
Principles of Analog Electronics
468
12.3.2.3 C.D.: Voltage Gain
The MOSFET’s KVL expression gives
gd gs sd
and the analysis of the AC equivalent model of Figure 12.14 gives
|| || || ||vgvr RR gv vr
sd mgso SL mgddso
==−
1|||
|||
+
=vgrRRvgr
sd mo SL gd mo
Therefore,
A
v
v
gr
gr
|| ||
1||||
def
vMOS
sd
gd
mo
mo
)
(
=
+
Since the occurrence of
|| || 1gr RR
is often veried,
vMOS
, hence
the name source follower.
Now, the overall voltage gain must take into account the attenuation factor
due to the input voltage divider:
,
vi
G
so, nally
|| ||
1||||
A
gr RR
gr RR
R
v
mo SL
mo SL
G
)
(
=
12.4 C.G. CONFIGURATION
In a common ...