MOSFET Drain Current and AC Solution Analysis - Prof. William Leach, Study notes of Electrical and Electronics Engineering

Download MOSFET Drain Current and AC Solution Analysis - Prof. William Leach and more Study notes Electrical and Electronics Engineering in PDF only on Docsity!

Common-Source Amplifier Example

K

prime

0.002 W 1 L 1 V

TO

1.75 λ 0.016 χ 0

V

plus

24 V

minus

24 R

6 . R 2

6 . R D

3 .

R

S

3 . R 3

50 R

L

3 . R s

3 . R p

( x y, )

x y

x y

DC Bias Solution

V

GG

V

plus

R

V

minus

R

R

R

V

GG

= 16 V

SS

V

minus

R

SS

R

S

V

V

GG

V

SS

V

TO

V

We neglect the Early effect, i.e. set (^) λ = 0 to solve for the drain bias current.

K K

prime

W

L

I

D

2 K.^ R

S

2 .

1 2 K.^ V

. R

S

2

. I

D

V

D

V

plus

I

D

R

D

. V

D

= 7.454 V

S

V

minus

I

D

R

S

. V

S

V

DS

V

D

V

S

V

DS

V

GS

V

GG

V

S

V

GS

= 3.036 V

GS

V

TO

Because V DS

> V

GS

V

TO

, the MOSFET is in the active or saturated state.

Here is an exact solution for the drain current. Note that MathCad requires numbers for everything

except the variable being solved for. The drain-source voltage in the equation is 48 I D

3 .

I

D

3

. (^1) 0.016 48 I D

3

... 3000

2 .

3

. (^1) 0.016 48 I D

3

... .6.25. (^30001)

2

This is the exact solution for I D

including the Early effect. We will use

the approximate solution for the ac analysis below.

I

D

. (^100) = 3.567 This is the percentage error in neglecting the Early effect in

solving for the drain current.

G

mg

(^1) χ

r is

R

ts

r 0

r 0

R

p

r is

R

ts

i dsc

G

mg

v tg

. (^) i dsc

v o

i dsc

R

p

r id

R

td

. (^) v o

= 15.945 This is the voltage gain.

r out

R

p

R

D

r id

, r out

r in

R

p

R

R

, r in