The operational amplifier is one of the most useful analog ICs available, and one of the most daunting for beginners and experienced engineers.

Above is a diagram of an op-amp in a closed loop ~~non~~ inverting configuration. Probably the most used configuration. Lets assume this is an ideal amplifier. R_{1} is the input and R_{2} is the feedback. When R_{1} = R_{2} the circuit is in unity(meaning input = output).

To calculate output use the following formula.

–

R_{3} can be calculated by the following.

That is inverting.

In the above link the gain equation is missing a parenthesis someplace.

I retrace that last post. It was just a printing error on my end.

That is an inverting configuration, and with the + input at ground, you are going to need a split supply (both positive and negative voltages) and for a positive voltage in you get a negative voltage out. I don’t think that is the most common opamp configuration these days, people like single-supply circuits.

The semiconductor companies have produced all the free documentation

you’ll ever need about op-amps, including free books. Just google and read:

“Op Amps for Everyone”, TI

“Handbook of Operational Amplifier Applications”, TI SBOA092a

“Op Amp Applications Handbook”, ADI

The ADI book is available as a dead tree, but it’s also on their site.

Thanks for those recommendations, Jim.