Small signal model of Metal oxide semiconductor FET

small signal model of MOSFET

1. Cut-off Region In the case the transistor is in the cutoff region, ID = 0 which results the following small signal model In the cutoff region, the transistor is essentially an open circuit for all the nodes.

2. Triode Region If the transistor is in the triode region, the small signal model is to have a fixed resistor, rds , between the drain/source nodes as shown below .

3. Active Region For the active region, the small signal model is to have a voltage-controlled current-source between the drain and source as well as a resistor, ro that models the increase in the drain current as the drain/source voltage increases.