[sdiy] current mirror for NPN expo?

[Lanterman, Aaron]

I think the best way to think of the expo converter is only one of the transistors is really doing the expo conversion; all the rest are temperature-compensating current mirrors. 

- Aaron

On Sep 19, 2011, at 12:42 PM, dan snazelle wrote:

> ok let me try that
> 
> i had the base going to the CV input instead of the ground
> 
> On Sep 19, 2011, at 12:39 PM, Lanterman, Aaron wrote:
> 
>> 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
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>