Click here to purchase the entire book in PDF format. Leftovers There is one of the three characteristics of op amps that we mentioned up front that we haven't talked about since. This is the output impedance, which was stated to be 0 $\Omega$ . Why is this important? The answer to this lies in two places. The first is the simple voltage divider, the second is a block diagram of an op amp. If you look at the diagram in Figure 2.68, you'll see that the op amp contains what can be considered as a function generator which outputs through an internal resistor (the output impedance) to the world. If we add an external load to the output of the op amp then we create a voltage divider. If the internal impedance of the op amp is anything other than 0$\Omega$, then the output voltage of the amplifier will drop whenever a load is applied to it. For example, if the output impedance of the op amp was 100$\Omega$, and we attached a 100$\Omega$ resistor to its output, then the voltage level of the output would be cut in half. Figure 2.68: A block diagram of the internal workings of an op amp.