LM13600 VCOs in Spec Sheet

Haible_Juergen#Tel2743 HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de
Wed Oct 11 00:59:00 CET 1995

>I have played with them, but that was almost 15 years ago. The only
>thing I remember was that the VCO drifted a lot. As can be seen from
>the design equations, the transconductance is heavily dependent on
>temperature, even without an exponential converter.
>For serious VCOs I'd recommend the Electronotes designs, or discrete
>types such as those in the Odyssey, SEM or Prodigy.

Without having either circuit in front of me maybe I can just add
something general:
To avoid dependence of gm, the input of the OTA simply has to be
quite overloaded, i.e. the long tailed pair inside just acting as as
*switch* for the current that is forced into the emitters. Then the OTA's
output just switches between the positive and negative value of
the control current. I guess that's how the EN circuits work.
But are the app note circuits really that different, concerning this ?


PS.: always take care that the differential input voltage is limeted to
+/-5V while Your overdriving the input!

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