A real *Operational Amplifier* usually has the following characteristics:

- Finite
*Input Impedance*. Its value depends by technology used to build the Op Amp. Usually it is about for*Operational Amplifier*whom first stage use*BJT*technology. It increases for*MOSFET*technology. Anyway this value is high enough to be considered, with good approximation and in most cases, infinite. - Non-Zero
*Output Impedance*. Usually its value is between and . This value is low enough to be considered, with good approximation and in most cases, equal to zero. - Finite Open-Loop Gain. Its real value is usually equal to but it can raise to . This value is high enough to be considered, with good approximation and in most cases, infinite.
- Finite
*Bandwidth*. Usually*Operational Amplifier*'s cutoff is near . Really bad! It implies that*Op Amps*can handle only signals with a bandwidth less than . This is a big limit. - Finite
*CMRR*. This value is high enough to be considered, with good approximation and in most cases, infinite. - Non-Zero
*Noise*. Unfortunately*noise*is always present in every electronic component.Fortunately building technology reduces it and its incidence is usually negligible. *Current OffSet*and*Voltage Offset*does exist and, in most cases, can not be overlooked. Fortunately it can be reduced to negligible values by means of a trick that we will see in the next lesson.

As you can see, in most cases, we can consider the behavior of the *Operational Amplifier* as if it were ideal.

Biggest problems are created by *Bandwidth* and *OffSet*.

In the first case, we just work with signals that have a bandwidth lower than .

In the second case we must operate on the offset correction's pins.

By now we consider these two aspects as negligible.

We will assume that signals have an adequate *Bandwidth* and that *OffSet* problems have been adequately corrected.