
Basic MOS Device Physics
5
The transconductance can also be expressed as
g
C
W
L
I
I
V
m
nox d
d
eff
==2
2
µ
(1.6)
Interestingly, Equation (1.6) indicates that g
m
can be determined by the ratio of
the drain current (I
d
) to the effective gate-source voltage (V
eff
). What’s more, it is
possible to make the transconductance be independent of the value of (W/L) as long
as that ratio is kept as a constant. Hence, to a fi rst-order approximation, the scaling
of the transistor geometry does not affect g
m
. This is a desirable feature because the
voltage gain and accuracy can be maintained while the device is being downscaled
(however, this argument does not hold in ...