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Design >> RF Design >> A basic Question Regarding impact of spurs on jitter
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Message started by raja.cedt on Dec 27^th, 2011, 2:24am

Title: A basic Question Regarding impact of spurs on jitter
Post by raja.cedt on Dec 27^th, 2011, 2:24am

hello every one,
I have a basic Question regarding impact of spur on integrated rms jitter. When we multiply every individual block phase noise with respective transfer function and add all we get total pll phase noise curve, but we don't get spurs in this process but in the real time we get spurs at the reference frequency and those spurs add some thing to area, so while modeling how to consider this impact?

Thanks,
Raj.

Title: Re: A basic Question Regarding impact of spurs on jitter
Post by loose-electron on Dec 28^th, 2011, 10:45am

Depends on what is in your model I would think.

One comment first: Jitter or Phase noise? Two different ways of looking at the same thing.

You need to model your feedthrough
and feedback paths with more detail in order to
see the second order effects that you are talking about.

What you seem to be describing is a simple hand analysis?

Title: Re: A basic Question Regarding impact of spurs on jitter
Post by raja.cedt on Dec 28^th, 2011, 11:15am

hello loose electron,
thanks for your responce. I know that jitter and phase noise are related. Could you please tell me how to model reference spurs in the model? I would like to incase of a simple 2nd order loop filter pll.

Thanks,
raj.

Title: Re: A basic Question Regarding impact of spurs on jitter
Post by loose-electron on Dec 29^th, 2011, 2:19pm

transistor level model or behavioral?

If its at the transistor level, I would get rid of everything except phase detector, charge pump and filter.

(faster to simulate)

set up a simulation where you do an FFT of the VCO control voltage (Filter output)
with everything else behavioral.

Title: Re: A basic Question Regarding impact of spurs on jitter
Post by raja.cedt on Dec 30^th, 2011, 7:06am

hello loose-electron,
what is the use of estimating Control voltage FFT? i know it gives more or less phase noise scaled by Kvco am i correct?

Any how thanks i will try implement this.

Thanks,
raj.

Title: Re: A basic Question Regarding impact of spurs on jitter
Post by loose-electron on Dec 30^th, 2011, 3:37pm

You were looking for spurs due to the reference frequency feeding through to the VCO output.

What I just described should look at that effect and just that effect.

Thus the suggestion.