Some Useful Operational Amplifier Circuits

Circuitsville Engineering has been actively collecting useful op amp circuits for many years. A really good resource is the National Semiconductor Application Note AN-31 which has a long list of possible opamp schematics.

One of the circuits on AN-31 is really useful when working with an Anadigm IC. In an Anadigm, the inputs and outputs are differential, which is useful but not universal. Being able to convert from Single Ended signals to Differential signals and back again is a skill to keep handy.

But first, consider the Difference Amplifier in the figure below:
In AN-31, VC is ground, so the output is simply the difference of VB and VA.
But, what if VC is a different voltage than ground?

In the first case the INPUT is added to the VMR, the reference signal at the center of the common mode range of the Anadigm IC. In the second case the INPUT is subtracted from VMR. Thus the two outputs together are a Differential Signal centered around VMR. Perfect for the differential inputs of the Anadigm.

Wonderful, but how about the differential output signals from the Anadigm?

This takes the difference between the two outputs OUTnP and OUTnN as a differential signal would. And it shifts the signal down to be centered around ground, provided that the op-amp has positive and negative supply voltages.