You don't say if this 10mv is sub level of a larger DC, nor do you
say if it's DC or AC ?
So for the moment, I'll assume it's a 10mv DC base line that you want
to squelch out
Pass the 10mv into something like an op-amp first stage pre amp.
A gain of 10 would then bring this signal to 100mv. The output
would then be a reference to use on a comparator which can be used
to switch something on/off..
A comparator, being that the output on most that i've seen are
open collector, will let you easily integrate this into a analog
switch.. For example, a T bar Diode switch can be used where the
comparator output (via a R load) would supply the center bias for the
switch via
Freq response time, max input and things like that has to be known..
P.S.
On the preamp stage, you wrap the loop back gain with a zener to
avoid over drive on the input.
It's seems to be a trivial problem, but maybe there are some
constraints you are not mentioning here?
Jamie.
Thanks folks for the responses.
It's a dc input, which has to be measured down to 10mV, to an MCU
successive approximation AtoD. However the signal can go negative by a
diode drop, say -0.6V. The input has a schottky diode holding it to
-0.2V.
However the MCU gets the measurments wrong when the input goes to
-0.2V. I don't know the mechanism and at the moment I don't know if it
is this input or another input that is screwing up.
I do know the MCU makes the wrong decisions. If the input is clamped
to 0V when at -0.2V everything works OK. The board is in China so I
was looking for a cludge they could try to prove the point.
I didn't think matched diodes would work but it was worth asking the
question. John gave me an answer that told me to look at other
solutions. I've gone for a 2 transistor circuit driving a FET to
clamp the pin when the input goes negative, and removed the schottky.
I'll know by breakfast whether that has worked.
I am curious how -0.2V can screw the Samsung MCU AtoD. It's not enough
to forward bias the catch diodes but if it got into the substrate it
could change the voltage range. I wondered if the comparator in the
AtoD was doing a phase reversal due to the negative input but it seems
unlikely.
It's an interesting challange sorting out the Chinese, it's a shame it
has to be done under time pressure.