sprinkler
Newbie level 1
lo phase noise
When we talk about the VCO or PLL phase noise, we rarely specify explicitly it's the PM or AM noise. And simulation and measurement always give the total of the both.
However, when LO is used to perform frequency translation with RF via a mixer, it is not a straightforward multiplication (which is exactly what we've assumed in the analysis).
In the context of a Gilbert mixer, LO just commutates the switches sharply during its cross-zero points, making PM noise on LO directly get into the IF. Once that's done and one switch is on and the other off, AM noise on LO hardly finds its way into mixer (somewhat like cascode noise).
Maybe there is some other AM-PM mechanism (if there is, can anybody tell me?). But at least, can we say that AM PN is greatly suppressed during the hard switching?
Do we truly overestimate system degradation (SNR, ACS) introduced by the measured phase noise?
When we talk about the VCO or PLL phase noise, we rarely specify explicitly it's the PM or AM noise. And simulation and measurement always give the total of the both.
However, when LO is used to perform frequency translation with RF via a mixer, it is not a straightforward multiplication (which is exactly what we've assumed in the analysis).
In the context of a Gilbert mixer, LO just commutates the switches sharply during its cross-zero points, making PM noise on LO directly get into the IF. Once that's done and one switch is on and the other off, AM noise on LO hardly finds its way into mixer (somewhat like cascode noise).
Maybe there is some other AM-PM mechanism (if there is, can anybody tell me?). But at least, can we say that AM PN is greatly suppressed during the hard switching?
Do we truly overestimate system degradation (SNR, ACS) introduced by the measured phase noise?
