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PSS, PNOISE and other simulations for a circuit containing an oscillator and Mixer

Tiago Silva

Hello

I am simulating a Mixer circuit with a cross-coupled oscillator, but I am not sure how to perform PSS, PNOISE and other harmonic balance analysis without the LO port for the mixer.

When analyzing the PSS, I used the oscillator option and pointed to the oscillator outputs. The PSS converged, but the RF input source is being ignored in PNOISE and NF is disabled.

Is it possible to fix this problem? Is this the correct way to measure?

Parents

  • I'm slightly surprised that I didn't find any report of this restriction. I think that if you have an oscillator driving the LO on a mixer, and have the input signal for the mixer being a port (without any time-varying signal), then you should be able to compute noise figure - it's just that the pnoise and hbnoise forms assume you can't so don't give you the option to specify the input port or reference side band.

    You can make this work though:

    1. Set the sweep to absolute or use relative with 0 as the Relative Harmonic and then sweep the output frequency (the base band signal assuming this is a receiver mixer)
    2. Set the noise time to time average and pick USB
    3. On the Options form, in the additionalParams at the end, enter:
      for pnoise: iprobe=PORT0 refsideband=-1
      for hbnoise: iprobe=PORT0 refsideband=[-1]
      where PORT0 is the name of your input port. The -1 is assuming that the correct input signal is at the lower sideband of the LO - use 1 if it's from the upper sideband.

    Then on the direct plot form you should be able to plot the Noise Figure (I only quickly tried this and not with a mixer with an oscillator attached - I'm travelling this week so didn't have time to test).

    Probably worth reporting this to customer support as I think the analysis form should allow this to be done directly without the trickery above. A sensible enhancement as far as I can see...

    Andrew

Reply

  • I'm slightly surprised that I didn't find any report of this restriction. I think that if you have an oscillator driving the LO on a mixer, and have the input signal for the mixer being a port (without any time-varying signal), then you should be able to compute noise figure - it's just that the pnoise and hbnoise forms assume you can't so don't give you the option to specify the input port or reference side band.

    You can make this work though:

    1. Set the sweep to absolute or use relative with 0 as the Relative Harmonic and then sweep the output frequency (the base band signal assuming this is a receiver mixer)
    2. Set the noise time to time average and pick USB
    3. On the Options form, in the additionalParams at the end, enter:
      for pnoise: iprobe=PORT0 refsideband=-1
      for hbnoise: iprobe=PORT0 refsideband=[-1]
      where PORT0 is the name of your input port. The -1 is assuming that the correct input signal is at the lower sideband of the LO - use 1 if it's from the upper sideband.

    Then on the direct plot form you should be able to plot the Noise Figure (I only quickly tried this and not with a mixer with an oscillator attached - I'm travelling this week so didn't have time to test).

    Probably worth reporting this to customer support as I think the analysis form should allow this to be done directly without the trickery above. A sensible enhancement as far as I can see...

    Andrew

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