Re: [10GBASE-CX4] comments on latest CX4 revision

[Mike Jenkins <jenkins@lsil.com>]

Dan,

I share Clark's concerns.  The only related presentation I found for February (cx4_electrical_specs_02_18_03_Raleigh.pdf) showed simulations, not hardware.

• These simulations used up all the space in the template, passing only when the pre-emphasis was adjusted a couple percent (which is easy to do in simulations, but tough, slow and expensive in silicon).
• The need to change the pre-emphasis was due to modelling 2 inches of PCB.  What if it's 3 inches instead?  or a different dielectric?  or a different package?
• Assumptions in this simulation included perfect impedance matching and no reflections.  I very much doubt that a GigaCN-to-SMA adapter board would meet those assumptions.
• No tolerance is allowed for jitter or amplitude noise.
• Margin for amplitude noise is 10% max, including ringing & reflections.
• Depending on how you model it, slow risetimes (0.41 UI) either just make it or just miss with everything else perfect.

Apologies if I've missed a presentation with actual hardware compared to
this template.  But if we're proceeding without any hardware experience,
I am frankly concerned that this approach will be a measurement nigntmare.

Regards,
Mike

"DOVE,DANIEL J (HP-Roseville,ex1)" wrote:

Hi Clark,

I believe a lot of your questions would have been addressed
at our meetings. We have had numerous presentations with
measurements of cable assemblies and devices where the first
thing that is done, is determine the impact of the connectors
and PC board, and other impairments on the measurement.

Nobody is claiming this is easy, that is not required. It is
necessary to ensure compliance that we have a transmitter that
meets an objective template, and a channel that meets a set of
objective specs, and a receiver that works when connected to
the two former items. Verification is required, but those of
us who have been working on this have spent a substantial
amount of time doing just that.

The reason we spec'ed TP2 at the back side of the mated
interface was specifically so that we could get a physical
point as a reference plane.

Regards,

Dan

-----Original Message-----
From: Clark Foley [mailto:clarkf@mxim.com]
Sent: Thursday, February 27, 2003 10:30 AM
To: 'ddprocurve@antelecom.net'; 'stds-802-3-10GBCX4@ieee.org'
Subject: RE: [10GBASE-CX4] comments on latest CX4 revision

Dan,

Has such a correction for impairments been demonstrated at 3.125Gb/s?

Clark

On Wednesday, February 26, 2003 10:11 PM, ddprocurve@antelecom.net
[SMTP:ddprocurve@antelecom.net] wrote:
>
> Hi Clark,
>
> We discussed this and the conclusion was that there will be some
impairment
> caused by the fixturing (loss, etc) but that must be calibrated out by the
> user. We did not want to get into mandating how much loss, what kind of
> SMAs, etc. Rather, we spec the signal at the interface and rely upon the
> user to be able to make that measurement.
>
> This is consistent with 1000BASE-T and other 802.3 technologies where the
> measurement requires some calibration by the user to compensate for probe
> effects.
>
> Dan
> >
> >
> >54.7.3.6 Differential Output Template and Figure 54-3
> >The interconnect from the MDI to the scope for measuring against this
> >template has not been adequately described.  I could not find any
> >information on the plumbing.  A tight template like this one must be
> spec'd
> >along with the interconnect hardware.
> >
> >Please consider readily available adapters and cables for this.  I
suggest
>
> >that the test interface be comprised of a 1m, 24AWG cable to connect
> >between the MDI and a GigaCN-to-SMA adapter board.  If you don't have one

> >of these boards yet, you will soon!  From the SMA to the scope, we can
use
>
> >short, high quality cable.  This is easy and convenient.
> >
> >
> >Regards,
> >Clark Foley
> >Maxim Integrated Products
> >(503) 547-2018
> >
> >

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