Hi, kioas2003,
Hopefully this helps.
[quote author=kioas2003 link=1057299951/0#0 date=1057299947]Currently, I 'm doing the phase noise measurement for an integer-N frequency synthesizer (Giga Hz range).
1)Can we calculate the actual jitter at the output of the vco by measuring the jitter at the output of the divider?
1a)If there is the case, what is the relationship between them? [/quote]
How do you do the jitter measurement? Is your result in degrees or seconds? Theoretically, suppose your division ratio is N, then your results in degrees at the output of the divider should be 1/N of the result at the output of the VCO.
Quote:1b) How to convert the jitter information to phase noise infomation?
The jitter infomation is only related to the integrated phase noise information in my understanding. In other words, you can not get a spot phase noise performance, ie, how many dBc/Hz 100KHz offset from the carrier from the jitter measurement results. There is an equation:
jitter in radians = sqrt(2*integration(L(f), df, f1, f2))
L(f) is the SSB phase noise curve in dBc/Hz. f1 and f2 are the application specified frequency range.
Quote:2)Would the power of the vco output affect the phase noise measurement result if the measurement was done at the output of the vco buffer using a spectrum analyzer ?
In the designing stage, yes, the VCO output power affects the phase noise performance. We should always maximize the VCO power. In the measurement stage, no, the phase noise result will not be affected by the buffer. Neither will it be affacted by how much power is coupled to the spectrum analyzer because the carrier and noise power are reduced by the same ratio and you are measuring the relative difference (dBc).
Quote:The reason why I measuring the jitter at the output of the divider as we're having diffficulties in measuring the phase noise directly at the output of the vco due to termination problem.
I hope someone can help me on these issues.