I have just been working through the math for shunt derived shunt
applied NFB around an amp and Ican't get the expected result.
Imagine an inverting amp with an open loop gain of -Ao with a feedback
resistor from output to input of Rf and an input resistor from signal
source to the input of Ri. I get a closed loop gain of:
An = Ao/(1+(Ri/Rf)+(Ri.Ao/Rf)) when I expected some thing of the form:
An = Ao/(1+ß.Ao) where ß = Ri/Rf
but instead I get Ao/(1+ß+ß.Ao)
I have checked the math several times and cannot see where I have gone
wrong. Anyone throw any light on this?
Cheers
Ian
