[sdiy] Multiplexed Expo Converter?

[Dave Manley]

Ingo Debus wrote:
> 
> Am 03.08.2009 um 05:06 schrieb David G. Dixon:
> 
>> Oh, I get it!  The multiplexing is on the input side of the EC (the CVs),
>> not the output side.  My bad!
> 
> Hm, as I understand it, a muxed expo converter is used in a polyphonic 
> synth; with one expo converter driving several VCOs. So the signal flow is:
> Voice assigner (DAC) -> expo converter -> mux -> S&H (several) -> linear 
> VCO (several).
> 
> So the multiplexing is done on the output side of the expo converter, no?

Is this really done?  Most implementations I've looked at have:

DAC -> multiple (addressable) S&H -> vc_thing

The most common expo is a voltage to *current* conversion (for a VCO, 
with the current controlling the charge rate of the timing cap, or for a 
VCF, the OTA control current).  The chain you describe would have the 
expo output a voltage.  What products do this?  A typical example for 
what I'm describing is the Prophet-5.

-D