[ibis-macro] Re: Question about clocked Rx AMI models

From: Walter Katz <wkatz@xxxxxxxxxxxxx>
To: "Arpad_Muranyi@xxxxxxxxxx" <Arpad_Muranyi@xxxxxxxxxx>, "ibis-macro@xxxxxxxxxxxxx" <ibis-macro@xxxxxxxxxxxxx>
Date: Mon, 27 Jun 2022 20:43:19 +0000

Arpad,

I believe the original intent of "None" is that the Rx would run in two modes,
one that was clocked, and one with an internal CDR. When "None" the internal
CDR is used.

In DDR5 channels there is a significant lag between the DQ and DQS signal at
the latch because of the DQS distribution inside of the chip. Sinusoidal jitter
becomes a significant impairment, and can be handled with clock forwarding Rx
models. But it is just an impairment, an internal CDR is equivalent to the
controller training the DQ/DQS skew. Memory and controller vendors are both
creating models that use an internal CDR. DDR5 Rx models that support the clock
forwarding will continue to want to use these internal CDR's.

Walter

Walter Katz
Work  508.647-7633
Cell      720.417-3762
wkatz@xxxxxxxxxxxxx
[Description: Description: Visit MathWorks.com]

From: ibis-macro-bounce@xxxxxxxxxxxxx <ibis-macro-bounce@xxxxxxxxxxxxx> On
Behalf Of Muranyi, Arpad
Sent: Monday, June 27, 2022 1:39 PM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Question about clocked Rx AMI models

Hello,

I would like to ask a question about clocked Rx AMI models, when the
Rx_Use_Clock_Input parameter is set to "None".  On pg. 253 the spec
states the following:

"If "None" is selected, then the content of clock_times will be ignored by the
model."

I would like to find out what we mean by "ignored" here.  Let's say the
Rx contains a DFE.  We all know that a DFE needs something to trigger it.
Does "ignore" mean that the Rx model will trigger its DFE on its own,
perhaps with an internal CDR, or does it mean that in the absence of a
clock input, the DFE will be basically idling (not doing anything)?

Now extend the question to an Rx model that has a CTLE.  We know that
CTLE doesn't need clocking, so it could run regardless of what this parameter
is set to, even if it is "None".  What does this mean?  Will CTLE be on all
the time, even if the DFE may get turned off depending on the value of
this parameter?

I wonder whether we should "tighten" this ambiguity in the spec and
establish some rules about this.  Should the specification say, for example,
that when this parameter is set to "None", any equalization in the Rx shall
be turned off?

Thanks,

Arpad
=================================================================

References:
- [ibis-macro] Question about clocked Rx AMI models
  - From: Muranyi, Arpad

[ibis-macro] Re: Question about clocked Rx AMI models

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