I'm trying to protect a receiver from spikes on the antenna from a nearby transmitter by using a PIN diode from the center conductor of the feed line (RG6, 75 ohms) to gnd. the receiver input limit is 1 dBm (1.3 mw}. Will Z × W = V2 give me the correct breakdown voltage spec?
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\$\begingroup\$ What frequency are you operating at? \$\endgroup\$– Andy akaJul 1, 2013 at 19:28
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2 Answers
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I think this is a difficult challenge to get decisively below 0dB and this is what i found along the way: -
Here is a decent article from SkyWorks about protection using PIN diodes and for lower frequencies using schottky diodes. It's pretty much encapsulated in the diagrams below:-
If you look at the 2nd graph down (single stage limiter using PIN) the maximum level coming through is going to be about 11dBm and this is 10dBm above your receiver limit.
However, the 2-stage detector limiter is going to operate at about 0dBm so maybe this is what you should be implementing. Read the blurb!
If you look at the Avago ASML-5822 it is a single stage limiter with schottky and it can only manage about 3dBm limiting so it looks like a 2-stage circuit is your best bet unless you are operating sub UHF where you will probably make a limiter with back-to-back schottky diodes as per figure 4 on the picture. However, it's going to be about 1.4Vp-p which is still about 10dBm so good luck hunting.
I'm at the extent of my knowledge on this area so I'd wait for an answer that makes better inroads into getting the limiting power sub 0dBm. I'll be doing the same.
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@Skip. An anti-parallel Schotkky limiter will turn on (P1dB) at ~0dBm. The turn on threshold is dependent on the diode barrier. The limiter circuit below has an inductor which is added to integrate the diodes' parasitic capacitance into a low pass PI network in order to minimize high frequency loss. The inductance value allows the low pass cut off frequency to be optimized for your max frequency.
@Andy aka.
However, the 2-stage detector limiter is going to operate at about 0dBm so maybe this is what you should be implementing.
The Schottky diode in fig. 16 senses the RF via a directional coupler. So, the threshold is 0 dBm if the coupler has a 0 dB coupling factor (k). But a 0 dB coupler doesn't exist. For other k values, the threshold is raise by the same amount in dB.
