[sdiy] current mirror for NPN expo?

[Lanterman, Aaron]

On Sep 19, 2011, at 12:15 PM, David G Dixon wrote:

>> can anyone point me towards info on how to use ONE NPN EXPO 
>> to drive two vcos?
> 
> Can't you just mirror the current-sourcing one?  I.e., tie its emitter to
> the other two, and connect its base to the other current-sourcing one?  You
> should be able to replicate the current as many times as you want this way.
> I did it with five transistors in a four-pole filter once; it worked a
> treat.

I think this is an example, courtesy Jurgen and Rene:

http://www.uni-bonn.de/%7Euzs159/rs2040.png

Well, it's a VCF and not a VCO, but I think the expo converter illustrates David's idea.

- Aaron