So far several circuits have been presented with the most varied configurations. However, the basic circuit has always used a single operational amplifier. Now in this chapter, we'll see how we can associate more than one operational amplifier.

We will start by presenting a basic circuit using two operational amplifiers in the inverting configuration. See the Figure 46-01, as it presents the circuit.

See, in reality, they are just two inverter circuits connected in series. Thus, to calculate the gain of this circuit it is enough to calculate the gain of each one separately and then join the two equations found.

For the first circuit we have:

And for the second circuit we have:

Substituting the first equation in the second and working algebraically, we arrive the final equation, or:

Note that when we associate two inverter circuits, the output signal has the same phase of the input signal, because multiplying two negative values we obtain positive values.

In the part about the problems, we will present other configurations of circuits in cascade with their respective solutions.