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Unrealsitic Fmax simulation of IBM 90nm in cadence

niranjan1984

Hello All,
  I am trying to measure Fmax of IBM 90nm technology in cadence. I am measuring S parameters and plotting Gumx. I get Fmax around 500GHz for 90nm while reported Fmax for 90nm are around 300GHz. I am using rfmos transistor & technology uses BSIM4.4 model. I am not sure what I am doing wrong please help.

Thanks

  • Probably best to contact IBM, since it's their model.

    Andrew

  • Thanks Andrew. Just want to make sure that if Gumx in spectre is the Masons Unilateral Gain (U) ? Please clarify, I read few contradicting posts

    1. Fmax simulation in cadence /blogs/rf/archive/2011/08/11/measuring-fmax-for-mos-transistors.aspx tells you have to plot Gumx to get Fmax

    2. Few posts say Gumx is not U http://www.designers-guide.org/Forum/YaBB.pl?num=1272508752/1,http://www.edaboard.com/thread167090.html

    Please clarify

     

    Thanks

  • Search in cdnshelp for Gumx - you'll see the equation. I'm not really familiar with "Mason's Unilateral Gain"- maybe Tawna will chime in - but the documentation does describe the equation in terms of the s parameters.

    Andrew.

  • Hopefully the screenshot below will show up.   

    Here is equation 8.3 of Mason Unilateral Gain from Vendelin, Pavio, and Rohde’s book

    Microwave Circuit Design Using Linear And Nonlinear Techniques.  

    We don’t calculate U.   You could come up with a calculator expression for this.

    The closest we calculate is Gumx.

    Chapter 10 of the MMSIM11.1 Virtuoso® Spectre® Circuit Simulator and Accelerated Parallel Simulator RF Analysis User Guide

    contains the different gains that we calculate and their equations.

    GA (available gain) is the power gain obtained by optimally matching the output of the network.

    GP (power gain) is the power gain obtained by optimally matching the input of the network.

    GT (transducer gain) shows the insertion effect of a two-port circuit. This quantity is used in amplifier design.

    Gumx (maximum unilateral transducer power gain)

    Gmax (maximum available gain) shows the transducer power gain when there exists a simultaneous conjugate match at both ports.

    Gmsg (maximum stable gain) shows the gain that can be achieved by resistively loading the two-port such that k = 1 and then simultaneously conjugately matching the input and output ports. For conditionally stable two-ports, you can approach the maximum stable gain as you reduce the input and output mismatch. If you attempt a simultaneous conjugate match and k < 1, the two-port oscillates.

    Best regards,

    Tawna

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