How to extract phase noise curve from spectrum analyzer
In measuring clock signal phase noise, we can use spectrum analyzer.
The output curve can be processed to get phase noise curve. However, the spectrum will be coved by the noise floor in large offset frequency.
How we extract the real phase noise from the output of spectrum analyzer?
There are a number of ways to do it. A simple way is to use a filter/amplifier combination.
Assume you have a 1 GHz clock. Basically, I would build a narrow band notch filter to notch out the power by say 20 dB at 1 GHz, but to be done notching out at +/- 100 KHz from 1 GHz. Then I would pass the notched signal thru a 20 dB gain amplifier and view it on the S/A. The noise floor further than 100 KHz from the carrier is now 20 dB higher.
Just be careful so that the filter or source does not drift in frequency, or you might damage the S/A front end with too much power.
If it is a digital clock, I would also lowpass filter the harmonics before hitting the S/A.
http://www.speakeasy.org/~jmiles1/ke5fx/gpib/pn.htm
what if there is no more resource?
A notch filter is a must. Probably you don't need amp after the notch.