On Thu, 5 Dec 1996, Gregg Kricorissian wrote:

> Bernd,
>
> You asked:
>
> >I need this because the input Voltage is a sinodial Wave with a variable
> >Amplitude of only 3 to 10 milli Volts. I want to obtain a stabilized Wave
> with a
> >Amplitude of 2 Volts whitch has about +2.5V DC Offset (will say: the Voltage
> >varies between +0.5 and +4.5 Volt like a +2.5V shifted Sinewave).
>
> Perhaps I'm oversimplifying the problem, but I don't see whay you need AGC
> at all.
>
> Your main problem will be getting teh milivolt level signal out to the
> electronics, without picking up noise etc.  Use a balanced line, with
> shielded cable. If the environment is very bad, put a voltage amp right at
> hte source to drive the cable.
>
> Use whatever op amp you like, but for single supply applications, the good
> ol' MC 3403 (quad op amp) would be where I'd start.  Biasing the signal the
> way you want should be a piece of cake.  Once you've popped the signal to a
> decent level and gotten it out of the noise floor, you shouldn't have to
> worry about leveling it before feeding to a Schmidt Trigger.
>
> Hope this helps,
> .... Gregg
>

You can use a differential amplifier on the input to reduce noise.
Or better yet, split the signal into a differential pair
before sampling and sample differentially to obtain a better SNR.