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# Cascade MOSFET Urgent Help Need ASAP

Discussion in 'Homework Help' started by derekjeter2, Nov 1, 2009.

1. ### derekjeter2 Thread Starter New Member

Nov 1, 2009
1
0

In the circuit below, both MOSFET's are operating in the saturation region. VTH = 1.5V and Kn = 1mA/V for both MOSFET's. RS2 = 1.5 kohm, R'S2 = 500 ohm, RD2 = 2 kohm, RL = 1 kohm, IDQ2 = 1 mA, and R1 + R2 = 50 kohm. The Q point of the first stage is located in the middle of the dc load line.

1) Design the circuit (find RS1, R1, and R2);

2) Calculate the overall voltage gain Av;

3) Sketch the dc and ac load lines of the second stage and determine the maximum undistorted output voltage swing.

****VTH could be VTN not sure maybe error in question**
When attempting to solve I assumed VTH was VTN.

DC Analysis 2nd stage
10 = VDSQ2 + IDQ2(RS2 + RS2') + IDQ2 * (RD2)
10 = VDSQ2 + (1*10^(-3) A)*(1.5*10^(3) ohm + 500 ohm) + (1*10^(-3) A)*(2*10^(3) ohm)
VDSQ2 = 6V

IDQ2 = KN2(VGSQ2 - VTN2)^(2)
(1*10^(-3) A) = (1*10^(-3) A/V)*(VGSQ2 - 1.5V)^(2)
VGSQ2 = 2.5V

VS1 = VGSQ2 + IDQ2*(RS2 + RS2')

VS1 = 4.5 V

VS1 = IDQ1*RS1

VDSAT = VGSQ2 - VTN2 = 2.5V - 1.5V = 1V
VDSQ2 > VDSAT (saturation)

IDQ1 = KN1*(VGSQ1 - VTN1)^(2)

VS2 = 10-6 = 4V

VG2 = VS2 + VGSQ2

VG2 = 6.5V

VDSQ1 = VDD/2 = 5V (due to the q point is in the middle of the dc load line)

Help on finding VGSQ1 and IDQ1?? Dont know how to find??

Last edited: Nov 1, 2009