Visjnoe
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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
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