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PORT with mismatch

itos

Hi,

I use a port but I have a mismatch: It's 50 ohm source resistance (as it should be) but what follows it's "undefined" (complex network including mixers etc).


I want to use the PORT for measuring the noise figure and the PSS transfer transfer function.

The noise figure works.

However, the transfer function not: If I say pac_mag=1 the amplitude at the port output would be 1V assuming perfect match. So the result is wrong. If I would know the input resistance of my circuit I could back calculate which amplitude I need to set in order to have 1Vpk at the PORT output. But this is not an option.

I also tried to divide the output by this node voltage but this does not work either - most likely because of the different frequency ranges Vout(fbb)/Vin(Vrf):

dB20(mag(value(v("/vout" ?result "pac") "harmonic" -1)/value(v("/vin" ?result "pac") "harmonic" 0)))

Any ideas?

Parents
  • Andrew Beckett

    Usually with a matched system like this you'd measure power gain, but if you want to plot the small signal voltage conversion gain from the input to the output, I'd suggest you start with the "Voltage Gain" choice on the direct plot form (for pac) - and then add this expression to the output to see what it generated. It should be something like this:

    db((harmonic(v("/vout" ?result "pac") '-1) / harmonic(drplPacVolGnExpDen("v(\"/vin\" ?result \"pac\")" '(0) nil) '-1)))

    Regards,

    Andrew.

Reply
  • Andrew Beckett

    Usually with a matched system like this you'd measure power gain, but if you want to plot the small signal voltage conversion gain from the input to the output, I'd suggest you start with the "Voltage Gain" choice on the direct plot form (for pac) - and then add this expression to the output to see what it generated. It should be something like this:

    db((harmonic(v("/vout" ?result "pac") '-1) / harmonic(drplPacVolGnExpDen("v(\"/vin\" ?result \"pac\")" '(0) nil) '-1)))

    Regards,

    Andrew.

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