Hi Ken,
Thanks very much for your response, that really helps me a lot.
Assumed that thermal noise generates AM and PM noise in a VCO system as a(t) and phi(t):
Quote:V(t) = (1 + a(t)) * cos(2*pi*fc*t + phi(t))
=(1 + a(t)) * [cos(2*pi*fc*t) * cos(phi(t)) - sin(2*pi*fc*t) * sin(phi(t))]
If sin(phi(t)) is very small (much smaller than 1),
then V(t) ~ (1 + a(t)) * [phi(t) * sin(2*pi*fc*t)]
To be more clear, phi(t) should be at one specified large offset frequency fm, which is phi(t) * cos (2*pi*f
mt). Besides, all PM noise phi(t) transfer to voltage (power) domain and value is:
Quote:|V(t)| = |1+a(t)| * |phi(t)|
However, if all PM noise use this way transfering to power domain noise S
V, S
phi and the PM component of S
V should be the same. Actually, if I assume there are three kinds of noise in nature: AM+PM noise, pure PM noise, and pure AM noise. AM+PM noise (for example: thermal noise) should contribute same PM noise in S
phi and S
V. In S
V, PM noise transfer to power domain using above formula. On the other hand, if we have a pure PM noise, it couldn't generate power and transfered its PM noise to power domain.
My opinion is all PM noise (not only AM+PM noise but PM noise) contribute to S
phi, and only PM components of AM+PM noise contributes to S
V, pure PM noise couldn't. So S
phi and the PM component of S
V are not the same. Is this correct?
Sincerely yours,
Daniel