
Ampliers: Basic MOSFET Congurations
463
" "
R
v
i
def
oMOS
ds
d
Ropen
L
" "
R
v
i
def
o
ds
l
Ropen
L
" "
R
i
def
oMOS
ds
d
Ropen
L
With the condition of
s
!
=
, the current g
m
v
gs
= 0, so that the voltage
controlled current source (VCCS) results open. As a consequence,
R
oMOS
= r
o
"
R
v
i
def
o
ds
l
Ropen
The overall output resistance is easily determined as
||
oo D
The output resistance is typically large, so that a voltage buffer is necessary to
drive a low load resistor.
12.2.2.3
C
.S.: Voltage G
a
in
The voltage gain A
v
of the amplier in the mid-band frequency regime refers to
the ratio between the output voltage v
l
, across the load resistance, and the input
voltage v
s
of the ...