Question

For a PMOS transistor kₚ = 80μA/Vₗ and Vₜₚ =-1.5 V. The gate is tied to ground and Vₛ = 5V . Determine the mode of operation (triode or saturation) and calculate the drain current ID for VD = 4 Volts and VD = 1.5 Volts (For VD = 4V, ID = 240μA for VD = 1.5V ID = 490μA ) (Note that when VD = 1.5V the transistor is right on the line between the triode and saturation regions, so either equation for ID will give you the same value of ID)

Answer 1

The PMOS transistor operates in saturation mode for VD = 4V with a drain current of 240μA. At VD = 1.5V, it's on the edge between triode and saturation with a drain current of 490μA.

Step-by-step explanation:

For a PMOS transistor with k₊ = 80μA/V² and Vₜₚ =-1.5 V, when the gate (VG) is tied to ground (0V) and VS = 5V, we proceed to determine the mode of operation and calculate the drain current ID.

To find the mode of operation, we must compare VD with VSD - |Vₜₚ|:

For VD = 4V, VSD = VS - VD = 5V - 4V = 1V. Since 1V < |Vₜₚ| (1.5V), the transistor is in saturation.

For VD = 1.5V, VSD = VS - VD = 5V - 1.5V = 3.5V. Since 3.5V is equal to |Vₜₚ|, the transistor is at the edge of triode and saturation.

Using the saturation current equation (given that the transistor is in saturation when VD = 4V):

ID = 0.5 x k₊ x (VSG - |Vₜₚ|)² = 0.5 x 80μA/V² x (5V - 1.5V)² = 240μA

For VD = 1.5V, as the transistor is at the edge, either triode or saturation equations would give:

ID = 490μA (as specified in the question).