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."