Values and models are arbitrary. The circuit above was written on board (without values) as an exercise for "breaking the loop" method, however I do not agree with the answer which says the feedback factor is K = -Rf. I would say that K = Vrs/Iout where Iout is the current flowing out of Q1 and 1/gm is the resistance seen from the source of the mosfet:
from 2 current divider equations. I did find a similiar example from Razavi's CMOS Integrated Circuits book : 
which the answer was identical if you do not consider 1/gm. Now I have 2 questions:
- Why do we not consider 1/gm?
- In Razavi's example polarity of the feedback is negative and his feedback factor turned out positive which makes sense. However in my example the feedback should be positive which tells me the feedback factor should be negative. How do I get the minus sign that I am missing?
