[sdiy] Digital accumulator VCO core?

Eric Brombaugh ebrombaugh at gmail.com
Tue Feb 9 21:23:05 CET 2021


Interesting idea. The trouble is that there are a few downsides to
typical modern FPGAs that make them hard to integrate as a pre-
programmed drop-in parts. Most FPGAs require some sort of external non-
volatile configuration memory, plus multiple supply voltages, clock
oscillators and are typically only available in SMT packages.

The particular Lattice parts I've been using lately do have on-chip NV
memory so they could be delivered pre-programmed, but they require 3.3V
and 1.8V supplies and come only in BGA or QFN packages. For most DIY
folks that means an assembled DIP module would probably be most user-
friendly.

One other downside is that it's difficult to do an accurate 12-bit ADC
using only resources on most FPGAs. I have done lower resolution ADCs
using PWM and comparators, but they're pretty slow and noisy so the
control voltage input for a digital oscillator would need an external
accuate ADC for best results.

Overall, a pre-engineered FPGA solution can be done, but there would be
some trade-offs.

Eric

On Tue, 2021-02-09 at 14:11 -0500, Aaron B. wrote:
> 
> I would absolutely buy FPGAs preprogrammed as sawtooth-only DCOs
> like this, and build analog waveshapers around them. Sounds like a
> good
> compromise across sound quality, tracking/temperature stability,
> parts
> count, and ease of tuning.
> 




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