[ibis-macro] Re: What part of Legacy IBIS is used by IBIS-AMI

  • From: "Walter Katz" <wkatz@xxxxxxxxxx>
  • To: <DBanas@xxxxxxxxxx>, <Arpad_Muranyi@xxxxxxxxxx>, "'IBIS-ATM'" <ibis-macro@xxxxxxxxxxxxx>
  • Date: Wed, 18 Jul 2012 13:01:22 -0400 (EDT)

David, Arpad, Dan,

 

The approach that Dan and David want to take makes the LTI assumption, and
that the AMI_Init function does not change its equalization based on the
impulse response input. In this case the channel can be solved by
convolving the IR of the Tx, Rx, and channel in any order. Under these
assumptions the IR input to the Tx and/or Rx AMI init function can be a
Dirac-Delta function. Technically, this is not 0,1,0,0,. but 0,1e9,0,0, .
if the time step is 1e-9.

 

Walter

 

From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of David Banas
Sent: Wednesday, July 18, 2012 12:52 PM
To: 'Arpad_Muranyi@xxxxxxxxxx'; 'IBIS-ATM'
Subject: [ibis-macro] Re: What part of Legacy IBIS is used by IBIS-AMI

 

I meant passing in the list of numbers, [0, 1, 0, 0, .], in the
`impulse_matrix' parameter of the `AMI_Init()' function.

-db

 

 

From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Wednesday, July 18, 2012 8:26 AM
To: 'IBIS-ATM'
Subject: [ibis-macro] Re: What part of Legacy IBIS is used by IBIS-AMI

 

Oh I see, you are not trying to analyze the channel, you

are trying to get the model's response and check what

the model itself does.  I am sorry for being slow in

catching up to you, but what do you mean by

 

"a {0, 1, 0, 0, .} sequence"

 

then?  Are you referring to a bit sequence, as in a

digital waveform:

 



 

or a series of dirac delta functions

 



 

multiplied by the pattern of 0 1 0 0?

 

Thanks,

 

Arpad

============================================

 

From: David Banas [mailto:DBanas@xxxxxxxxxx] 
Sent: Tuesday, July 17, 2012 1:17 PM
To: Muranyi, Arpad; 'IBIS-ATM'
Subject: RE: [ibis-macro] Re: What part of Legacy IBIS is used by IBIS-AMI

 

No, I'm definitely referring to the impulse response, because my ultimate
goal is to validate the model's frequency response, and one way to get
that is to take the FFT of its impulse response.

-db

 

 

From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Tuesday, July 17, 2012 11:13 AM
To: 'IBIS-ATM'
Subject: [ibis-macro] Re: What part of Legacy IBIS is used by IBIS-AMI

 

David,

 

Are you perhaps confusing "impulse"

with "pulse" response?  Please

clarify your question.

 

Thanks,

 

Arpad

=====================================

 

From: David Banas [mailto:DBanas@xxxxxxxxxx] 
Sent: Tuesday, July 17, 2012 1:08 PM
To: Muranyi, Arpad; 'IBIS-ATM'
Subject: RE: [ibis-macro] Re: What part of Legacy IBIS is used by IBIS-AMI

 

Arpad,

 

Could you provide some clarification, please?

Are you saying that probing for a model's impulse response, by sending a
{0, 1, 0, 0, .} sequence into the AMI_Init() function is invalid?

(I've been having good results with this technique, and you've got me
worried that those results are invalid.)

Of course, I understand that I may pick up some aliasing, if my sample
rate is insufficient. But, other than that, it is a valid technique for
probing a model's impulse response; isn't it?

 

Thanks,

-db

 

 

From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Tuesday, July 17, 2012 10:40 AM
To: IBIS-ATM
Subject: [ibis-macro] Re: What part of Legacy IBIS is used by IBIS-AMI

 

Dan,

 

There are several issues that need to be considered in this topic.

 

The biggest issue in my mind is the question of time step.  An

ideal step or impulse function has zero width.  In time step based

simulators the best we can do for a step function is a slope that

is one time step wide, and for an impulse function two slopes

(one up and one down) that are a total of two steps wide.  No

matter how small you make your time step, these functions are

never going to be what they should be.  This introduces errors

and the amount of error will depend on the time step, which may

depend on the EDA tool's internal algorithms.

 

Regarding:  "Another way to look at it would be to say that if a model
writer intended for a model to work with an ideal impulse response, they
could essentially ship and IBIS file that pretty much only contains a
c-comp, "zeroed out" V-I tables, and sharp edge rate in the ramp data to
make it a fairly ideal driver."

 

This is basically a suggestion to implement an ideal step or impulse

function generator in the IBIS [Model].  But where is the buffer's

model then?  You would either have to put the buffer's impedance

model in series or in parallel with this function generator.  And the

C_comp would belong to the buffer's model, not the ideal function

generator.  But why would you go this route, when the EDA tool can

do the function generator in the stimulus, and the model maker can

do the model of the device in the IBIS [Model]?

 

Thanks,

 

Arpad

=======================================================================

 

 

 

 

From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Dan Dvorscak
Sent: Tuesday, July 17, 2012 11:49 AM
To: IBIS-ATM
Subject: [ibis-macro] Re: What part of Legacy IBIS is used by IBIS-AMI

 

Hi all,

 

Sorry to reply late to this thread.  I had been keeping an eye out for it,
but seem to have missed it. 

