regarding noise introduced by PLL:


What really happens here is you get some jitter in the clock. That means=20
that although the frequency of the clock over a short period of time (a few=
=20
cycles or so) is accurate the individual cycles of the clock may vary=20
slightly in length.

In other words, given a program that toggles an output quickly you might=20
notice a bit of 'fuzz' on the rising and falling edges of the signal on an=
=20
oscilloscope. This is caused by the clock jitter which is, more or less,=20
unavoidable with a PLL.

In a funny way clock jitter can help you pass EMI testing. This is because=
=20
the spectrum of the clock frequency and its multiples is 'spread' due to th=
e=20
instantaneous variations in the clock.

-- Bob Ammerman
RAm Systems

--=20
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