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

  • From: Todd Westerhoff <twesterh@xxxxxxxxxx>
  • To: "Arpad_Muranyi@xxxxxxxxxx" <Arpad_Muranyi@xxxxxxxxxx>
  • Date: Wed, 12 Dec 2012 16:56:09 -0500 (EST)

Arpad,

We have a published spec that says the analog model is to be included in the 
calculation of that channel impulse response.

Anything else is not compliant.

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
 
 
“I want to live like that"
                                             -Sidewalk Prophets
 

On Dec 12, 2012, at 4:21 PM, "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx> wrote:

> Todd,
>  
> This is not super-theoretical-science in the clouds.
>  
> It can be done just as practically and “easily” as the
> EQ, DFE and CDR AMI algorithms can be done in the DLL-s.
> It involves the same kind of algorithm knowledge, and
> programming skill.
>  
> The question is, do we want to let model makers to do
> this, and possibly get a bunch of bad models from
> inexperienced people, or should we, the EDA vendors
> still have the opportunity to sell our expertise and
> provide higher quality and more reliable solutions to
> our customers and AMI model users.
>  
> Thanks,
>  
> Arpad
> ==========================================================
>  
> From: ibis-macro-bounce@xxxxxxxxxxxxx 
> [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Todd Westerhoff
> Sent: Wednesday, December 12, 2012 2:54 PM
> To: Dmitriev-Zdorov, Vladimir; 'Gregory R Edlund'
> Cc: ibis-macro@xxxxxxxxxxxxx
> Subject: [ibis-macro] Re: Analog Buffer Model Inside DLL
>  
> 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
> 
> 
> 
> <image001.gif>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>
> 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
>  
>  
> “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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