RE: [IBIS] RE: [IBIS-Users] Query reg. USB1.1 IBIS model generation

Vivek,
 
You might want to check with your EDA vendor.  IBIS 1.1 is old, and not
compatible with later versions of IBIS (especially 3.2 and 4.x).
Consequently, support for some features might not function as expected.
 
Lynne
 
 
"IBIS training when you need it, where you need it."
 
Dr. Lynne Green
Green Streak Programs
http://www.greenstreakprograms.com
425-788-0412
lgreen22@mindspring.com


  _____  

From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of Muranyi,
Arpad
Sent: Tuesday, January 22, 2008 10:11 AM
To: ibis-users@eda.org; ibis@eda.org
Subject: RE: [IBIS] RE: [IBIS-Users] Query reg. USB1.1 IBIS model generation


Vivek,
 
Generally, legacy IBIS is not able to describe buffers which
have feedback.  You can, however, describe any behavior with
the *-AMS extensions in IBIS.  On the other hand, if you are
lucky, you may still be able to make a model using legacy
IBIS features if you know exactly what your buffer does and
you know how IBIS models work.  This may require some trial
and error, and I am not in a position to guide you through
this.
 
Regarding the 45 Ohm R_fixture question, you will get the best
correlation when R_fixture equals the T-line impedance.  The
model will still work well if the T-line has a different
impedance, but the farther you go away the less accuracy you
can expect.  Give it a try...
 
Arpad
----------------------------------------------------------------

  _____  

From: Vivek kumar Singh [mailto:Vivekkumar.Singh@arm.com] 
Sent: Monday, January 21, 2008 11:27 PM
To: Muranyi, Arpad; ibis-users@eda.org; ibis@eda.org
Subject: RE: [IBIS] RE: [IBIS-Users] Query reg. USB1.1 IBIS model generation



Hi Arpad,

     For both low and high speed usb, I generated IBIS models with R_fixture
of 50 Ohms. 

 

Mine is USB1.1.  I then did correlation with spice model. Full speed was
matching, but Low speed is not matching with spice.

 

2 queries I have :

   1) In Low speed design, I have slew correcting feedback capacitors. So,
while generating IBIS should I take care of it separately or IBIS will
handle it? 

   

   2) For USB1.1, 45 Ohm R_fixture is used. So, while validating should I
use TLINE also of 45 Ohm? What changes should I make?

 

Regards,

Vivek

 


  _____  


From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of Muranyi,
Arpad
Sent: Monday, January 21, 2008 10:07 PM
To: ibis-users@eda.org; ibis@eda.org
Subject: [IBIS] RE: [IBIS-Users] Query reg. USB1.1 IBIS model generation

 

Vivek,

 

R_fixture has nothing to do with the 1.5k or 15k resistors.

Select a value for R_fixture that matches the transmission

line impedance.  In the USB case it would be 45 Ohms (single

ended) if my memory serves me right.

 

I would also suggest that you look at the IBIS Cookbook for

help.  There are a lot of good ideas in there.

 

http://www.vhdl.org/pub/ibis/cookbook/cookbook-v4.pdf

 

Arpad

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

 


  _____  


From: owner-ibis-users@server.eda.org
[mailto:owner-ibis-users@server.eda.org] On Behalf Of Vivek kumar Singh
Sent: Sunday, January 20, 2008 10:34 PM
To: ibis-users@server.eda.org; ibis@server.eda.org
Cc: Vijaya kumar Vinukonda
Subject: [IBIS-Users] Query reg. USB1.1 IBIS model generation

Hi All,

    I'm having problem with ibis model generation for USB1.1 . 

I have following 3 queries :

 

since USB operates in Upstream and Downstream applications with pullup and
pulldown resistors 1.5k and 15k Ohm respectively. Will it have any effect on
choosing R_fixture value for IBIS VT data generation ????

 

What actually we take the value of R_fixture for USB1.1 ?

 

Can someone elaborate on setup for Ibis model generation for USB1.1.

 

 

Regards,

Vivek

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