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HOME > The Unusual Diode FAQ - Title Page > The Unusual Diode FAQ - IV.13 - Microwave PIN Diodes

I-V CurveIV.13 - Microwave PIN Diodes?

Here's a link to Microwave PIN Diodes at the University of Michigan.

This part contributed by Marshall Jose, Marshall.Jose@jhuapl.edu:

PIN diodes are useful for switching and attenuating RF (radio frequency) signals. Basically, between the P- and N-doped regions of the diode is an undoped region referred to as "intrinsic" (hence the I in "PIN"). When a forward DC bias is applied the diode, a large number of holes and electrons are created in the I region, allowing forward conduction. If the bias is suddenly removed, these charge carriers will take some time to recombine and thus stop the conduction of current. This amount of time is quite a bit longer than the time a normal PN diode takes to cease conduction.

All this means that while the PIN diode is conducting forward bias current, it will conduct a high-frequency signal superimposed on the bias current, too -- even a large signal which would cause a momentary reversal of diode current! Furthermore, the high-frequency signal won't be much distorted. The net effect of the diode at high frequencies is that of a variable resistor, whose resistance decreases as the bias current increases.

(Note that the phrase "PIN diode" can also refer to a range of power diodes with a very wide near-intrinsic region, which supports a high breakdown voltage. These are not microwave diodes.)