[sdiy] Generating a large number of CV outputs

[Mike Bryant]

  *   https://northcoastsynthesis.com/news/dacs-and-bit-count/
et seq

I just had a read of this and generally very well put.  However you seem to miss out mentioning PDM  between the sections on PWM and Delta-Sigma.  This gives faster settling time of DC voltages than PWM, as well as other advantages when producing audio as its easier to push the noise out of band.

I used PDM (using 74LS TTL and some transistors) in the 1980s for an accurate fast settling DC voltage reference in a HP instrument requiring better then 16 bits as one of its uses was to verify in production the then new 16 bit(-ish) convertors.

________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Matthew Skala via Synth-diy <synth-diy at synth-diy.org>
Sent: 08 December 2023 01:21
To: Danjel van Tijn / intellijel <danjel at intellijel.com>
Cc: SDIY <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Generating a large number of CV outputs

On Thu, 7 Dec 2023, Danjel van Tijn / intellijel wrote:

> 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.

Which is it, 12 or 16?  You've got your work cut out for you if you really
want 16-bit absolute DC voltage precision on even one output.  The number
of outputs isn't your biggest concern when that's a serious goal.

> 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?

Using an FPGA is going to require you to solve for yourself a lot of
problems that would be solved for you if you used ready-made DAC chips.
I wouldn't be eager to do that.  I also don't think 1-bit DACs are
well-suited to generating precise DC voltages; as I wrote at length in my
recent Web log series (https://northcoastsynthesis.com/news/dacs-and-bit-count/
et seq.), they reproduce signals, not voltages.

However, if you do put in the effort to make it work, the FPGA would
probably be cheaper.

--
Matthew Skala
North Coast Synthesis Ltd.
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