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Barkhausen Criteria (Effect) and Vo, new= A(V+ - V-) for a OpAmp

L{V+(s)}/L{Vo,old(s)}}=
L{V-(s)}/L{Vo,old(s)}=
for example, 1r-1c wbo
L{V+(s)}/L{Vo,old(s)}= s/(s+a)
V-(t)/Vo,old(t)= R4/(R3+R4)