Amplitude noise to phase noise conversion carried out by the varactor in VCO is one of the phase noise sources. What I can not understand is:
the am noise modulating the varactor has to be low frequency to be converted to PM around the carrier, however the low frequncy am noise is attenuated by the LC tank and thus should be small, while the am noise at frequency around the carrier can only be converted to pn noise far away from the carrier. Then there should be very tiny amount of am noise converted to PM around the carrier, which is opposite to my simulation and experience.
What I have misunderstood? Please help me out.