For inverter circuit with depletion type nMOS load, the gate and the source nodes of the load transistor are connected, hence Vgs(load) = 0 always? why is 0 ? anyone can explain it?
In a depletion-mode nMOS the channel area is doped so that the channel exists even with no (positive) applied Vgs. Thus, the threshold of a depletion-mode is typically negative. The short-circuit between Gate and Source (i.e. Vgs=0) ensures that the transistor is always on since:
VT<0,Vgs=0
-VT>0,Vgs=0
Vgs-VT>0