Mark Rages wrote:
> AD620: 30=B5V input offset voltage
> LM324: 2 mV input offset voltage
>
> How big is the signal you're trying to measure?

That's not the issue since DC offset doesn't matter.  You are looking for a
AC signal and can AC couple the input with a sufficiently long time
constant.

However, take a look at the common mode rejection ratio of the AD620 and
compare that to anything you can even hope to get with some LM324 amps and
discrete parts.  The AD620 has something like 100dB common mode rejection i=
f
I remember right.  That's a voltage factor of 100,000.  That means a 100V
common mode signal won't look like more than 1mV of differential signal (no=
t
that the AD620 can withstand 100V input).


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