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Below are all of the forum threads, including all
the responses to the original posts.
Post subject: supply noise rejection for LC VCO Posted:
Mon Feb 20, 2006 8:50 pm
Joined: Mon Feb 20,
2006 8:49 pm
If the supply is the much noiser than the
ground, which biasing scheme is better for a cross-coupled LC VCO? Biasing
from bottom with NFET or from the top with PFET? Thank you.
Post subject: VCOPosted: Wed Feb 22, 2006
Joined: Wed Feb 22, 2006 3:51 pm
I suspect it depends on what junction capacitance
is being used to control the frequency, and which voltage it references.
That said, if you really can maintain a good constant current from
the supply (the PFET option), the current source will isolate the noise.
But, if you simply use a current mirror, all bets are off - you really
do need to keep constant current.