Are
the PMOS loads in Fig. 24.21 called
"composite cascodes?"
As
mentioned on page 636 a cascode
structure is formed by CASCading
a common-source
amplifier
(common-cathODE
from tube days) with a common-gate amplifier (common-grid
amplifier).
Hence the name CASCODE.
Since
the devices M3T, M4T, and M7T in
Fig. 24.21 are operating in the triode region (not
common-source
amplifiers) it would be
incorrect to call the PMOS devices seen in that figure
cascode
structures. A correct name is
"split-length" devices since the resulting devices are
really
just one MOSFET with an
effective channel length equal to the sum of the two
MOSFETs
(e.g., M3 has a W/L of 100/2,
see problem 6.14 on page 160).
Further,
the devices M3B, M4B, and M7B
don't have their gates connected to AC ground
so
they are not common-gate amplifiers.
Again, a split-length device should not be called a
"composite
cascode" since
it's not a cascade structure.
Note
that the structure seen in Fig.
20.35 is also a split length device. It's not a "composite
cascode"
device with 4 levels of
cascoding!