Op-amps are direct coupled devices such that the input signal may be either AC or DC,
or a combination of the two. The industrial standard op-amp, the 741, requires two power
supplies, one positive and one negative. For most applications the magnitude of these two
voltages is the same. All op-amps have two inputs connected in a differential mode, so that
output voltage is Vo= A(V+ - V-) where V+ is the voltage at the non-inverting input and V- is
the voltage at the inverting input. A is the open loop gain of the op-amp.
The circuit symbol for an op-amp is shown in Figure 6.1. The pin connections for the 8 pin DIP
package µA741 op-amp are given in Figure 6.2.