fz2101
Junior Member
Offline
Posts: 17
|
In a standard LC VCO, the #1 noise contributors are the cross-coupled pair transistors. After that, it is the tail-curent transistor, and multiple papers have talked about adding a tail capacitor, or a combination of L and C to filter out the higher harmonics at that node. Along the same line, a VCO in a large IC system usually runs off an LDO instead of an "ideal" supply, and I believe that the effect of noise up-conversion from the LDO should be similar to the noise up-conversion of the tail current transistor noise, i.e. nonlinearity -> AM-to-FM conversion. I am seeing in simulation that the LDO is a significant noise contributor, but since I have not seen papers talking about this, I assume there must be some flaw in my thinking or my LDO design. Has any one seen this problem before? Note: I'm interested in very close-in phase nosie (e.g. ~1kHz offset). Thanks.
|