The term *operational amplifier* was coined in 1947 to describe
differential amplifiers of high gain capable of amplifying DC signals
as well as AC signals.
The differential nature of these amplifiers simply means that we're
amplifying the difference between two input voltages.
We will show a generic operational amplifier (op-amp) as in
Figure 3.

**Figure 3:** An Operational Amplifier

In our analysis of this amplifier, we will make the following simplifying approximations to the model:

- The gain is infinite. That is `` .''
- Since no real device can produce infinite output voltage, this means that the differential input voltage must be zero. Or . (Hence, the quotes on the equation describing the gain.)
- Furthermore, we will assume that the current in both the positive and negative input circuits will be zero ( ).

Fri Mar 14 11:57:03 CST 1997