EMRFD Message Archive 559

Message Date From Subject
559 2007-03-23 14:49:46 Mike Brainard Phase Noise of Frequency Dividers
What do we know about the phase noise contribution of frequency
dividers made with TTL (say 74F or 74AS) versus similar dividers made
with CMOS (say 74HC or 74AC)? If there is a difference, at what
performance level does it become important?

560 2007-03-23 17:04:30 Luiz Amaral Re: Phase Noise of Frequency Dividers
In my experience with frequency synthesizers, the importance level of
dividers is much smaller than the VCO, varactor and phase comparator noise
levels. I have seen (for common designs) that after diminishing the VCO
noise to a minimum, it appears that the second in importance is the varactor
that must be chosen carefully. The phase comparator noise is difficult to
diminish because it contains inherently the noise of the two types, VCO and
reference types. So, it is really difficult do measure consistently the
dependence of the noise on the divider technology. One important thing is
that output spurs (not white noise) are more difficult to be wiped out when
the CI's peak currents are higher, as the TTL case.

Luiz - PY1LL

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