[time-nuts] Frequency Stability of Trimble Mini-T
SAIDJACK at aol.com
SAIDJACK at aol.com
Thu Oct 16 23:57:11 UTC 2008
Hi Hal,
>First, we understand metastability. We can measure it and predict it. It
it
>mattered, we could test each individual part.
That was exactly my original point. The discussion got off topic, I just
wanted to point out that it is a matter of probability, and the math to
calculate this probability of failure is well known and understood.
The math says that you cannot prevent a metastable event, even if there are
1000 flip flops. The probability is never zero. And since the processes are
stochastic, the first failure could happen within 2 seconds of power on, even
with 10000, or a million cascaded flip flops. You can never prevent a
metastable event going through all of the flops. You can just make that probability
approach zero. Actually, if you had a million cascaded flip flops one of them
would probably fail due to other reliability reasons :)
>Second, the failure mode is exponential in a parameter we can control. So
>given a particular set of parts to pick from, it's reasonable to make a
>design with a probability of error small enough so that other things are
much
>more important.
Right! My original point again. The question was: how often do crystal jumps
happen. How often do metastable events happen. Both may be just a matter of
statistics and probability.
If we don't see a crystal jump within say one month of operation, we can
probably say the probability of one happening is extremely low.
But I have seen jumps happen after 3 months of continuous, documented
operation without any jumps, so again we may never have certainty that
jumps/metastable events will not happen. We just have to make them happen so seldomly
that they won't matter to the application at hand. But again if it jumps after 3
months, no one can guarantee it won't jump after 10 minutes.
bye,
Said
____________________________________
From: SAIDJACK
To: SAIDJACK
Sent: 10/16/2008 16:43:33 Pacific Daylight Time
Subj: Fwd: [time-nuts] Frequency Stability of Trimble Mini-T
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