[sdiy] How does a DCO work?

[Richard Wentk]

At 10:24 30/12/2004, Paul Maddox wrote:
>Richard,
>
> > There's an even more complicated answer for an all-digital environment
> > which includes the detailed workings of phase accumulators and bandwidth
> > limiting to prevent aliasing, but that's probably more than you want or
> > need to know at this point.
>
>:-)
>You don't need to worry about bandlimiting Phase accumulator based
>oscillators. as they are effectivly variable sample rate based. Its only
>things with a fixed sample rate (DSPs for example) that bandlimiting becomes
>an issue.

Are you sure? Or alternatively, are we talking about the same thing?

You can implement a phase accumulator with a fixed sample rate, in which 
case you get aliasing just as you would in any other fixed sample rate 
system. See e.g.

http://ifmaxp1.ifm.uni-hamburg.de/PAPER_ROW2001_1.PDF

for one example. (Page 3)

Obviously if your counter free-runs from a variable clock rate, that counts 
as a variable sample rate system, and in that case you're right.

But they are different implementations, with different properties.

Richard