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Phase noise of frequency multiplier

MTP3

Hi!

I am trying to simulate a frequency multiplier. The oscillators are simple ring oscillators oscillating at 2GHz made form inverters.What the multiplier circuit is that it cancels the fundamental tone and retains/preservs the 3rd harmonic(3,6,9...) and cancels the other harmoics like 1,2,4,5.......  

The problem;

I am interested in looking at the Phase noise at the combiner output oscillating at 6GHz. The output signal has a voltage swing of around 900mV. The setup does not have any ideal blocks in it. In the PSS options form I donot check the oscillator option (I read a post suggesting this in case of a driven circuit, which I assume this multiplier to be)

When I run pss using shooting method it does not converge. I have tried changing the tstab (increasing it), changing the method from trap to gear2 etc. But I can't get the pss to converge.

When I run PSS using the HB method the pss does converge but the Phase noise at the comes out to +150dbc/Hz which is a unrealistically large value  (opposed to the theroratical results).

Running a pss+pnoise for a single ring oscillator works fine. I would be grateful if someone could guide me what could be the problem or if this is the right way of simulating this kind of circuit,

Regards,

MTP 

I cannot post the image so here is a link to the circuit diagram

www.dropbox.com/.../FrequencyMultiplier.jpg

Parents

  •  Hi MTP3,

     

    Thank you for your detailed update!

    [1] - Great - this a good thing!

    [2] - I've never needed to use anything less than a maxstep of 1/100 of the period of interest for stiff oscillators in pss in the MHz range. Hence, I suspect with your 2 GHz design a maxstep value of 1/100 is more than sufficient. Perhaps you might look at the step size being used in the pss transient analysis to determine how close to the minimum steps are to 1/100 of the the 2 GHz period.

     

    [3] - Sounds good - this might provide some insight (hopefully!)

     

    Shawn

Reply

  •  Hi MTP3,

     

    Thank you for your detailed update!

    [1] - Great - this a good thing!

    [2] - I've never needed to use anything less than a maxstep of 1/100 of the period of interest for stiff oscillators in pss in the MHz range. Hence, I suspect with your 2 GHz design a maxstep value of 1/100 is more than sufficient. Perhaps you might look at the step size being used in the pss transient analysis to determine how close to the minimum steps are to 1/100 of the the 2 GHz period.

     

    [3] - Sounds good - this might provide some insight (hopefully!)

     

    Shawn

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