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How to read exactly the value of impedance from the plotting of Gmin vs frequency?

anhnha

 Hi.

I am plotting Gmin ( optimum noise reflection coefficient) of a LNA in Smith chart.
I swept Gmin versus frequency (for example, ranging from 1GHz to 3GHz).

Is there a way to read out optimum noise impedance at my interested frequency, say 2GHz, from the curve?
I know that I can point the cursor over the curve, find the interested frequency and then read out the impedance. However, that method is not exactly at all.

How to read exactly the value of impedance from the plotting of Gmin vs frequency?

  • Plot the Gmin from the direct plot form and then do Right Mouse->Send to Calculator. This should be this expression:

    gmin(getData("Gopt" ?result "sp_noise") getData("Bopt" ?result "sp_noise") zref(1 ?result "sp"))

    You can then use the value() function in the calculator to find the value at 2G. This will be a complex number - so you might want to take the real() or imag() of it. For example:

    value(gmin(getData("Gopt" ?result "sp_noise") getData("Bopt" ?result "sp_noise") zref(1 ?result "sp")) 2G)

    or:

    imag(value(gmin(getData("Gopt" ?result "sp_noise") getData("Bopt" ?result "sp_noise") zref(1 ?result "sp")) 2G))

    Also, in the graph (assuming you're using IC615 or later) you can turn on the snapping cursor (on the Marker menu) which would make it easier to get the value as you move along the curve - because it would then snap to the simulated points, rather than interpolating between them.

    Kind Regards,

    Andrew.

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