Question 17. In the circuit shown below, VDD is 9 V. The resistor values are RD = 3.3 KΩ, RS = 2.2KΩ, and RG = 470 KΩ.
Find the voltage at the gate of the MOSFET.
Find VDS (in V) if ID = 1 mA.
Find ID (in mA) when the MOSFET parameters are k’(W/L) = 1 mA/V and Vt =1.2 V.

Answer 17.

Since the current entering the gate of a MOSFET is 0, then the valtage at the gate of the MOSFET is 0 V.

2V_DD = V_RD + V_DS + V_RS
2*9 = 3.3*1 + V_DS + 2.2*1
V_DS = 12.5 V.

I_D=0.5* k’_n(W/L)*(V_GS - V_t)², since V_GS = V_G – V_S = 0 – (R_sI_D – V_DD)  =V_DD -2.2*I_D
I_D=0.5* 1*( 9-2.2*I_D – 1.2)²
Solve to get I_D = 2.52 mA.