Ele591I E-Testing II
Final Exam

Figure 2

2. Consider the circuit shown in Figure 2.

   The identical transistors have a threshold voltage of 1V
   and (W/L)uCox/2 = 10^-4 amp/Volt²

   1. What is the output current, Io?

   2. What does the output voltage, Vo, have to be to keep M2 in saturation?

Answer

Equate current through the resistor to M1 drain current,

(5-Vgs)/5K = 10^-4[Vgs-1]²

5-Vgs = 0.5[Vgs²-2Vgs +1]

Vgs² = 9

Vgs = 3V

Io = Id = (5-Vgs)/5K = 400 uA

For M2 to remain in saturation

Vo = Vds > Vgs - Vtr = 3-1 = 2V

Vo should be greater than 2 Volts