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PIN Diode Switches

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An excellent primer on PIN diode circuit design is available on the Skyworks Solutions Inc. site

Here's an important consideration for designing with shunt switch elements that you need to know about!

New for June 2020: the video below is a tutorial on PIN diodes used in switches, by Alan, a Ham Radio enthusiast (W2AEW).  Alan explains how PIN diodes work using pen and paper, then constructs and demonstrates a SPST series with about 25 cents worth of components.  He provides information on how to design shunt, and series/shunt SPST PIN diode switches and multi-pole designs. He even hits on a transmit/receive switch that has a single control voltage, using a quarterwave trick. The main point you should take away from this video is the real magic of PIN diodes: for a relatively low DC current, a much larger AC current can be switched.

Microwave circuit design being a thing all its own, it is interesting to see someone in the "RF world" (say, below 500 MHz) applies the same fundamental principles with different techniques. For example, who among us would have thought use a Tektronix 2465A oscilloscope to observe the behavior of a PIN diode?  And what microwave engineer uses a BNC cable to carry RF?  Aren't those just used for DC supplies out in the lab?

It is awesome to see the low frequency characteristic of PIN diodes on display in the time domain,  Why pay $50,000 for EDA software to simulate large signal behavior when you can actually watch it? Seeing the difference in performance at 10 MHz and 1 MHz is a great lesson in why PIN diodes have a lower frequency limit: they run out of stored charge and start to distort (start around 8:30 into the video). Looking at the clipped response, you can tell that PIN diodes can be configured as frequency multipliers, but that is a subject for another day.

One correction and a comment: Alan points out at 2:40 and 13:50 into the video that RF resistance varies linearly with diode forward DC current. The opposite is true; diode conductance is proportional to DC current.  Also, don't think that you can reduce RF resistance to pico-ohms by increasing the current from milli-amperes to amperes... the diode will burn out from power dissipation due to the forward voltage drop, probably south of 100 mA.

Enjoy!

#118: Basics of PIN diodes and their use in RF switch applications, by Alan

Alan's Youtube channel has 300 videos, tutorial in nature, dealing with basic electronics, circuit design and analysis, test & measurement, and ham radio.

 

Author : Unknown Editor

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