Walter,
What you proposed is basically Variant 2 we discussed at ATM meetings back in
Jan. Back then the ATM group compared Variants 1 and 2 and decided to combine
these two into Variant 3, based on which BIRD 210 was written.
Comparison between Variants 1 and 2 was documented in the following ATM link.
http://ibis.org/atm_wip/archive/20210120/fangyirao/AMI%20Redriver%20Flow/AMI_redriver_flow_2021_v0.pdf
Fangyi
From: ibis-macro-bounce@xxxxxxxxxxxxx <ibis-macro-bounce@xxxxxxxxxxxxx> On
Behalf Of Walter Katz
Sent: Monday, March 08, 2021 6:06 AM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Redriver Flow - I totally agree that the flow in Fangyi's
BIRD 210 is correct, it just does not need two additional columns in the
Impulse Matrix or a new reserved parameter
CAUTION: This message originates from an external sender.
All,
The statistical redriver flow in BIRD 210 specifies that the impulse response
input to each AMI_Init is the cumulative impulse response of everything
upstream, and that the output contains the models equalization applied to that
input impulse response. This is correct. There is no need to add a column to
the impulse response to do this, just use column 1.
The handling of crosstalk needs to be done by the EDA tool. It needs to find
the impulse response of all paths of the connection from all Tx to it’s Rx, and
to the Rx’s it aggressors. All the EDA tool needs to do this is the
equalization of all of the models between the primary Tx (included) and the
terminal Rx (excluded). The equalization of all models (except the terminal Rx)
is determined by initialing the second column in the Impulse Matrix to a Unit
Impulse Response. The output of the second column of the Impulse Matrix is the
impulse response of the equalization of that model. The “aggressors” argument
of these calls to AMI_Init will be 1. The Impulse Matrix input to the terminal
Rx will have “aggressors” equal to the actual number of Tx aggressors to this
Rx. The terminal Rx will apply the “LTI” equalization (generally the
equalization before the Rx DFE) to these aggressor impulse response columns.
All legacy models support this flow. Models that are not terminal Rx already
apply their equalization to all of the columns of the Impulse Matrix, and
terminal Rx apply just the LTI part of their equalization to the aggressor
columns. There is no need for a reserved AMI parameter that says this, and
certainly no need to add additional columns beyond the number of “aggressors”.
We have seen one Tx model in the past 12 years that optimized its FFE taps
based on the impulse response of the downstream channel. This feature was never
used because it over-equalized the channel and gave overall poorer results.
Thus the need for back channel which is addressing this.
I am OK if IBIS decides it needs a new parameter to support this flow, and
document this flow by replacing the flow in column 1 and indicating that
“aggressors” can include columns that the EDA adds to extract the impulse
response of model. But lets keep the number of columns in the impulse matrix =
aggressors+1.
Walter
Walter Katz
Work 508.647-7633
Cell 720.417-3762
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