I
sent this email to ask one clarification on your book. This might be
minor but
I was just wondering
whether
there is a typographical error on page 767. Specifically in the
sentence :
“The
currents are equal in (c) because the SOURCE-GATE voltages of the PMOS
devices
are equal.”
Wouldn’t
it be more appropriate if we change it to
“The
currents are equal in (c) because the SOURCE to DRAIN voltages of the
PMOS
devices are equal.”
to
emphasize that the purpose of the op-amp is to make the VSD of both
PMOS
transistors equal ?
The
source-gate potential controls the current flowing in the MOSFET and
VSGs are
hard-wired
together
in (c). To precisely match the currents, as discussed in Ch. 20, you
also want
to try and
make
the source-drain voltages equal. This minimizes the effects of MOSFET
output
resistance. Yes
it
would be better to add
"The
currents are equal in (c) because the SOURCE-GATE and
SOURCE-DRAIN voltages
of the
PMOS
devices are equal."