Chapter 5

NMOS Transistor

• N-channel enhancement-mode MOSFET (metal-oxide semiconductor field effect transistor)

Nmos regions

Region		$i_D$
Cutoff	$v_{GS}<V_{to}$	0
Triode	$v_{DS}\le v_{GS}-V_{to}$	$i_D\propto v_{DS}$
Saturation	$v_{DS}\ge v_{GS}-V_{to}$

• The threshold voltage, $V_{to}$, is the minimum $V_{GS}$ needed to move the transistor from the Cutoff to Triode region. When is reached, a channel forms beneath the gate, allowing current to flow.

• $V_{to}$ is usually on the order of a couple of volts

• For small values of $V_{DS}$, $i_D$ is proportional to $V_{DS}$. The device behaves as a resistor whose value depends on $v_{GS}$