- #1

francisg3

- 32

- 0

A Common-Source amplifier utilizes a MOSFET with µnCox = 400µA/V2, W/L = 10, and VA = 10V. It is biased at ID = 0.2 mA and uses RD = 6 kΩ. Find Rin, Avo and Ro. Also, if a load resistance of 10kΩ is connected to the output, what overall voltage gain Gv is realized? Now, what if a 0.2V peak sine-wave signal is required at the output, what must the peak amplitude of vsig be?

Below I have included the general model of the MOSFET along with what I believe is the equivalent pi-model.

I have found Ro to be RD//ro = (50*6)/(56) = 5.35kΩ (that part is correct according to the answer key.

where ro= VA/ID = 10/0.2 = 50kΩ

What I am having trouble with is the Avo and Gv.

I have the following:

ID = 0.5*Kn*(W/L)*(Vov^2)

subsituting values I get:

200 = 0.5*(400)*(10)*Vov^2

therefore Vov = 0.3162 Volts

gm = Kn*Vov

=(0.4)*(10)*(0.3162)

therefore Avo = -gm*(RD//ro)

= -(0.3162)*(5.3535kΩ)

= -6.76 (the answer is -2.14 V/V

Where did I go wrong? Any help would be appreciated!

Below I have included the general model of the MOSFET along with what I believe is the equivalent pi-model.

I have found Ro to be RD//ro = (50*6)/(56) = 5.35kΩ (that part is correct according to the answer key.

where ro= VA/ID = 10/0.2 = 50kΩ

What I am having trouble with is the Avo and Gv.

I have the following:

ID = 0.5*Kn*(W/L)*(Vov^2)

subsituting values I get:

200 = 0.5*(400)*(10)*Vov^2

therefore Vov = 0.3162 Volts

gm = Kn*Vov

=(0.4)*(10)*(0.3162)

therefore Avo = -gm*(RD//ro)

= -(0.3162)*(5.3535kΩ)

= -6.76 (the answer is -2.14 V/V

Where did I go wrong? Any help would be appreciated!