I have read an interesting formula that says that
\$\mbox{Gain of an amplifier} = \dfrac{\mbox{resistance connected at the output}}{\mbox{total resistance between source and gate of the amplifier}}\$
Well, this has simplified the gain calculation and helped me avoid the small signal analysis which proves to be cumbersome in quite many cases.
But I was wondering how to manage the sign in the expression, i.e. let's say for the common source amplifier the gain has a negative sign before it but the common gate amplifier has a positive sign before its gain formula.
What is the significance of the sign?
I am here referring to the MOSFET common source amplifiers and the common gate amplifiers.