[sdiy] VCO Linear Voltage

[Magnus Danielson]

David G. Dixon wrote:
> Oh...my...Gawd!!!!
> 
> Yes, the current conveyor is just the ticket for sending a current into any
> arbitrary voltage unaltered, and will indeed allow the SSM2164 to have "safe
> sex" with the LM13700.
> 
> And, what is the simplest, most straightforward implementation of the
> current conveyor...?
> 
> a Supertransistor!
> 
> ...which is just a transistor on the end of an opamp!  The current is fed
> into the opamp's - input, the + input is grounded (thus providing virtual
> ground at the - input), the opamp's output feeds the base, the emitter is
> fed back to - input, and the collector sources or sinks (depending on the
> transistor type) virtually the same current to whatever voltage.  Hook a
> 2164 VCA to the - input, make the trannie a pnp (a la 2N3906), and this will
> feed the Iabc pin of LM13700 quite happily.  Simulations suggest virtually
> perfect equivalence between the input and output currents.
> 
> (I read about this in Horowitz and Hill many moons ago, but managed to
> forget all about it.)

If you look around you will discover this being used over and over again.

> The 2164 Expo Triangle-Core VCO is back in business!!

I told you so... :)

Cheers,
Magnus