[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> 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]<mailto:[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> 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]<mailto:[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<mailto: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> 
[mailto: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<mailto: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



[cid:[email protected]]"Walter Katz" ---07/11/2012 03:53:30 AM---I 
agree.

From: "Walter Katz" <wkatz@xxxxxxxxxx<mailto:wkatz@xxxxxxxxxx>>
To: <Arpad_Muranyi@xxxxxxxxxx<mailto:Arpad_Muranyi@xxxxxxxxxx>>, "'IBIS-ATM'" 
<ibis-macro@xxxxxxxxxxxxx<mailto: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<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>

________________________________



I agree.

Walter

From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto: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: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx> 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]<mailto:%5Bmailto:ibis-macro-bounce@xxxxxxxxxxxxx%5D>
 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:wkatz@xxxxxxxxxx]<mailto:%5Bmailto:wkatz@xxxxxxxxxx%5D>
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<mailto:wkatz@xxxxxxxxxx>
Phone 303.449-2308<tel:303.449-2308>
Mobile 303.335-6156<tel: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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