[sdiy] VCO Linear Voltage

[David G. Dixon]

> >  I think there must be a way to
> >  process the current from 2164 such that it can be fed into any
> >  voltage, but I haven't figured it out yet, and I have a feeling
> >  that it would involve something fairly exotic.
> 
> It only seems exotic until you know what it is called - try "current
> conveyor" in your favourite search engine.  It is also sometimes
> called an "ideal transistor", but that is not the most useful search
> term because different folks have different ideals.

I've had a look at a few references on this device (Sedra and Smith's
original letter, the AN4198 application note, and a paper by Rana and Pal on
opamp realizations), and I don't see that this device is going to hold the
input voltage at anything but the output voltage (-13.5V in the case of
LM13700).  What it will do is change the output impedance to a very high
value (as will the much simpler Howland current source, for example, but
with the same problem of not altering the input voltage).

Am I missing something here?