PIN diode - self biasing limiter?
I was having problems with using an antiparallel pair of PIN diodes as a limiter. The diodes were shunted between the RF line and ground. Since the turn on voltage is 0.76V, I expected the diodes to turn themselves on when the RF signal was > 8 dBm. They did not turn on.
PIN diodes can not rectify high frequency f>>1/(2*pi*transit time) signals. Therefor the diode can not develop the DC bias to turn itself on. PIN diodes are great at RF because they don't act as rectifiers, and instead appear as current controlled resistors.
For the simplest limiter, I should replace the PIN diodes with schottkys. The schottky diode turns on at a much lower voltage 0.3V. Therefor, I have to apply reverse bias to the schottky to make it turn on itself at a higher power level.
The challenge is then to ensure a low parasitic path to AC ground.
posted by MyTravels @ 6:03 PM
2 Comments:
A better approach maybe to use your antiparrallel PIN diodes, but place a quarter wave lumped element network (or trace, depending on your frequency of operation) in front of it. You then simply need to supply a DC current to the PIN to ground to make the circuit appear as an open to the incoming power. You should be able to obtain ~30dB of isolation with this method. Need more isolation?, cascade multiple quarter wave + PIN diode sections.
Thanks for the comment. I'm not sure how well your solution would word for a broadband input from 10 0khz to 9 GHz.
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