Block diagram of CS-80 VCO chip online

[jh.]

> Well, talking about that some people are looking into
> application notes, this looks wery similary to the XR4151/LM331!!

Yes.
And in an old National Semiconductor book ("Intuitive IC opamps")
there is a schemo with a single LM301A, introduced as
"Some more of RAP's handiwork has provided the charge-dispensing
voltage-to-frequency converter shown in figuge ..."
Maybe that's a predecessor of the 331 ?
(I have no idea which was first, 4151 or 331.)

JH.