Community RF Design HB: duplicated frequencies in 3-tone simulation

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HB: duplicated frequencies in 3-tone simulation

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I get multiple results at the same frequency in a 3-tone simulation.

I try to determine the IP3 of a mixer. I have 3 large signal tones: 0.75 GHz, 1.25 GHz and 1.26 GHz.

At the IM3 frequency of 490 MHz I observe 4 results, see also the screenshot of the table output. The frequencies are exactly the same (even when I subtract 490 MHz by using xval() ).

Which of the values do I have to use to determine the correct IP3?

Is there an option to merge these results?

  • This will be because your frequencies are commensurate (they have some fairly big common factors) so you are almost certainly ending up with different harmonic combinations ending up at the same frequency. For example, if I simulate with 10 harmonics of each tone, I can find the harmonic combinations:

    setof(freq harmonicFreqList(?result 'hb_mt_fi) nearlyEqual(cadr(freq) 490.0e6))
    (((-6 5 -1) 4.9e+08)
    ((-1 2 -1) 4.9e+08)
    ((4 -1 -1) 4.9e+08)
    ((9 -4 -1) 4.9e+08)
    )

    You typically would want to use a measurement which uses the "fi" results - see What is the difference between the qpss-fi and qpss-fd results? - either using th "fi" results and the harmonic() function, or the vh() function. It's almost certainly the second combination in my list above that you want - that would likely be the IP3 result (I assume that the 0.75G is the LO, and the other two are the close tones - if so, the (-1 2 -1) combo is an IP3 (|2|+|-1| is 3).

    Andrew

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