17 Nov
2011
17 Nov
'11
5:26 p.m.
On Nov 17, 2011, at 5:55 PM, Eric Smith wrote:
The reason people say that's a no-no is that it
doesn't do as good a job at reducing the probability of metastability. However, the
probability of metastability with a clock of frequency f with opposite-phase FFs is
exactly the same as the probability with conventional same-phase FFs at a frequency of 2f
(provided that the FF characteristics are otherwise identical), so if you do analysis for
2f and get acceptable results, you can use frequency f with opposite phases.
Yes, but that's precisely what most people miss (which is why they tell you not to do
it; they're guarding against stupid). As long as you actually know what the
implications are and accept them, it's fine (as with so many things that are
"no-nos" in engineering).
- Dave