RE: Let's get started
Regarding the question:
"What do you think are the most important features of a jitter test
pattern?"
This is what I remember from a variety of meetings plus a couple of my own:
1. Relatively short in length (can be loaded into BERT memory).
2. Has nearly 50% transition density (+/- tolerance TBD).
3. Contains long run lengths
3a. Longest length (TBD)
3b. Rapid trends towards large disparity (TBD).
4. Stresses the PLL clock recovery (TBD). Combinations of:
4a. Long run lengths
4b. Phase transitions
4c. Polarity biased transitions (some PLLs only look at rising or falling
edges)
5. Able to create very short patterns for some optical tests (e.g. OMA or
E/R).
6. Able to run in loop back (need independent Tx and Rx pattern generators)
7. Able to count "down" to BER rate of TBD. (10e-3?)
8. Able to reset counter
9. If two counter registers are required (depends on the TBD in # 7 above),
one must be slave to the other (slave register loaded when the master is
read, only).
10. Able to synchronize in presence of bit errors (BER TBD).
11. Pattern flexibility.
12. Technique works for both the WAN and LAN phy (WAN must include the A1/A2
sequence; LAN must not).
13. TBDs are based on an probability of occurrence equal to once per day for
single bit errors.
14. Stressful, but reasonable, for EMI testing (e.g. no short patterns; see
#1 above).
I would like to note that number 5 above was not shown in the Ewen/Thatcher
presentations in March due to information overload. This is simply
accomplished by turning on and holding on the seed reload active. Easy.
I think that I mentioned in my talk that number 10 could potentially be
accomplished by use of the error rate counters.... If not, that is one way
to define and potentially select the synchronization BER.
I would like to note here that I feel very strongly about # 11. I would
definitely write a TR against the draft if we did not do this. I have zero
(yep, read that 0) confidence that we will select the ideal pattern(s) in
the next six months. In short, I believe there is a very high probability
that some (or all) of the TBDs above will change as we get experience in the
field. We definitely have history supporting this.
Number 14 is not strictly required since this could be done with real data.
But, as many of us have already learned on the test field, EMI measurement
is already a difficult to repeat exercise. It is nice to remove as many of
the random variables as possible. This is, therefore, not required. But, it
would be nice.
jonathan