FET question

Martin Czech martin.czech at intermetall.de
Tue Nov 16 09:44:44 CET 1999

:::Is there a difference in the noise contributed by a FET when
:::it is used as a follower versus a common source amp?

The equivalent INPUT noise sources stay the same.  Since the gain can
be very different (follower ~1) the output noise can be very different
, too.  FET have superior noise performance if the signal source has
high resistance, (10k-100k), otherwise bipolar are better.

A slightly damaged fet junction may contribute additional popcorn noise.

I think the 1/f noise is also worse in FET, since they drift and age 
more then bipolar.


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