[sdiy] Generating a large number of CV outputs

[Roman Sowa]

I'm triggered, because that's something I was recently evaluating (but 
don't feel like doing for various reasons).
The DACs can be as cheap as they wish, but will never be S&H-MUX cheap.
Surely there are cheap excellent 12-bit DACs now with price per channel 
below $1 but that's still a lot of money. You could also consider 
96-channel DAC and just don't bother designing huge circuitry around it, 
but not only it cost $80 in singles but also is huge BGA monster.

I reckon you're not doing it for space or military, so IMHO the mux way 
is the only way still.

With 100 outs at "few" kHz update rate you're struggling with 1us analog 
MUX settling time, and when you say 16-bit, that makes me shiver.
What you can do is split it to couple of separate muxes with their own 
DACs, and feed them sequentially. Huge analog circuitry with lots of 
muxes, opamps, caps and countless meters of traces will be happier 
getting an update every 10us rather than 1us. Interlace DAC update 
moments with MUX address changes to make sure new output is well settled 
before MUX opens.
Also, with multiple DACs and MUXes you can spread the circuitry on the 
board so DAC's opamp will not have to drive too much, but only a couple 
of MUXes gathered around it.

OTOH I would love to see someone doing 100-outs MUX with single DAC 
spitting 16-bit precision at 1Msps

Roman


W dniu 2023-12-08 o 01:35, Danjel van Tijn / intellijel pisze:
> What is the current ideal way to generate a large number of CV outputs 
> from a single CPU?
> 
> Let's say I wanted to generate 100 outputs with an update rate of a few 
> kHz and an equivalent bit depth of 12 or 16 bits.
> 
> I know that back in the day when DACs were extremely expensive, the 
> designs would use a single DAC and then demux to a bunch of S&Hs.
> 
> Now that DACs are cheaper, is it better to chain a bunch of 8- or 
> 16-channel DACs?
> 
> Or would it make more sense to use an FPGA and create a giant 
> multi-channel 1-Bit DAC?
> 
> Looking at some Elektron hardware teardowns it appears that they are 
> using the latter approach.
> 
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