"Winfield Hill" -edu wrote in
message ...
For example, these plots show that an ordinary 1n4148 class of silicon
signal diode, which conducts about 0.5mA at 600mV, is still working at
250mV, conducting 1uA in my measurements. In fact, this diode was still
conducted at 100mV. See http://www.fairchildsemi.com/ds/1N/1N4148.pdf
where Fairchild's datasheet also shows this exponential relationship,
albeit drawn with a draftsman's straight line.

So, as others have pointed out, diodes can rectify very small signals.
They may not be very efficient, but they will work. These plots also
show how Schottky diodes (e.g., 1n6263 and 1n5819) are better than
ordinary silicon diodes at low voltages, even below 100mV. The 1n6263
may be hard to get, but other parts, like the sd101 or bat17 may not.
http://www.vishay.com/docs/85629/85629.pdf

There are other diodes that work well at very low voltages, notably
some made by Agilent (see an1090), but we won't go into them here.


--
Thanks,
- Win


Must be my lucky week!. I needed to make some similar readings. Thanks!.
I still puzzle over the oft quoted "up to about 30mVrms the output from the
diode offers a square law response and will approximate a true RMS
measurement.
As the OP found, there's very little happening down there. Who makes these
sweeping statements?.
regards
john