[sdiy] CA3080 switch driving voltage

[jhaible]

I remember I've seen this somewhere (Electronots?), but
I don't remember _where_.

If you build a triangle VCO core,
opamp integrator, 3080 providing the integration current,
schmitt trigger to switch the 3080's current direction,

what is the optimal voltage and impedance to drive
the 3080 input, in order to get the best linearity
of frequency vs. control current ?

At first, you might think maximum overdrive with
low impedance would be best (like 5V and 0 Ohm)
to get immediate switching (no RC time constant
with parasitic C's), but apparently such a configuration
is "too much" and degrades the linearity of
Iabc -> Iout operation. (Yes, speaking of switching!
Maybe base current? Maybe too much common
mode signal? Don't know ...)

So, where is the optimum? I vaguely remember
a resistance of a few hundred ohms, but I
don't remember the voltage at all. Certainly
more than 100mV, certainly less than 5V.

JH. (Working on an improoved version
        of the FS-1)