[sdiy] Digital accumulator VCO core?

Mattias Rickardsson mr at analogue.org
Thu Feb 11 13:47:41 CET 2021


The filter doesn't make the signal constant between samples. It doesn't
even make its slope constant between samples.

What it does do is to average the fastest wiggles in a signal in a way
similar to what you are asking for. :-)

/mr


Den tors 11 feb. 2021 13:41cheater cheater <cheater00social at gmail.com>
skrev:

> This is true in that the anti-aliasing filter limits the bandwidth of
> the signal, making it constant between sampling periods before it gets
> to the ADC. However, that's not the same as sampling the whole charge
> that was transported in the time between the sampling intervals. In
> specific, the anti-aliasing filter will shunt a portion of that charge
> to ground, bypassing the ADC.
>
> On Thu, Feb 11, 2021 at 1:32 PM Mattias Rickardsson <mr at analogue.org>
> wrote:
> >
> > Den tors 11 feb. 2021 08:48cheater cheater <cheater00social at gmail.com>
> skrev:
> >>
> >> 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).
> >
> >
> > This is essentially what an anti-aliasing filter does for you.
> >
> > /mr
> >
>
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