VC envelopes

[Martin Czech]

> Consider a dual OTA such as the LM13600.  OTA #1 is configured as a normal
> VCA.  OTA #2 is gain controlled by the same signal as OTA #1, but it's
> input signal is a constant voltage provided by a reference source and a
> trimmer.  Now the CV feedthru should appear on both OTAs, so couldn't the
> output of OTA #2 simply be applied to OTA #1 at the inverting input?
> Would that not cancel most of the CV feedthru?  These parts are rather

If you look at the harris (ca3280 ?) dual ota data sheet (or app note) 
you'll see this idea applied for a sine shaper. 

But: the corrective current is added at the end of the circuit, ie. the
current to voltage converter (in this case a simple R).
I have the feeling that the error will cancel better this way.

m.c.

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