[sdiy] Digital accumulator VCO core?

cheater cheater cheater00social at gmail.com
Wed Feb 10 09:13:08 CET 2021


isn't that spread spectrum modulation? the thing we all saw in BIOS
back in the day?

On Tue, Feb 9, 2021 at 8:21 PM Richie Burnett
<rburnett at richieburnett.co.uk> wrote:
>
> > FPGA-based approaches mentioned earlier allow very high sample rates
> that reduce aliases into the noise floor. There are a number of newer
> FPGAs like the Lattice ice40 series that are inexpensive and can easily
> hit multi-MHz sample rates...
>
> It's also possible to add a miniscule amount of pitch dither to the tone
> you're synthesising so that those naive sawtooth harmonics up in the MHz
> around the sample rate don't alias back down to the baseband with an
> annoying discrete line spectrum.  Only a tiny amount of pitch modulation is
> necessary to broaden the spectrum of such very high order harmonics so that
> they all blend nicely together into the noise floor when they alias back
> down below 20kHz.
>
> -Richie.
>
>
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