[sdiy] Digital accumulator VCO core?

Brian Willoughby brianw at audiobanshee.com
Fri Feb 12 06:41:30 CET 2021

On Feb 11, 2021, at 19:22, cheater cheater wrote:
> I hope that when talking about the plan of replacing a single
> capacitor with an adc and a microcontroller, when people suggest
> improving this design by adding a capacitor, the humor isn't lost on
> them.

Well, it is you who started chasing his own tail, so you get what you ask for. :)

> Anyways, an adc by design measures charge, and a lot of the effort
> behind adc design goes into making it appear like it's not measuring
> charge, but to instead make it look like it's measuring voltage or
> current. It must be natural for there to exist an adc architecture
> that measures charge directly - so what is it?

No, an ADC by design measures voltage, using a comparator.

There are perhaps dozens of different ways to perform ADC - successive approximation, flash conversion, delta-sigma - but I can't recall any that work directly on current.

I'm gonna drag you screaming back to the courtroom and ask for a citation here ... again.

If someone can point out an analog to digital conversion circuit topology based on current, I'd be very curious to see it.

You might be thinking of DAC architectures. There are some DAC designs that directly produce current, and that poses a problem. Some include an internal current to voltage converter, but sometimes that has more issues than the DAC itself, and some DAC designs might work better without the I-to-V stage. I've designed at least one product with a super-fast 125 MHz DAC (only 14-bit, though) with differential current output.

Brian Willoughby

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