Figure 1-8.Adding stages of amplification.
Whether an amplifier is one of a series in a device or a single stage connected between two other
devices (top view, figure 1-8), there must be some way for the signal to enter and leave the amplifier. The
process of transferring energy between circuits is known as COUPLING. There are various ways of
coupling signals into and out of amplifier circuits. The following is a description of some of the more
common methods of amplifier coupling.
The method of coupling that uses the least number of circuit elements and that is, perhaps, the easiest
to understand is direct coupling. In direct coupling the output of one stage is connected directly to the
input of the following stage. Figure 1-9 shows two direct-coupled transistor amplifiers.