On this page we will pull together
all of the Microwaves101 content on diodes.
Diodes are two-terminal, nonlinear
semiconductors used for generating, mixing, detection, and switching
of microwave signals. The first diodes were point-contact diode
used in crystal radios, 100 years ago. The schematic symbol for
a diode is shown below.
In general, diodes will conduct
when the anode voltage is higher (more positive) than the cathode
voltage. Most diodes used in the microwave industry are made on
silicon, but in some applications gallium arsenide (GaAs) is a better
So far we have some content on:
diodes (new for November 2006!)
Step recovery diodes
diodes used in switches
Microwave diodes com in a variety
of package styles, as well as configurations, such as quads, and
anti-parallel pairs. The high-frequency limitation of most diodes
is their junction capacitance. The key to microwave performance
is to minimize package parasitic capacitance so that it doesn't
make the capacitance problem worse.
Beam-lead diodes are formed by
growing diodes with gold interconnects, then removing substantially
all of the semiconductor material so that the diode is left with
gold tabs that can be welded to gold traces on circuits.
Stud-mounted diodes are useful
for waveguide applications. The "stud" containing the
diode is threaded and can be screwed into a hole tapped in a waveguide
Diodes can be delivered as chips.
Here one part of the diode is grounded to the silicon chip, and
the other serves as a wirebond pad. Often the pad size is extremely
small, and you have to be very careful not to create a ball-bond
that is bigger than the pad or the capacitance will be increased.
Plastic-encapsulated diodes are
available, but these are limited in frequency response because of
We'll add some pictures just
as soon as someone sponsors this page!