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Hi all IEEE P802.3ap Task Force
Members,
I have been concerned for IEEEE
802.3 ap Task Force for a long time, and have read through all the
relevant materials available from the website up to now. I do hope I have
a chance to discuss with all members about the project as a system
backplane designer, to share what I think about it. Since it is
inconvenient for us to take part in the face to face meeting and teleconference,
I hope I can use the "e-mail reflector" as a platform to share with you all.
The following is what I want to know
and what I care about most:
1) From the object
objective, the project will cover 1 G per lane, 3.125 GbpsX4
lanes and 10Gbps per lane. Does this mean the channel will meet
all the scope at the same time ?
For the legacy backplane used for
around 1 Gpbs , most of them is made of common FR4 and general
connector,such as 2mm connector without shield pin. I think it is very
hard to upgrade to serial 10 Gbps, at most up to 3.125 Gbps,
economically.
For the legacy backplane used for
around 3.125Gbps per channel, we still use common FR4, not improved
FR4, and apply common manufacturing technology.
For the NRZ coding 10Gbps
application, if we use this kind for backplane, I think this is very hard
to realize. Thus I think for serial 10G backplane, we may using Greenfield
backplane, not legacy backplane.
According to our simulation and
measurement results, the insertion loss of channel up to 3 GHz or so, is
mainly effected by attenuation of copper loss and dielectric, impedance
discontinuity caused by trace and connector, beyond 3 GHz, the via
stub play a more and more important role, firstly, backplane via stub,
secondly, line card stub.
Given we want each layer
in PCB can be routed high speed signals,for NRZ coding 5/6 G
application, backplane via maybe need be backdirlled, for NRZ
coding 10 G application, line card via maybe backdrilled
also.
Does this project plan to using
common PCB technology to make the backplane and linecard ? or using backdirlling
and other technologies to reduce the via stub ?
2) As
for the channel model, I think the channel specifications from TP1 to
TP5 is important, especially for 10G serial application. for 1G per lane and
3.125G X 4 lanes application, maybe we can ignore the influence
caused by the component from TP4 to TP5 (two line card vias and a
compactor), since before 3G Hz, the via's influence is
limited, however, for 10G serial application, especially for NRZ
coding, line card vias also play a great role for the channel performance.
According to our simulation result, for the via routing in layer 2 (line card is
about 2.5mm thick), beyond 5 GHz, the insertion loss of the via drop's sharply.
We need define specifications from TP1 to TP5, instead of the specification
form TP1 to TP4.
3)
As for the test sample, I think we should define some specifications to
guide how to design. The test samples must actually reflect the real
product design, or else, the measurement result and
conclusion according to the result is meaningless. For example,
different types of test launches we used
will greatly influence our test result. I think the rules is, the design will
reflect the practical design, not just for test. For instance, we can use
optimized SMT sma and with a PTH (plated through hole) with 8/10 mil
diameter to reflect the BGA via in practice.
4) As for the channel
crosstalk, some member have mentioned using power sum to define the
spec, however, the project is aim at high speed digital application, all the
standards are defined as voltage in practice, such as eye height,
imput sensitivity, ect. We usually using voltage sum to calculate the worst
case of crosstalk, not power sum.
5)As for the Serdes, It's
better to integrated ac compactor into Serdes, which will significantly
improve the channels performance, for we can reduce 2 line card vias and a
compactor in linecard. Serdes for 10G serial
applications must have adaptive equalization and BIST
function.
Any comments will be
welcomed.
Thanks and Best
regards.
Jia Gongxian
Huawei Technologies Co.,Ltd. Shenzhen China
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