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Measurements >> RF Measurements >> phase noise measurement
https://designers-guide.org/forum/YaBB.pl?num=1183282925

Message started by chenyan on Jul 1^st, 2007, 2:42am

Title: phase noise measurement
Post by chenyan on Jul 1^st, 2007, 2:42am

What is the difference of phase noise measured using spectrum analyzer and signal source analyzer? Is there any reference discuss this topic? Thanks

Title: Re: phase noise measurement
Post by didac on Jul 1^st, 2007, 7:43am

Hi,
I will share my limited experience in phase noise measurements
1)With a spectrum analyzer you usually have a software module embedded to perform the phase noise analysis, this analysis it's as is;I mean the spectrum analyzer will give you a dirty measurement because he won't detect parasitic AM/FM modulations.
2)A signal source analyzer is an instrument specially designed for this kind of measurements, you can do a closed-loop with it and your oscillator(will act as a PLL and the control voltage will be generated directly by the instruments ensuring a little frequency drift), also it will be capable of minimize parasitic modulations(I think they use a correlation method to detect them an eliminate them from the measurement) so the measurement will be more "clean",stable and repetitive.
Hope it helps,

Title: Re: phase noise measurement
Post by chenyan on Jul 2^nd, 2007, 1:27am

Thanks a lot, didac.

I still have some questions unclear

(1), the ssa performs a close-loop measurement, then wont the loop filter affect the phase noise measurement?

(2), the parasitic AM/FM, what exactly do you mean? Could you please give more explainations.

Thank you.

Title: Re: phase noise measurement
Post by didac on Jul 2^nd, 2007, 2:04am

Hi,
You are right the loop filter affects the measurement, playing with the value will give you slightly different measurements of phase noise, but I think that if you follow the users guide of the ssa the amount of error will be small enough to not be noticeable.
Regarding the parasitic AM/FM modulations, in a VCO noise coupled to the VDD modulates the output waveform of the circuit in AM manner while noise coupled to the VCONTROL of the VCO will transform to the frequency domain like an FM modulation, this issues can cause a bad phase noise performance. It highly depends on the setup of your measure(number of wires,use of shielded wires,type of probes,external decoupling capacitors,on-chip capacitors,layout isolation techniques...)this effect will be more or less annoying.
Hope it helps,

Title: Re: phase noise measurement
Post by chenyan on Jul 4^th, 2007, 12:58am

thanks, didac