Re: [BP] Informative Channel
Hello, all,
As silicon designer point of view, RX input level is very sensitive
issue. If it is too low, we have to install pre-amp, DC offset
chancellor, etc. and they consume more power and silicon area.
Let's try simplified consideration;
..01010101.. signal somewhere PRBS consists of 5GHz sine wave
(and small 3rd harmonics...). Pre-emphasis should be set most strong
level, the other word it should be full swing 1Vppd typ at TX side.
In a case of equation 69.2 per draft 0.91, -25.3dB at 5GHz,
..01010101.. signal of 1Vppd TX makes 54mVppd or 27mVpp single-ended.
However
1. TX minimum amplitude is spec'ed 0.8Vppd, so any RX should receive
the signal from the TX (effective -2dB).
2. Return loss max is 5dB at equation 72-2 per draft 0.91. The
mismatch makes 1~2dB signal level loss at each of TX-channel and
channel-RX. Let's assume total -3dB min.
3. Frequency ripple may be allowed -5dB min at 5GHz in the discussion
on Jun 1.
Assumption of above 3 effects are -10dB min !!
Then the really worst case of eye height at RX input will be 18mVppd
or 9mVpp single-ended by ..01010101.. signal !!
It doesn't include crosstalks, noise and jitter.
Should RX designers really consider such small level ??
Another values;
Figure 72A-2 in draft 0.91 shows -28.86dB "typical" ISI loss at
5.156GHz. When we use the number, RX input will be 28.8mVppd or
14.4mVpp single-ended from 1Vppd TX.
If we add above 3 effects, it will be 9.6mVppd or 4.8mVpp single-
ended.
If we consider maximum ISI loss rather than "typical",
Ooooom...
Anyway these kind of small values of RX input may be smaller than
peaks of noise and crosstalk.
M. Sugawara
NEC Electronics America
> John, all:
>
>
>
> Yes I think I can run them.
>
>
>
> You're right. I actually did understand the presentation
>but didn't remember where the red line was. Using the
>
>presented values we still get only about 17 mV pp single-ended. I'm
>concerned that this is too small.
>
>
>
> Steve A.
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>
>________________________________
>
>From: DAmbrosia, John F [mailto:john.dambrosia@tycoelectronics.com]
>Sent: Thursday, June 02, 2005 6:41 AM
>To: steve.anderson; STDS-802-3-BLADE@listserv.ieee.org
>Subject: RE: [BP] Informative Channel
>
>
>
>Stevei,
>
>I agree with your comment regarding using one set of simulations, which
>is why I brought it up on the phone call in my presentation. I would
>feel better if we did have another perspective. Can you run the
>channels exactly as Joe as with all of the variations he did, and then
>we can see what the tool says as well.
>
>
>
>Your comments regarding the LMS fit are incorrect, so let's go through
>it.
>
>
>
>1. The insertion loss data is the raw data. Let's consider KR. First
>the insertion loss data must be above the blue line called out in Rich's
>presentation.
>
>2. An LMS fit is then done on the data. This becomes the attenuation of
>the channel, and must be greater than / above the worst case attenuation
>limit, i.e. equation 69.2 per draft 0.9 or the famous Goergen equation.
>At 5 GHz this equation is at -25.3 dB.
>
>3. Based on the LMS fit we then look at the ripple on the insertion
>loss, i.e. the raw data. It has to fit the concept illustrated on Page
>9 of Rich's presentation, which is Fig 69.4 per Draft 0.9
>
>
>
>All of these conditions must be met. It looks to me like you are
>using the blue line as being where the LMS fit needs to be above, which
>is approximately -30 at 5 GHz.
>
>
>
>Hopefully this clarifies the situation.
>
>
>
>John
>
>
>
>
>
>-----Original Message-----
>From: owner-stds-802-3-blade@ieee.org
>[mailto:owner-stds-802-3-blade@ieee.org] On Behalf Of Steve Anderson
>Sent: Wednesday, June 01, 2005 11:02 PM
>To: STDS-802-3-BLADE@listserv.ieee.org
>Subject: [BP] Informative Channel
>
>
>
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> All,
>
>
>
> At today's meeting it seemed like much of the informative
>channel spec is being based on just one
>
>set of simulations / analyses - those done by Joe Abler of IBM. Other
>analyses - including stat eye -- have not been
>
>as optimistic. In particular, when significant amounts of Tx and Rx
>jitter are included, the number of channels
>
>that "work" drops considerably.
>
>
>
>In anderson_01_1104 I showed that I could get stat eye results that were
>better (more optimistic) than
>
>Joe Abler's for a small subset of channels, provided that I used
>assumptions similar to his. When I use other
>
>assumptions that I feel are reasonable, I get results that are worse
>than Joe's. It seems that small differences
>
>in assumptions can lead to dramatically different results. (This
>probably doesn't surprise anyone!)
>
>
>
>One can argue about which set of assumptions should be used. But this
>probably cannot be resolved,
>
>since it is partly dependent on the implementation of the receiver, the
>IC packaging, etc. A spectrum of chip
>
>implementations will lead to a spectrum of results.
>
>
>
>This leads to my first question: Shouldn't the informative channel be
>based on analyses
>
>that are at the pessimistic end of the spectrum?
>
>
>
> Another question: The LMS line in Richard's presentation
>could lie right on the attenuation limit. This
>
>is about -30 dB at 5 GHz. Richard purposely didn't include any package
>effects. But I'm going to assume that
>
>these can add another 2 dB of attenuation. With a Tx level of 800 mV
>ppd this gives us 20 mV ppd at the
>
>receiver, or 10 mV pp single-ended. Do other chip people think we can
>receive this?
>
>
>
> Regards,
>
>
>
> Steve A.