so I am looking at this component and wanna make sense of how it does calculate the loop gain.
from here we have
(1) in1 = out1
(2) (in1 - out1)*CMDM = in2 - out2, but from (1), that yields in2 = out2.
so far, all reasonable, since we broke the loop, and these variables are equal. What I need to understand is finj, so from PCCCS, I think we can write for the current that injects to out2,
(3) the current the "iprove vinj" has times CMDM?
i need help to understand 
and how this essentially calculates the loop gain from stability analysis?
Also is CMDM=1 differential or common-mode stability?
Thanks!