Re: Low-C input protection diodes

john jardine wrote:
"Joerg" <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:do6Ti.59379$Um6.28222@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hello Folks,

What's the low cost and most of all low capacitance diode pair du jour
for protecting RF chip inputs? My staple is the BAV99 or BAV199 but
above 500MHz the 3-4pF of a pair begin to matter. Can't bias them much
because there ain't a lot of VCC to begin with.

Recovery time doesn't matter as long as the stray inductance is low so
the diode kicks in the nanosecond a spike wants to come in. They should
be able to stomach something around an amp once in a blue moon. Series
connection, of course. If it has to be singles, ok.

I was pretty surprised to learn that some RF chips have internal
coupling caps but almost zilch in terms of protection. Consequently a
client of mine has them die like flies. Why are RF chip inputs so
fickle? For example, the Linx datasheets often just state abs max at
0dBm. Great. That's not much of a consolation for anyone who has to
deploy in a rough environment.

--
Regards, Joerg

http://www.analogconsultants.com/

Neither dual, or 1 amp but in R.F. use I've never killed a low C, low Vd,
BAT81.


You mean the BAT18 PIN Diode? That one comes as a dual and is called BAT18-04 for the series pair. But as with a lot of EU parts no stock at Digikey. Also, its capacitance is about the same as that for the old BAV99.

I've killed a lot of RF stuff because sometimes I get involved in power designs. Things like turning the ceramic of a resistor or cap into bubbly green glass. Mostly they look kind of cool after the smoke has wafted off.

--
Regards, Joerg

http://www.analogconsultants.com/
.

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