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

  • From: "Todd Westerhoff" <twesterh@xxxxxxxxxx>
  • To: "'Dmitriev-Zdorov, Vladimir'" <vladimir_dmitriev-zdorov@xxxxxxxxxx>, "'Gregory R Edlund'" <gedlund@xxxxxxxxxx>
  • Date: Wed, 12 Dec 2012 15:54:25 -0500 (EST)

Vladimir,



Not clear to me how you propose to handle the reflections associated with 
discontinuities at the point where the TX and RX analog circuits interface 
to the channel.  More importantly, even if it’s theoretically possible, that 
doesn’t make it practical.



I’ll admit I’m guessing here, but I expect Greg wants to solve a problem, 
not just establish that it should be possible to solve it.



Todd.

Todd Westerhoff

VP, Software Products

Signal Integrity Software Inc. • www.sisoft.com

6 Clock Tower Place • Suite 250 • Maynard, MA 01754

(978) 461-0449 x24  •  twesterh@xxxxxxxxxx



“I want to live like that”

                                             -Sidewalk Prophets



From: Dmitriev-Zdorov, Vladimir [mailto:vladimir_dmitriev-zdorov@xxxxxxxxxx]
Sent: Wednesday, December 12, 2012 2:39 PM
To: twesterh@xxxxxxxxxx; 'Gregory R Edlund'
Cc: ibis-macro@xxxxxxxxxxxxx
Subject: RE: [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] On Behalf Of Todd Westerhoff
Sent: Wednesday, December 12, 2012 11:51 AM
To: 'Gregory R Edlund'
Cc: 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

6 Clock Tower Place • Suite 250 • Maynard, MA 01754

(978) 461-0449 x24  •  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
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



Inactive hide details for Todd Westerhoff ---12/12/2012 12:31:11 PM---Greg, 
That is not possible. The analog model, by definitiTodd 
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>
To: Gregory R Edlund/Rochester/IBM@IBMUS
Cc: "ibis-macro@xxxxxxxxxxxxx" <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
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> 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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