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supply noise rejection for LC VCO - RF Cafe Forums

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 you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


boshiouke
Post subject: supply noise rejection for LC VCO Posted: Mon Feb 20, 2006 8:50 pm

Lieutenant

Joined: Mon Feb 20, 2006 8:49 pm
Posts: 1
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.


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fred47
Post subject: VCOPosted: Wed Feb 22, 2006 4:04 pm

General


Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104
Hi,
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.

Good Luck!



Posted  11/12/2012
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