Three working states of MOS transistor

Three working states of MOS transistor

Method for determining work area (NMOS):

When Vgs<Vth, the cutoff zone.

When Vgs>Vth and Vds<Vgs - Vth, the variable resistance region.

When Vgs>Vth and Vds>Vgs - Vth, the saturation zone (constant current zone).

Among them, Vth is an important parameter of MOS transistor - turning on voltage.

When the MOS transistor operates in the variable resistance region, its channel is "unobstructed", equivalent to a conductor. When Vds Vds<Vgs - Vth, the linear relationship of V-I is approximately satisfied, that is, there is an approximately fixed resistance value. This resistance value is controlled by Vgs, hence it is called the variable resistance region.

MOS transistor operates in a saturation region (constant current region), which is different from the saturation region of BJT. This region is called the saturation region of MOS transistor, mainly indicating that Vds increases with Id but almost no longer increases - that is, current saturation. In fact, within this saturation zone, both MOS transistor and BJT are in a controlled constant current state, so it is also known as the constant current zone.