supply noise rejection for LC VCO

[boshiouke]

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.

 

[vfone]

Noise is multiplied by gm of the active device. Probably in your case would be better to choose a bias from bottom.

 

[rfsystem]

A short hint: Trust your simulator!

Please simulate the AM->FM conversion from VDD, VSS ans Substrate. Apply a sinewave source on these supplies and observe the sideband spurs. The conversion effects are difficult to understand and depend on circuit topology and nonlinearity of the capacitive components.

The netlist and the result give you the best knife to learn and built!