Gain from the input resistor becomes zero. But, it turns into a
non-inverting, unity gain amp relative to the plus input of the amp.
Inverting gain = Rf/Ri = 0/Ri = 0. Non-inverting gain = Rf/Ri + 1 = 0/Ri + 1
It always amazes me... the little things you can learn from the most
basic books and articles. Like... no one ever told me god created
PNP transitors. Is this more persecution, Dr. Laura, and how should
I smite them?
Seriously, I have a real basic book which wouldn't have taught me
much except that it has a chapter on components. Different types of
Rs, Cs, etc. Or there's my physics book that's short on words and
big on equations contrasted with an EE series (9 volumes) which
covers 1st year physics with more explanatory words. It just adds a
You get a zero-gain inverter. I saw one of these in use once, and
my engineer was baffled by it. "What the heck is a zero-gain inverter
for?" and you could almost see the question marks around his head
like in the cartoons.
It provides a virtual ground. I believe that the reason for doing
it that way has something to do with temperature compensation or
input offset current of the downstream devices.
Or, if you lift the non-inverting input, it's a voltage follower.