# op amp rails and its inputs

I am trying to feed this voltage measured by the oscilloscope to a voltage comparator. By design the voltage should swing between +0.7 and -0.7. BUT since the voltage is not referenced to ground I am really having a hard time wrapping my head around what should be connected the comparator, and HOW should I connect them.

Since the voltage am trying to feed to the comparator is not referenced to ground, I can't just get away with connecting the op-amp negative rail to ground right?

Just bear with me one more moment, what I am trying to say is if for instance I feed a signal that has a magnitude of 0.7 does that mean it's 0.7 higher in voltage than the op amp ground, or is it independent of the op-amp ground? I mean if for instance I connected the comparator negative rail to 0.7V and then feed a 0.7 to any of the inputs would I be effectively feeding the op-amp 0 volts since they are both at the same level. So I guess what am trying to ask is, what are the relation between the + and - rails of the op-amp to it's inputs. what should I connect the - and + rails of the comparator. I am really confused about what a ground represent in this case.

• The question talks about op amps, but there isn't a single op amp in the schematic. Show us the full circuit. Jul 1 '15 at 17:12
• The inputs must be < than the V+ and > than the V-. For rail to rail amps the rail voltages are included in the acceptable range. There are some op amps that go slightly beyond rails for inputs, but most don't. Jul 1 '15 at 17:35
• i am trying to build this circuit i want to feed the voltage measured by the oscilloscope to an op amp working as a comparator, but i haven't yet figured out how it should be connected and that's why it's not in the schematic Jul 1 '15 at 17:36

Anyways, a comparator outputs it's positive rail voltage when it's positive input is greater than it's negative input. It outputs its negative rail voltage when the positive input is less than it's negative input.