EE PRO for TI - 89, 92 Plus
Equations - Linear Amplifiers
107
Rin
Rl
rd
=
+
+
b
g
µ
1
Eq. 28.5.2
Av
gm
rd Rl
rd
Rl
= −
⋅
⋅
+
F
HG
I
KJ
Eq. 28.5.3
Ro
rd
=
Eq. 28.5.4
Example 28.5 -
Find the voltage gain of an FET configured as a common-source based amplifier. The
transconcductance is 2.5 x 10
-3
siemens, a drain resistance of 18 k
Ω
and a load resistance of 100 k
Ω
. Find all the
parameters for this amplifier circuit.
Entered Values
Calculated Results
Solution -
Use all of the equations to compute the solution for this problem. Press
„
to display the input screen,
enter all the known variables and press
„
to solve the equations. The computed results are shown in the screen
display above.
-PQYP8CTKCDNGUIO
AUKGOGPU
TF
AM
Ω
4N
AM
Ω
%QORWVGF4GUWNVU
#X
µµ
4KP
A
Ω
4Q
A
Ω
28.6 FET (Common Drain)
The first equation defines the amplification factor
µµ
in terms of transconductance gm and drain resistance rd. The
second equation computes input resistance Rin as a function of load resistance Rl, rd and
µµ
. Voltage gain Av is
defined in the third equation. The final equation computes the output resistance, Ro.
µ =
⋅
gm rd
Eq. 28.6.1
Rin
Rl
rd
=
+
+
b
g
µ
1
Eq. 28.6.2
Av
Rl
Rl
rd
=
⋅
+ ⋅ +
µ
µ
1
b
g
Eq. 28.6.3
Ro
rd
=
+
µ
1
Eq. 28.6.4
Example 28.6 -
Compute the voltage gain for a common-drain FET amplifier as configured in the previous
example. The transconductance is 5 x 10
-3
siemens, the drain resistance is 25 k
Ω
, and the load resistance is 100 k
Ω
.