Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
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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 4:04 pm
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.