some other approach to measure matching in spectrRF.

    Anyways I have put this query to customer support. Let's see what response they provide.

    Regards
    Vipul
  • Hi Vipul,

    Please let me know the Case number so I can track your Case internally and make sure that it gets to the correct folks who are RF experts.

    When you say Zsor, please clarify. Source impedance? And Zin - is that the impedance looking into the DUT?
    Within the industry, there are various ways of specifying these equations. And even within our tool, there are areas of ambiguity.
    It is critical to define all terms, in my experience. :-)

    Best regards,
    Tawna
  • in reply to engrvip

    Well, did you get any reply from them?

  • in reply to Satyanarayan

    Please don't reply to an old thread - this one is 2+ years old.  It's best to start a new thread.    Best regards,  Tawna

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