[sdiy] Sigma-Delta DAC schematic?

[Grant Richter]

I found the information in EDN magazine. The Sigma-Delta "analog to analog"
converter is the technique. If you consider feeding "fake" data to the
output converter, you can synthesizer different functions.

http://www.e-insite.net/ednmag/archives/1995/042795/09df3.htm

Enjoy!
> 
> This is what I was thinking about. An arbitrary function generator just
> generates an arbitrary voltage "wiggle". Perhaps there are cheap, low parts
> count circuits that would generate interesting sets of "wiggles" also.
> 
> A pseudo random shift register outputs a serial bit string. Depending on the
> length of the shift register, it will repeat in some number of clock cycles.
> 
> So if you had a neat and smooth way to turn the serial bit string into
> analog levels, you could make an LFO with different kinds of repeating
> "wiggles" instead of the more traditional waveforms.
> 
> If you have access to all the bits in the shift register, you could just
> hang a parallel DAC on it, but a DAC that took a 1 bit input would be ideal,
> because the PSSR outputs a serial 1 bit string.
> 
> Most random source designs deliberately avoid repetition, but in this case
> we are looking for it.
> 
> I was also thinking about "parsing" a bit string in different ways. For
> example, a 24 bit serial A/D converter output could be parsed as 12 * 2 bit
> values or 8 * 3 bit values etc., so a static input voltage could point to
> different patterns or shapes of "wiggles".
> 
> Just musing on new CV generators...