7. Solid-State Devices. Solid-state devices (sometimes referred to
as semiconductors) have, to a large extent, replaced vacuum tubes in
the design of most modern electronic equipment. Solid-state devices
are generally made of silicon or germanium that is "doped" with
impurities to provide the desired conductivity. They may be doped to
produce either p-type material (positive) or n-type material
These semiconductors are used in the place of vacuum
tubes due to these advantages: they are smaller, take less power to
operate, usually cost less, and are more rugged.
Probably the most common of these solid-state
devices is the transistor. While there are numerous variations, most
28 shows the symbol for a npn and a pnp transistor.
The key to
recognizing a npn or pnp is the direction of the arrow on the
the npn, the arrow points outward.
The elements of the transistor
operate much like the elements of the vacuum tube.
functions much as the cathode; the collector as the plate; and the
base much like the grids.
Transistors are labeled with the letter
NPN, PNP Transistors.
b. Diodes. Another common solid-state component is the diode. A
diode consists of one piece of p-type material and one piece of
n-type material formed together to create a p-n junction.
junction has the property to pass current in only one direction.
Diodes are also designed in a number of