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Determining the frequency of oscillation using the calculator function

wgtkan

Hello,

There are a number of ways to determine the frequency of oscillation for an Oscillator. 1) Using the linear stability analysis, 2) using periodic stability analysis. In these two cases, a stability probe has to be used. 

Will a calculator function called frequency, computes the frequency of oscillation from the transient response?

Thanks a lot.

  • The standard stability analysis is going to look at the stability assuming a static (not time varying operating point) and usually (unless the oscillator is very linear) will not give the correct frequency. You can use periodic stability, but this will have found the frequency anyway via the pss analysis, so it's mainly useful to understand how stable the oscillation is - the harmonic frequency of the PSS will have told you the oscillation frequency (that's probably going to be your best bet).

    The frequency function will tel you the average frequency of a transient waveform - so you'd want to leave it to settle, and then clip out a few cycles and use frequency. Or you could use freq() to get the instaneous frequency versus time.

    I'd use PSS though - this solves for the oscillation frequency and you can directly get the frequency of oscillation (use the direct plot form to get this, and you can send the result to the outputs to add a measurement).

    Andrew.

  • in reply to Andrew Beckett

    Hello Andrew,

    So in PSS simulation result > direct plot > main form and harmonic frequency and then the fundamental. fosc = (fmax + fmin)/(2). 

    Thanks a lot.

  • in reply to wgtkan

    What's fmax or fmin? There's no fmax or fmin on the direct plot form (I don't know what it would mean anyway). The direct plot form allows you to get the expression for a specific harmonic (probably the first) and this will give the frequency directly.

    Andrew.

  • in reply to Andrew Beckett

    Hello Andrew,

    The fmax is the maximum frequency and the fmin is the minimum frequency.  I am attaching the following image. In this case the fmax = 2.615GHz and the fmin = 2.536GHz

    Thanks a lot.

  • in reply to wgtkan

    Presumably you're sweeping something, in which case the plot of harmonic 1 would give the frequency versus the swept variable. Not sure how meaningful it would be to take the average - it rather depends on what your varying...

    For a single simulation you only see one frequency.

    Andrew.

  • in reply to Andrew Beckett

    I am sweeping the tuning voltage which I defined as a variable over voltage.  
    So if I don’t sweep the Voltage, I will get a single oscillation frequency through PSS?

    Thanks a lot.

  • in reply to wgtkan
    wgtkan said:
    So if I don’t sweep the Voltage, I will get a single oscillation frequency through PSS?

    Yes, that's what I said. Not sure why you'd expect to get more than one frequency if you didn't sweep anything...

    Andrew.

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