 

Per what Greg and Arpad were discussing, should it not be up to the model
writer to decide whether or not an ideal or an IBIS-generated impulse
response is to be used?  My expectation would be that a given IBIS buffer
that points to an AMI model will contain all of the IBIS analog model
features that the model writer intends to be included in the channel
characterization.  In that sense if a user or EDA tool chooses to ignore
any of those features they are using the model in a way that it was not
characterized for.  

 

Another way to look at it would be to say that if a model writer intended
for a model to work with an ideal impulse response, they could essentially
ship and IBIS file that pretty much only contains a c-comp, "zeroed out"
V-I tables, and sharp edge rate in the ramp data to make it a fairly ideal
driver. 

 

Does that seem like a fair assessment?

 

Thanks,

 

-Dan

 

 

On Wed, Jul 11, 2012 at 10:37 AM, Muranyi, Arpad
<Arpad_Muranyi@xxxxxxxxxx> wrote:

Greg,

 

The IBIS specification is intentionally silent about

how to generate the impulse response for the channel,

because there are different ways to do it, and EDA

vendors might want to use their own "smarts" to do it

the "best" way.

 

You are correct, if someone wants to extract such an

"ideal" IR, you would only make use of the C_comp and

the impedance provided by the I-V curve from the analog

model.

 

BIRD 120 doesn't give any more detail (or restrictions)

on how to generate the impulse response.  So the EDA tool

is free to do it the way they think it is the best to do

it.

 

I hope this helps,

 

Arpad

===========================================================

 

From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Gregory R Edlund
Sent: Wednesday, July 11, 2012 9:15 AM
To: 'IBIS-ATM'; ibis-macro-bounce@xxxxxxxxxxxxx


Subject: [ibis-macro] Re: What part of Legacy IBIS is used by IBIS-AMI

 

What if an EDA programmer wanted to discard the VT and ramp data and
compute an "ideal mathematical" impulse response assuming a delta
function?  Is that allowed by BIRD 120?  I took a quick look and didn't
see anything specific about how to calculate the impulse response.  In the
"ideal mathematical" case, I would think all you need is C_Comp and some
resistance extracted from the IV tables.

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 "Walter Katz" ---07/11/2012 03:53:30 AM---I
agree."Walter Katz" ---07/11/2012 03:53:30 AM---I agree.

From: "Walter Katz" <wkatz@xxxxxxxxxx>
To: <Arpad_Muranyi@xxxxxxxxxx>, "'IBIS-ATM'" <ibis-macro@xxxxxxxxxxxxx>
Date: 07/11/2012 03:53 AM
Subject: [ibis-macro] Re: What part of Legacy IBIS is used by IBIS-AMI
Sent by: ibis-macro-bounce@xxxxxxxxxxxxx

  _____  




I agree.
 
Walter
 
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Tuesday, July 10, 2012 11:44 PM
To: IBIS-ATM
Subject: [ibis-macro] Re: What part of Legacy IBIS is used by IBIS-AMI
 
That is correct.
 
Arpad
================
 
From:  <mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
ibis-macro-bounce@xxxxxxxxxxxxx
<mailto:%5Bmailto:ibis-macro-bounce@xxxxxxxxxxxxx%5D>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Mirmak, Michael
Sent: Tuesday, July 10, 2012 6:07 PM
To: Walter Katz
Cc: IBIS-ATM
Subject: [ibis-macro] Re: What part of Legacy IBIS is used by IBIS-AMI
 
Walter,
 
Thank you!  So, someone using IBIS-AMI models with valid traditional data
in a workflow should expect changes in the IBIS TX C_comp or V-t (or
[Ramp]) data to have an impact on the results provided by the receiver in
an IBIS-AMI-based flow, assuming nothing else changes?
  

-          MM

 
From: Walter Katz  <mailto:%5Bmailto:wkatz@xxxxxxxxxx%5D>
[mailto:wkatz@xxxxxxxxxx] 
Sent: Tuesday, July 10, 2012 12:20 PM
To: Mirmak, Michael
Cc: IBIS-ATM
Subject: What part of Legacy IBIS is used by IBIS-AMI
 
MM,
 
The Legacy part of an IBIS model is used to generate the Impulse Response
of the channel. 
 
One method of generating the impulse response is to do a step response,
and take the derivative of the waveform at the Rx input.
 
A simulator uses a combination of the Tx [Voltage Range], C_Comp, IV, VT
and Ramp data, and the Rx C_Comp and IV data. Of course, [External Model]
can also be used by a simulator.
 
The following required Tx IBIS fields are not used in the AMI flow: 

Vmeas

The following required Rx IBIS fields are not used in the AMI flow: 

Vinl
Vinh

 
Walter
 
 
Walter Katz
wkatz@xxxxxxxxxx
Phone 303.449-2308
Mobile 303.335-6156
 





 

-- 
Daniel Dvorscak
ANSYS, Inc.
67 South Bedford St.
Suite 202E
Burlington, MA 01803
Tel:  781.229.8900 x352
Fax: 781.229.8624

 

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