envelope follower

[Rene Schmitz]

At 21:22 30.09.1997 EST, you wrote:
>> Date:          Tue, 30 Sep 1997 22:52:14 +0200
>> From:          Rene Schmitz <uzs159 at ibm.rhrz.uni-bonn.de>
>
>> To detect the amplitude of the signal u~ =Uo*sin wt
>> you need a squaring circuit, that produces Uo^2 sin^2 wt,
>> you phase shift the input signal 90  by an integrator( RC=1/w ),
>> so that you get Uo * cos wt
>> a second squarer gives Uo^2 * cos^2 wt, you sum the both voltages,
>> and use a root circuit at whose output you get the Amplitude as a constant
>> voltage.
>>
>I haven't thought this through completely, but...
>The output voltage of an analog integrator is frequency dependant.
>The higher the frequency, the lower the peak-peak output voltage.
>
>So doesn't this mean there is a small snag in the circuit?
No, its just that you want something from the circuit which it can't provide!

>( Of course, small snags are what makes designing anything so much of
>a challenge.)
>
>:)

Nononono! The thing is you measure an amplitude of a signal whose frequency
you *know*,
and you design the circuit for exactly and only that frequency, and it has
to be a sinewave. (So it is more an AM demodulator; fixed carrier; variing
amplitude)
This was what was assumed in the earlyer post. (Divided audio bands...)
Ok, I should have said this more clearly, but it can be seen from the maths!!
Erm, thats what I meant by *discrete* frequency.

For everydaylife envelope detection of i.e. music you could/should use the
other circuit 
I described in my previous post!

Hope this clears the confusion.

Bye 
  René