Figure below demonstrates the significance of correctly matching input and output impedances between stages of the circuit. The AC signal source demonstrated in the left half of our fig below could be the output of a common-emitter amplifier, a laboratory signal generator output, the “line”
output of a FM radio receiver, or numerous of other possible sources.
Here the important point is that all signal sources will possess an internal impedance; shown by Zs in the example. Internal source impedances can range from less than of an ohm to many thousands or even in millions of ohms in value. In this case, assume that the internal impedance is 1000 ohms. The signal level we want to supply to RL is 10 volts peak to peak. Notice that Zs is in series with RL. We know that, in a series circuit, the drop in voltage will be proportional to the values of resistance.
