Chapter 5

NMOS Transistor

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

Nmos regions

Region	$v_{GS}\,$	$i_{D}\,$
Cutoff	$v_{GS}<V_{to}\,$	0
Triode	$v_{DS}\leq v_{GS}-V_{to}\,$	$i_{D}\propto v_{DS}$
Saturation

• 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 $v_{GS}$