FET Small Signal Analysis

ENGI 242

ELEC 222

March 2003 FET Small Signal Bias 2

gm at Q

March 2003 FET Small Signal Bias 3

gm varies with VGS

GSm m0

P

DSSm0

P

V g = g 1 -

V

2I g =

V

March 2003 FET Small Signal Bias 4

FET Small-signal Equivalent Circuit

March 2003 FET Small Signal Bias 5

FET small-signal equivalent circuit that accounts for the dependence of iD on vDS.

FET Small-signal Equivalent Circuit

March 2003 FET Small Signal Bias 6

Determination of rd

March 2003 FET Small Signal Bias 7

Determination of rd

March 2003 FET Small Signal Bias 8

Common-source Amplifier

March 2003 FET Small Signal Bias 9

Common-source Small-signal Equivalent Circuit

March 2003 FET Small Signal Bias 10

March 2003 FET Small Signal Bias 11

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CS Amplifier Voltage Divider Bias

March 2003 FET Small Signal Bias 12

vo(t) and vin(t) versus time

March 2003 FET Small Signal Bias 13

Gain magnitude versus frequency

March 2003 FET Small Signal Bias 14

Source Follower

March 2003 FET Small Signal Bias 15

Source Follower Small-signal ac Equivalent

March 2003 FET Small Signal Bias 16

Source Follower Output Resistance

March 2003 FET Small Signal Bias 17

Common Gate Amplifier

March 2003 FET Small Signal Bias 18

CG AC Equivalent Circuit