3-15
Figure 3-10D.—Tunnel diode schematic symbols.
Varactor
The VARACTOR, or varicap, as the schematic drawing in figure 3-11 suggests, is a diode that
behaves like a variable capacitor, with the PN junction functioning like the dielectric and plates of a
common capacitor. Understanding how the varactor operates is an important prerequisite to understanding
field-effect transistors, which will be covered later in this topic.
Figure 3-11.—Varactor diode.
Figure 3-12 shows a PN junction. Surrounding the junction of the P and N materials is a narrow
region void of both positively and negatively charged current carriers. This area is called the depletion
region.
