Hello,
Here is a hard question.
IF you want to compute a Jc (Cycle Jitter) from Phase noise there are 2 ways but results are different, which is the right one and why?
the ways are:


1) Jc^2=(1/(pi*fc)^2)*∫S(f)*sin²(pif/fc)df
2) Jc =(1/(2*pi*fc)))*√(∫(S(f)df)

S(f) is the PSD of phase noise

So.... who is the one to know the answer ?
Erez

Hi,
Thanks for the answer but I don't understand.
Jc =(1/(2*pi*fc)))*√(∫(S(f)df) --> there is no Sin² , where did it go? is it only correct for White noise source to use this formula ? can you explain?
As I understand the sin² went because you can assume its 1/2 (rms of sin) intg(a*b) ~=intg(a)intg(b)=intg(a)*1/2 (where "b" is the sin²)

Thanks,
Erez

P.S can you direct me to files also ?

What I find funny about the whole jitter question is that at the end of the day the theoretical expectations tend to be totally lost in the noise (bad pun) of the environmental noise of cross coupling, power and ground rail noise and similar.

Most of the time people dont model all of the second order effects. For ring oscillators, all the second order junk tends to dominate the performance and the theoretical expctations are created from a deficient model.

GIGO - results are only as good as the model simulated.

LC VCO's tend to be closer in correlation to the model due a simpler architecture and less sources of second order problems. However, in the RF world people tend to talk "spectral spreading" for these, rather than "jitter"