MOSFET Operating Regions

1. Cutoff Region

Condition:

V_GS < V_T

Drain Current:

I_D ≈ 0

Concept:

MOSFET is OFF. No current flows.

2. Linear (Ohmic) Region

Condition:

V_DS < (V_GS - V_T)

Drain Current Equation:

I_D = k [(V_GS - V_T)V_DS - V_DS²/2]

Concept:

Acts like a voltage-controlled resistor.

3. Saturation Region

Condition:

V_DS ≥ (V_GS - V_T)

Drain Current Equation:

I_D = (1/2) k (V_GS - V_T)²

With Channel Length Modulation:

I_D = (1/2) k (V_GS - V_T)² (1 + λV_DS)

Concept:

Acts like a current source. Current mainly depends on V_GS.