#### TicTek

##### Junior Member level 1

SO I am reading this article on negative feedback and the criteria to be stable.

I have not fully understood why if the loop gain at -180degree if the loop gain is less than 1 can be stable. why? because for me when the feedback has a shift phase of -180 and even the loop gain is less than 1,lets suppose 0.5 it will still add to the V+ since Vin=V(+)-V(-) and V(-)=A*B*Vo, A*B=-0.5(A=-1,B=0.5), so if I can run a simulation now as following

1. V(+)=1, V(-)=0, Vin=1, Vo=A*Vin=-1

2.V(+)=1,V(-)=(0.5)*(-1)=-0.5, Vin=1.5, Vo=-1.5

3.V(+)=1,V(-)=(0.5)*(-1.5)=-0.75, Vin=1.75, Vo=-1.75

so as you can see even it is increasing not so much but still it is increasing and not stable.

I know I have a lack in my logic here, so where I did not get it right?

Introduction to stability