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pnoise spurs at multiples of clock frequency.

vamshiky

Hi,

 I have a simple inverter driven by a square wave, and ran pnoise on the circuit.

There is flicker and thermal noise and after that  has huge spurs ( about +20dBc ) at 2*Ffref , 5*Fref.

And this goes away if I carefully choose the sweep type and step size (delberately avoiding those freq points during sim). 

 

Also I have noticed from earlier posts that while running pnoise sim, simulator automatically skips the freq point which is exact multiple of beat frequency and gives a message "Infinite flicker noise is ignored"

however I dont see this happening in my sims.

Are there any additonal settings/options which I missed out.

 

Thanks,

Vamshi 

 

Parents

  • OK, then I am only left with carefully choosing the step sizes/ sweep points. Linear step size with an irrational number does the job but actually slows my sims on actual circuit chargepump for PLL. (ofcourse still see a bit of wierd behaviour at high frequencies)

    Do you have any better suggestions to avoid those near/exact multiple frequencies in sims.

    Thanks,

    Vamshi

Reply

  • OK, then I am only left with carefully choosing the step sizes/ sweep points. Linear step size with an irrational number does the job but actually slows my sims on actual circuit chargepump for PLL. (ofcourse still see a bit of wierd behaviour at high frequencies)

    Do you have any better suggestions to avoid those near/exact multiple frequencies in sims.

    Thanks,

    Vamshi

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