[time-nuts] TAPR TICC boxed (input protection)
csteinmetz at yandex.com
Thu Apr 6 22:23:43 EDT 2017
> I know one thing to watch out for if you are looking for low
> leakage is gold doping
Anything that increases carrier mobility increases leakage current (all
else equal -- i.e., for each particular device geometry). This accounts
for the much higher leakage of Schottky and germanium junctions.
> Out of curiosity, and I tried to look this up years ago, what doping
> is used for PNP RF transistors and saturated switches if it is not
> gold? Does it also increase leakage?
Gold doping doesn't affect the speed of BJTs in the active region very
much -- its purpose is to reduce minority carrier lifetime and, thereby,
to reduce storage time when a transistor recovers from saturation. I'm
not sure how manufacturers deal with this in the case of PNPs. [Note
that the list of fast PNP small-signal switching transistors is very
short, and the fastest of them are slower than the slowest fast NPN
> And I have another question if you know. How is rb'Cc measured?
One way is to drive the transistor with a medium-high frequency (well
down the 1/f portion of its current gain curve -- typically 10-50MHz for
small-signal BJTs) and measure the base-collector phase shift. It can
also be calculated from fT and Cc-b. There is a JEDEC standard for
measuring rb'Cc, but I'm not finding my copy at the moment. It may be
posted on the JEDEC web site.
> The advantage of the 4117/4118/4119 is that the leakage is already
> tested to a given specification so no qualification or testing is
That may be true, but there is nothing in the data published by Vishay,
Fairchild, Calogic, or InterFET to indicate this. Spot-checking, along
with the part design, should be sufficient to guarantee meeting the
spec. I'll try to remember to ask the Vishay process engineer next time
I talk to her.
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