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I have a few comments on the jitter draft you had attached. While
I did not attend the conference call this week, I did discuss this with
my colleague, Juergen Rahn. My comments concern the entire draft,
though I can see that the receiver portion was
already there (you indicated you had written up the transmitter part).
I do plan to attend the meeting next week.
1) Golden PLL, Golden receiver, and receive eqiupment in transmitter
test, referred to in Figure 52-3 and lines 4-15 (approximately) on
p. 357 (just above section 52.8.2). I believe it is appropriate to
specify this equipment, as this defines how
the transmitter measurement is to be made. If, as indicated in
the note beginning on line 9 of p. 357, these are outside the scope of
the document, then it will be difficult to achieve interoperability.
This could happen if 2 different vendors used
different test equipment for transmitter and reciever, respectively,
one of which forced a greater burden on the system under
test than the other. In addition, it would be difficult to verify
compliance if the developer/vendor of equipment used one set of
test equipment and the customer used another.
Regarding the golden PLL, this is in essence equivalent to the high-pass
jitter measurement filter. Its bandwidth should should be equal to
the breakpoint on the sinusoidal jitter tolerance mask. I don't know
if the sinusoidal tolerance mask has been decided on yet; however, using
as examples the ones that have been discussed in the past, the breakpoint
would be 4 MHz for the ITU (SONET/SDH) mask (which has flat level of 0.15
UIpp sinusoidal jitter that must be tolerated) and 6 MHz for the Fibre
Channel mask (which has flat level of 0.1 UIpp sinusoidal jitter that must
be tolerated. The sinusoidal jitter tolerance mask is effectively
a requirement on the minimum bandwidth of the receiver (For example, if
the Fibre Channel mask is used,
it says the reciever must have a minimum BW of 6 MHz if it just tolerates
0.1 UIpp sinusoidal jitter for higher frequencies; if one wants to use
a 4 MHz BW, the tolerance must be increased to 0.15 UIpp for frequencies
above this). By choosing the golden
PLL BW to correspond to this jitter tolerance mask breakpoint, this
ensures compatibility of the transmitter and receiver.
Also in the paragraph on the golden PLL (lines 4 - 7 on p. 357), it
is mentioned that there will be sufficient wander or drift
in the system under test to result in eye closure. If the intent
is to really talk about wander here, then this effect is unimportant.
Wander is low-frequency variation in the bit timing (zero crossings
of the bit slopes). This is well below the bandwidth of the golden
PLL (or of a receiver used in practice) and is easily tracked. However,
it does say that the frequency draft will occur over the time it takes
for the optical signal to traverse the fiber. If this time is sufficiently
short (I don't know what this time is),
then this frequency change would actually be jitter. Since it
is occurring in the transmitter clock of the system under test, I would
classify it as part of jitter generation. What is most important
in determining whether this is jitter or wander is the time scale over
which this occurs compared to the golden PLL time constant (1/BW).
2) For the receiver conformance test (Section 52.8.2), I see that this
is the same as what is in the D2.1 and D2.2 drafts. My main comment
here is that there needs to be consistency between this, the transmitter
test, and the receive sensitivity measurements given in Section 52.8.8
and the tables referenced there (Tables 52-6,7, 10,11, 14,15). Related
to this, it would be useful if a power penalty were specified for the sinusoidal
jitter component in item 8) at the bottom of page 357 (Section 52.8.2);
the usual penalty for this is 1 dB optical. On the consistency issue,
Tables 52-7, 11, and 15 indicate that stressed receive senstivity is measured
with 1e-12 BER at the eye center. They do refer, however, to Section
52.8.11 (in D2.1, which
is 52.8.2 in your document), which has the DDJ, DCD, and sinusoidal
jitter added. In any case, my main point is that
if we define stressed receive sensitivity to include a set of impairments
with a certain power budget at 1e-12 BER with sampling
at the eye center, then if we add the effect of jitter, the BER will
go up. Or, to put it differently, if the BER is 1e-12 with all the
jitter sources present, then it would be much lower if we remove these
sources but keep all the other impairments and the same
power level. If the sinusoidal jitter has a specified power penalty,
then this can be included in the budget. In addition, it means that
sinusoidal jitter tolerance can be measured by measuring the jitter associated
with this power penalty.
Thanks.
Regards,
Geoff Garner
Jonathan Thatcher wrote:
Here is my humble attempt at writing up the transmit side of the jitter specs for clause 52.\As you can see, there are a number of places where help is needed.Will join the PMD serial teleconference at about 15 to 20 minutes after the start.I wrote this based on a version of 52 that was somewhere between 2.0 and 2.1. Sorry if there is any confusion because of this.jonathanJonathan Thatcher
Principal Engineer, World Wide Packets
Chair, IEEE P802.3ae Task Force
Office: 509.242.9228 Fax: 509.242.9001
jonathan@wwp.com
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