Problem 5.9

An NMOS transistor with a k_n = 1 mA/V² and V_t = 1V is operated with V_GS = 2.5 V. At what value of V_DS does the transistor enter the saturation region? What value of I_D is obtained in saturation?

As you can see from the graph from page 249 the transistor enters the saturation region when the V_OV = V_DS.

V_OV = V_GS - V_t

V_OV = 2.5 V - 1 V

V_OV = 1.5 V

V_DS = 1.5 V

To find I_D we use the formula:

I_D = 1/2 k_N(V_OV)²

I_D = 1/2 (1 mA/V²)(1.5V)²

I_D = 1.125 mA