[sdiy] Digital accumulator VCO core?

cheater cheater cheater00social at gmail.com
Thu Feb 11 08:46:38 CET 2021

Here's one thing I've been wondering about. Is there a form of ADC
where every sample represents the total charge that passed through a
conductor since the last sample? Normally, an ADC will only sample
voltage (or current) at the time of sampling, but we don't really know
anything about what happened between sampling intervals. If we assume
that the current was roughly constant during the sampling, that's
fine. But if it changed during that time, then we have to do some sort
of interpolation. Even if we do a linear interpolation, maybe the
current going through the conductor was concave or convex. Being able
to sample the total charge going through a cap would be much easier,
since I'd be converting the input data into a charge amount anyways
(to be added to the virtual capacitor).

On Tue, Feb 9, 2021 at 4:43 AM cheater cheater
<cheater00social at gmail.com> wrote:
> Hi all,
> I was wondering if anyone ever experimented with replacing the
> accumulator core with a digital setup. Essentially you would have
> control voltage turned into current being shunted to ground, and you'd
> sample this current with the ADC, accumulating it in software. A
> 16-bit, 12 MS/s ADC like the Cirrus Logic WM8196SCDS/V costs only ~$2
> - $3 depending on how many you need, and my guess is that this would
> be more than enough bit depth and sampling rate to preclude numerical
> error. I think this would be able to do FM at audio rate. So does
> anyone do this sort of thing?
> The nice thing is you don't need to use solid state switches any more,
> your switchover is immediate, so no tracking error due to that. Also
> perfect for complex wave shapes, you could have a VCO like that easily
> output a waveform from a wavetable while still being fully capable of
> FM.
> You might want to use a shunt resistor with bad tempco ... just to
> keep things feeling "analog" ...

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