What harm does it do if psub is floating?

[cnc7]

Hi
If Ptap is not connected to psub(ground)? What harm does it
do if psub is floating?

thx

 

[varunmjman]

Floating psub

Your substrate is always prone to noise. Its also necessary to bias the substrate to avoid latchup problems...
So it is essential to connect the substrate to the lowest potential...
Plus the threshold voltages of MOS depends on the biassing of the substrate... So if you dont connect the Psub to a commonn potential then all the NMOS, which are built on the P substrate, will have differenent and unpredictable threshold voltages..
So its essential that you bias the substrate..