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Phase noise

I've seen this formula quoted without explanation by two different sources:

P/N(dbc)= PNF+20logN+10logFr, where PNF is technology dependent Phase Noise Floor. N is the main division rate. Fr is the reference frequency.

I don't understand the PNF+10logFr terms.

I'm familiar with adding 20logN to reference phase noise to calculate the "multiplied-up" phase noise at the VCO, assuming perfect phase detector and divider. The above seems to neglect reference noise and focuses on imperfect divider/phase detector technology.

What is PNF and why 10logFr?

TIA

Reply to
Andrew Holme
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I haven't seen it written like that, but it's reasonable for something like an app note where you don't want to go into too much depth and you aren't responsible for the outcome. ;)

PNF seems to be a fudge factor that hides most of the actual physics, like I_S in the Ebers-Moll equation.

The 10 log Fr term is the reference oscillator jitter. The RMS phase fluctuations due to additive noise (such as the noise of an oscillator with good ALC) is

= sqrt[ P_noise /(2 * P_carrier)],

and the phase noise power is proportional to the square of . The noise bandwidth of the oscillator is proportional to the centre frequency, assuming constant resonator Q, so the reference channel noise goes as 10 log F_r, at least under the above assumptions.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs
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ElectroOptical Innovations
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Reply to
Phil Hobbs

The 20*log(N) is simply the transfer function of (vout/vin) of the loop.

The other stuff is a function of vin.

Do this, write a simple transfer function for a basic loop with, Kd, Kv, Fs and 1/N, for gains of the det, vco, filter and divder.

It=92ll be clear.

Reply to
j

The 20*log(N) is simply the transfer function of (vout/vin) of the loop.

The other stuff is a function of vin.

Do this, write a simple transfer function for a basic loop with, Kd, Kv, Fs and 1/N, for the gain of det, vco,filter and div..

It=92ll be clear.

Reply to
j

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