Ali,
I believe the meeting will be too late. If you have a proposal, or
something in mind, can you at least email it?
I think what we have with slight mods works great. But that's just me.
-joel
Ali Ghiasi wrote:
Adam
I have just start looking at this problem more carefully, I don't have
a specific proposal right now but
I will bring one for the next interim meeting. Thanks for clarifying
the issue.
Ali
Healey, Adam B (Adam) wrote:
Message
Ali,
Thanks Ali, I think I better understand your
concern now.
As I recall, the return loss equation was simply
the 10GBASE-CX4 return loss equation (a -12dB plateau from 0.4 to 2GHz)
extended to 15GHz and was a fairly arbitary placeholder. Channel data
presented to the task force has shown that this is an unrealistic
expectation of the channel and must be corrected. I believe that Joel
has identified this as a work item for the channel model ad hoc and
given the volume of channel data presented from multiple parties, I
believe it is one that we can close.
Do you have a specific proposal for the return
loss mask?
Best Regards,
-Adam
Adam
Please see my comments below in red.
Healey, Adam B (Adam) wrote:
Hi Ali,
I do agree with TP-1 and TP-4 definition.
They are located at the "component edge" of the
transmitter and receiver respectively. The definition of "component
edge" includes any external termination components required by the
transmitter/receiver and the AC-coupling capacitors, when used.
This implies that the backplane connectors (and
mezzanine connector, when used) are part of the "channel"
specification. Channel return loss requirements would need to be
satisfied looking into the channel at either TP1 or TP4. Transmitter
return loss requirements would be defined looking into TP1. Receiver
return requirements would be defined looking into TP4.
Channel return loss, based on the conventions
that we are using, will likely be dominated by the first mated
connector as you point out.
To include the interaction between the
transmitter/receiver and the channel, a cascaded system model is
required. This can be accomplished a variety a ways (cascaded
T-parameters for example, refer to OIF). I suspect that this is
something the signaling ad hoc will need to address. The charter of
the channel model ad hoc, like the cabling ad hocs 802.3 has had in the
past, is to define the channel return loss looking into TP1 and TP4. I
use the word "channel" rather than backplane, as it now should be clear
the our definition of TP1 and TP4 is not only the backplane but the
trace on the node/hub (line, daughter, whatever naming convention you
prefer) cards as well.
I apologize if you already understood this. Of
course, you may not agree with the above methodology, which is
fine. Let's discuss it on the reflector. It sounds like you are
advocating that we define the backplane connector, which is something I
think we have been trying to avoid. Please clarify.
Adam, I was not advocating specifying a
backplane connector and looks like based on the the definition
of goergen_03_0704
you already have connector as part of the channel. The part I am
puzzled is the return loss
associated with current channel model "-14 dB up to 15 GHz". Based on
my data and experience specifying such
low return loss is not practical unless you introduce significant loss
on the daughter-board. With 14 dB return loss at
TP1/TP4 toward the channel you are practically ignoring the most
significant effect "double reflection between the connector and the
IC"!
Thanks,
Ali
Thank you,
-Adam
Joel
Joel Goergen wrote:
Ali,
We have been focusing on this for several months now. I think Steve
has presented nothing new that hasn't been published and, at a min,
agreed to in some form of straw poll.
I am not disagreeing that these were
agreed in the straw poll, I just didn't participated in some
of earlier meeting.
I would like to offer a thought ...
For the channel ... we use the SMA and SMA foot print that allows for a
clean launch. At both ends of the channel. This allows us to see the
SDD11/SDD22 without doing a major de-embedding and still allow for freq
to 12.5Ghz.
How can you define a channel
"backplane"
but not define a minimum attribute for the connector.
There is no reason to de-embed the connector as the connector is part
of the channel. A compliant
channel must meet an specified transmission and reflection property
which include connector.
For the tp1 and tp4 ... we then let the tx (tp1) handle the BGA and
via, the rx(tp4) handle the via, both cap pads, both via and BGA pad.
It will be easier to do the de-embedding and specify the SDD11/SDD22 as
seen by the chip from the channel.
The methodology specified currently in
BP
is suitable for chip to chip applications but not for backplane.
Where do you handle connector effect and multiple reflection between
the connector-IC? In 4Gig FC we addressed some of these issues and do
specify the channel which include the connector.
Thanks,
Ali
Just my own thoughts .....
-joel
Ali Ghiasi wrote:
Steve
Looking at your channel model, I see the return loss up to 15 GHz is
better than 12 dB.
How do you get -12 dB return loss at 15 GHz with connectors, what kind
of connector
are you assuming? The most challenging effect are the primary
reflection between
silicon and the connector at this speed.
Thanks,
Ali
Stephen D. Anderson wrote:
All:
I updated the synthesized S-parameter files that I presented in
Portland. The new revision provides a much better NEXT file. The Thru
file was also improved so that SDD11 magnitude has ripples. You may
recall that the previous SDD11 magnitude was flat over most frequencies
of interest and that this was viewed as unrealistic.
These are intended to match the NEXT and Thru templates that we have
thus far agreed on.
If you see anything blatantly wrong with the files, please let me
know.
Regards,
Steve A.
|