[sdiy] Generating a large number of CV outputs

[Neil Johnson]

Hi,

Jonatan Liljedahl wrote:
> One way to reduce the noise coming from the MUX control signals is to use grey code instead of binary count, so that only one adress line changes at a time.

Yes that can reduce the amplitude of the spike at the clock frequency,
but I suspect what Mike is referring to is what is termed "spread
spectrum" which spreads the RF energy across a band rather than all in
one place.  We do that on large SoC memory buses and you can see on a
spectrum analyser when it is turned on (looks like "__.........__")
and off (looks like "_____/\_____").  It's usually a setting in the
memory bus controller.

Anyway, PDM ... yeah, a lot of tiny MEMS mics use it now.  And you can
do stereo on a single data line too (L on rising edge, R on falling
edge).

And CVs: having a "mother of all CV sources" can work if you're
careful.  When you're dealing with that many CVs then the
cost-per-channel becomes significant due to the multiplying effect: in
a 100-channel design adding 1c per channel adds $1 to the BOM.  A
decent DAC, 4051s, C0G caps and decent JFET opamps is very cheap in
quantity.

Neil