what is substrate noise
A MOS device is in fact a 4 terminal device. The 4th terminal is the substrate.
The bulk-source potential modulates the drain current with a transconductance of gmb which has the same polarity as gm
(i.e., increasing the bulk potential increases the drain current) The substrate has a finite (nonzero) resistance and therefore has thermal noise.
How to reduce put as many contacts as possible
Reduces possibility of latch up issues
Lowers Rsub and its associated noise(Impacts LNA through backgate effect (gmb)
Absorbs stray electrons from other circuits that will otherwise inject noise into the LNA
Cons: takes up a bit extra area