At what kind of offsets from the carrier should the phase noise profile be measured, to give meaningful jitter characteristic ?
At least for measuring phase noise for oscillators for RF applications (especially first LO), it is very hard to get meaningfully readings within +/-1 kHz from carrier, even with high quality test equipment, unless you use some deep crystal notch filters at the carrier frequency.
Well, this begs the question: How do you do it?
Jeroen Belleman
I have a cool Windows program that converts a phase noise profile to RMS jitter. Someone in SED supplied it (maybe you? I can't remember). The author isn't identified; it's PhaseNoiseCalc v 1.01 copyright ibrt 2003.
Dear Sir:-
I must object in the strongest terms to the above use of "begs the question".
Quite. Point taken. It prompts the question.
Jeroen Belleman
Or begs (for) the question, which is a common use.
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The concept is pretty straight forward; take the single sided spectral noise power and convert it total rms jitter. Where?s it used, think about it for a second; What is one of the primary concerns when you apply a clk to any high performance digitizer?
What?s on the back end of any modern day acquisition system?
That's not an answer! You'll have to come up with something a little more explicit!
Jeroen Belleman
If the carrier-to-noise ratio is dominated by phase noise, the RMS phase jitter in radians is equal to 1/sqrt(CNR). You can derive that from the formula for sin(a+b), with a=omega*t and b a random variable.
For additive noise, it's 1/sqrt(2*CNR), because half of that noise power goes into AM (I) rather than PM (Q).
Cheers
Phil Hobbs
RMS jitter has to be specified over some observation interval. The frequency-domain phase noise spectrum gets mapped into the jitter-vs-time curve.
A cheap XO may have a picosecond of RMS jitter measured over single periods, and
100 ns RMS jitter measured over a full second. How much that matters in an ADC clock depends on what the digitized signal means.Have something to add? Share your thoughts — no account required.
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