[sdiy] Multiplexed Expo Converter?

[Tom Wiltshire]

On 3 Aug 2009, at 20:33, 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?

No, it's *de*multiplexing that's done on the output side of the expo  
convertor. The DAC signal is multiplexed, and passes through the expo  
convertor like that. It's then demultiplexed to give you back the  
multiple signals it represents. That way you only need one expo  
convertor with expensive matched transistors, not lots. It's a very  
neat idea.

T.