[ibis-macro] Re: Analog Buffer Model Inside DLL

  • From: <fangyi_rao@xxxxxxxxxxx>
  • To: <vladimir_dmitriev-zdorov@xxxxxxxxxx>, <twesterh@xxxxxxxxxx>, <gedlund@xxxxxxxxxx>
  • Date: Thu, 13 Dec 2012 12:28:06 -0700

Hi, Dmitriev;

Please see my answers in brown.

But, on the other hand, can such resolution be made without letting the model 
know about something about the channel.

For parameters that depend on channel characteristics, DLL can resolve them in 
AMI_Init.

Do you think that this hypothetical function should also take non-equalized 
channel response as an input?

No. One of the intentions of this new API is to determine analog model 
parameters in the anticipation of advanced analog model like the one proposed 
in BIRD 116 being accepted. If the analog model is fixed, then everything can 
be resolved in AMI_Init.

Regards,
Fangyi

From: fangyi_rao@xxxxxxxxxxx<mailto:fangyi_rao@xxxxxxxxxxx> 
[mailto:fangyi_rao@xxxxxxxxxxx]
Sent: Wednesday, December 12, 2012 8:40 PM
To: Dmitriev-Zdorov, Vladimir; twesterh@xxxxxxxxxx<mailto:twesterh@xxxxxxxxxx>; 
gedlund@xxxxxxxxxx<mailto:gedlund@xxxxxxxxxx>
Cc: ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>
Subject: RE: [ibis-macro] Re: Analog Buffer Model Inside DLL

What is the termination of each port of the combined s-parameter? S-parameter 
alone doesn’t sufficiently describe the analog circuit. We still need to know 
the termination to calculate impulse response, unless we assume it’s infinite 
(based on the statement that analog/DLL interface has high impedance).

On a separate note, please don’t forget crosstalk. If there are N interfering 
differential channels, we need a 4N-port S-parameter. The AMI DLL pretty much 
needs to run a SPICE simulator to combine the analog model into the s4Np.

Fangyi

From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx> 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Dmitriev-Zdorov, Vladimir
Sent: Wednesday, December 12, 2012 11:39 AM
To: twesterh@xxxxxxxxxx<mailto:twesterh@xxxxxxxxxx>; 'Gregory R Edlund'
Cc: ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>
Subject: [ibis-macro] Re: Analog Buffer Model Inside DLL

In an abstract/theoretical way, it is still possible that AMI DLL correctly 
takes care of the “impulse response” by adding its internal model to it. Then 
however it should not be an ‘impulse response’, but 2- or 4-port S-parameters 
representing the core portion of the channel, which does not include analog 
models. Each model then can ‘append’ its analog part to the S-parameters, and 
restore the resulting impulse response, if needed for equalization. Instead of 
returning the updated impulse response, the Init function (or how we call it) 
will return the updated touchstone file, which then is passed to the Rx model, 
with the same purpose.

The objection here is that Tx must have the complete channel info, with Rx 
analog model,  before its Init function can start thinking about equalization, 
but then ‘appending’ analog models could be either separated from Init, and 
organized as one more function, possibly combined with what Fangyi proposed 
about resolving dependences, or we could still do everything in just one 
function, but perform a few cycles of Initialization, for example: (Tx_Init(), 
Rx_Init()), (Tx_Init(), Rx_Init()) … which resembles “backchannel” 
communication on Init() stage.

Of course, the writer of the AMI model must be able to do some operations with 
touchstone files, such as appending the model to it, and converting it into 
transfer function, finding impulse response by IFFT, etc.

From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx> 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Todd Westerhoff
Sent: Wednesday, December 12, 2012 11:51 AM
To: 'Gregory R Edlund'
Cc: ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>
Subject: [ibis-macro] Re: Analog Buffer Model Inside DLL

Greg,

Ask yourself how the person writing an algorithmic model should accurately 
model the reflections associated with an unspecified channel.  If there’s a way 
to do that, I’d like to hear about it.

Todd.

Todd Westerhoff
VP, Software Products
Signal Integrity Software Inc. • www.sisoft.com<http://www.sisoft.com>
6 Clock Tower Place • Suite 250 • Maynard, MA 01754
(978) 461-0449 x24  •  twesterh@xxxxxxxxxx<mailto:twesterh@xxxxxxxxxx>

“I want to live like that”
                                             -Sidewalk Prophets

From: Gregory R Edlund [mailto:gedlund@xxxxxxxxxx]
Sent: Wednesday, December 12, 2012 1:41 PM
To: Todd Westerhoff
Cc: ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>
Subject: Re: [ibis-macro] Analog Buffer Model Inside DLL


Todd,

Thanks for the response.

So, there are no "mathematical tricks" one can play in the DLL to account for 
the absence of the analog buffer model in the impulse response?  You can tell I 
haven't taken enough time to think this through all the way.  I'm having a 
knee-jerk reaction to a discussion that's going on internally.  8-)  I'm about 
to dig into the IBIS 5.1 flow material to support my position.  I just wanted 
to make sure I had my ducks in a row and get some outside corroboration.

Anyone else care to chime in?

Greg Edlund
Senior Engineer
Signal Integrity and System Timing
IBM Systems & Technology Group
3605 Hwy. 52 N  Bldg 050-3
Rochester, MN 55901



[cid:image001.gif@01CDD923.75733660]Todd Westerhoff ---12/12/2012 12:31:11 
PM---Greg, That is not possible. The analog model, by definition, interacts 
with the channel and must be

From: Todd Westerhoff <twesterh@xxxxxxxxxx<mailto:twesterh@xxxxxxxxxx>>
To: Gregory R Edlund/Rochester/IBM@IBMUS
Cc: "ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>" 
<ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>>
Date: 12/12/2012 12:31 PM
Subject: Re: [ibis-macro] Analog Buffer Model Inside DLL

________________________________



Greg,

That is not possible. The analog model, by definition, interacts with the 
channel and must be included in the impulse response. The equalization, also by 
definition, is considered to be electrically isolated from the channel and is 
thus represented in the DLL.

Putting the analog model in the DLL violates a fundamental assumption of 
IBIS-AMI. You may get good-looking results, but they will be invalid.

Todd.


--

Todd Westerhoff
VP, Software Products
SiSoft
6 Clock Tower Place, Suite 250
Maynard, MA 01754
(978) 461-0449 x24
twesterh@xxxxxxxxxx<mailto:twesterh@xxxxxxxxxx>
www.sisoft.com<http://www.sisoft.com/>


“I want to live like that"
                                             -Sidewalk Prophets


On Dec 12, 2012, at 1:13 PM, Gregory R Edlund 
<gedlund@xxxxxxxxxx<mailto:gedlund@xxxxxxxxxx>> wrote:

What nasty things are likely to happen if someone puts the analog buffer model 
inside the DLL?  At the very least, the impulse response will be incorrect.

Are there any circumstances under which this can work correctly?

Greg Edlund
Senior Engineer
Signal Integrity and System Timing
IBM Systems & Technology Group
3605 Hwy. 52 N  Bldg 050-3
Rochester, MN 55901

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