by "Ian Iveson" <IanIveson.home@[EMAIL PROTECTED]
>
Apr 23, 2008 at 03:07 AM
Ian Thompson-Bell wrote
> I have just been working through the math for shunt
> derived shunt applied NFB around an amp and Ican't get the
> expected result.
Is that the same as voltage derived, current applied? I can
never remember this stuff, sigh.
> 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?
Your maths is correct or we're both wrong.
I don't know if it helps to see it as Ao/(1+ß.(1+Ao))
You haven't explained why you believe there is an anomaly.
What led you to your erroneous expectation?
Ian
