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Design >> RF Design >> supply noise rejection for LC VCO
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Message started by boshiouke on Feb 20^th, 2006, 11:00am

Title: supply noise rejection for LC VCO
Post by boshiouke on Feb 20^th, 2006, 11:00am

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.

Title: Re: supply noise rejection for LC VCO
Post by Visjnoe on Apr 17^th, 2006, 3:21am

Hi,

if the supply is noisier than the ground, I think your better of with a PMOS (biasing) current source on top of the
cross-coupled pair. You can understand this by considering the 'limit' case where the PMOS current source acts as an ideal (SPICE) current source:
not disturbances coming from the supply can now enter your tank anymore!

Make sure to keep in mind the noise/PSRR of your VCO control voltage too!

Kind Regards

Peter