[time-nuts] tutorial on phase noise and PLLs?

Magnus Danielson magnus at rubidium.dyndns.org
Thu Dec 4 17:59:10 EST 2014


On 12/04/2014 08:41 PM, Jim Lux wrote:
> I'm looking for a real short (3-4 slides or a website, really)
> description of why the phase noise of a PLL (microwave) looks the way it
> does, explaining (in sort of qualitative terms) how the phase noise
> transitions from the VCO (outside the loop bandwidth) to the reference
> (inside the loop bandwidth)..
> And in particular, what the phase noise curve looks like if the loop
> bandwidth is chosen incorrectly, or if the VCO or reference has more or
> less noise than expected.
> I figured before I wrote one up, if someone knows of one that's already
> out there, I could just point people to it.

I could not find any useful presentation out of Enrico's large 
collection, but he and Ulrich is my usual suspects.
But then, the best presentation I've seen was at the NIST seminar.

Anyway, this TI paper gives you a good hint:

See how Fig 8 and Fig 9 provides two different cross-overs between the 
noise responces, and how the higher bandwidth doesn't have a "hump" just 
because the steered oscillators noise response get's sufficiently 
high-passed by the loop PLL as for the lower PLL it humps up because of 
them having comparable power (amplitudes yes, but their power adds, as 
it is noice).

Maybe it is good enough for your purposes, but yes, I agree there should 
be a better presentation about the problem.


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