AW: Envelope follower schamtic

Haible Juergen Juergen.Haible at nbgm.siemens.de
Tue Jun 24 12:03:43 CEST 1997


	>this is ingenious....i cant read german either, but it looks
like the first
	>section acts as an unfiltered full wave rectifier so that the
frequencies
	>are doubled, which makes the filtering more effectiv in the
second
	>section......i wouldn't have thought of that on a million
years....

I can read German, but I only got the first half of the text (Reload
didn't help).
Using two rectifiers is an old trick - I have seen a circuit in
Electronotes
which uses even more than two rectifiers in series. The good thing of
this specific circuit is its minimum part count !
The NE57x devices are single supply chips, so you need the offset 
voltage at the final opamp stage, as shown in the circuit. I wonder how
stable the offset voltage is  (temperature dependency ?) If you want to
use envelope followers on signals with large dynamics, zero offset is
crucial.
And using only one capacitor for smoothing might not be the best choice.
Maybe the final opamp should be configured as an dditional 2-pole LP
at least.

JH.
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