Re: gEDA-user: Difficulty in border areas

[Magnus Danielson <cfmd@xxxxxxxxxxxx>]

From: Daniel Nilsson <daniel@xxxxxxxxxxxxxxx>
Subject: Re: gEDA-user: Difficulty in border areas
Date: Thu, 6 Jan 2005 19:57:58 -0500
Message-ID: <20050107005758.GB22097@xxxxxxxxxxxxxxxxxxxx>

> > d) What if I want to make 44.1kHz from say 33MHz and need it
> > super-hyper-roxx0r stable because am using it for feeding Hi-Fi audio DAC and
> > even the tiniest jitter would be audible?  How do I do it with PLL?
> 
> Sorry, don't know much about audio design... I do know that all PLL
> circuits will have jitter though, there is no such think as a zero
> jitter PLL that I've ever heard of.

Zero-jitter does simply not exist. You can have sufficiently low jitter, but
that is another thing. Zero-jitter oscillators/PLLs is really like the holy
grail, everyone wants them but they just can't be found.

Now, assuming you have a low jitter oscillator of the right frequency, then you
either divide down the reference frequency, the output frequency or both to
create the input signals to the phase comparator. The output of the phase
comparator is then filtered through a loop filter and that gives you the
control voltage to the oscillator. A good phase comparator, a good loop gain
and loop filter gets you the right benefits of the long term stability from the
reference and the short term stability of the oscillator. It's just a little
magical touch in choosing the phase comparator and loop filter parameters.
There's books on this. The best book isn't the book by Best, but it is still
lot of valuable information in there.

Besides, most A/D and D/As run off from higher frequencies as I recall it.

Cheers,
Magnus