RE: [IBIS-Users] RE: [IBIS] input signal for model usage

From: Muniswara Reddy Vorugu <Muniswarareddy.Vorugu_at_.....>
Date: Tue Mar 17 2009 - 21:09:37 PDT
Hi Fabio,

                As wang said, IBIS models has a limitation of producing
I/O behavior at higher clock frequencies.

                you could be hitting this max limit way less than what
you can achieve, because of improper modeling of the V-T tables. 

 

                Some of the potential problem are

                                1: large lead time( initial stable time)

                                2: Large final dead time ( stable)

                

Some simulator can handle this  situation.

I have observed that Buffer element in HSPICE-2008 and later versions
can handle this situation.

If your tool cannot handle it.   You can modify VT tables as discussed
in the file attached.

There is one more discussion on the same point, you can find it on the
IBIS quality specifications webpage.

 

My  suggest is ( go one by one)

1: Cut down all unwanted dead time.

2: You  can try cutting down  same amount of LEAD time  from all V-T
tables( both Rising and falling), better if it is same for all corners.

3:  if you want to still more improvement, You can have different lead
time for different corners.  

     This can result in VT waveforms looking weird ( all corners
waveform overlapping ), but make a note of the cause in NOTE field .

( NOTE : if you get required improvement at any of the stage stop there.
Because in each stage you move a step way from conventional) 

 

This can help you in attaining maximum possible frequency of operation.

 

Thanks,

Muniswar

 

 

 

 

 

 

 

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of Lance Wang
Sent: Wednesday, March 18, 2009 1:35 AM
To: ibis-users@eda.org; ibis@eda.org
Subject: RE: [IBIS-Users] RE: [IBIS] input signal for model usage

 

Fabio,

 

There is another situation could be for the second point.

 

Sometimes, when you compare the waveforms from Spice transistor-level
simulations or measurements and waveforms that from the IBIS model
simulations, you will find the differences. It could be happened that
you are using faster input clock frequency. The reason is that IBIS
model has the limitations or say your IBIS simulator has the
limitations. 

 

So Arpad is right, you can not fix it for recapturing the VT curves. But
sometimes it doesn't mean you buffer can not handle this kind of clock
frequency. It could be just the limitations of your IBIS model or
simulators.

 

Regards,

 

Lance Wang

978-764-2298

IO Methodology Inc.

 

________________________________

From: owner-ibis-users@server.eda.org
[mailto:owner-ibis-users@server.eda.org] On Behalf Of Muranyi, Arpad
Sent: Tuesday, March 17, 2009 12:16 PM
To: ibis-users@server.eda.org; ibis@server.eda.org
Subject: RE: [IBIS-Users] RE: [IBIS] input signal for model usage

 

Fabio,

 

You are correct on the first one, and almost correct

on the second.

 

1)  The edge rate of the stimulus to an IBIS model will

not change its output edge rate, but it will shift it,

depending on how the tool implements the threshold on

the stimulus input of the IBIS model.  This is not related

to the IBIS Vinh and Vinl (or related) parameters.  The

IBIS specification doesn't say anything about how the

threshold of the input stimulus should be detected by 

the IBIS model implementation.

 

2)  If you clock the IBIS model faster than the V-t curve

can handle it you would need to make a new model, but not

only a new model, but also a new chip.  The fact that a

V-t curve goes only so fast indicates that the chip itself

can't go faster.  So no matter how hard you try to make a

new set of V-t curves, you won't succeed unless you redesign

the chip itself...

 

Arpad

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

 

________________________________

From: owner-ibis@server.eda.org [mailto:owner-ibis@server.eda.org] On
Behalf Of Fabio BRINA
Sent: Tuesday, March 17, 2009 8:00 AM
To: 'Muniswara Reddy Vorugu'; ibis-users@server.eda.org;
ibis@server.eda.org
Subject: RE: [IBIS-Users] RE: [IBIS] input signal for model usage

 

Thank you Muniswar,

 

 could you confirm (or correct) these propositions? :

 

 - if I change only rise/fall slew at the input (A_in as you say)

   the Output response is the same. (could be only a little shift time
in the Output?)

 

 - if I change the input clock frequency (fck), the Output response is
correct

   until fck is under the frequency used in the V-T tables generation.

   (if I want to use an higher clock frequency, I have to generate a new
model

    with differents V-T tables)

 

 are that right?

 

 many thanks,

 

 Fabio

 

 

 

________________________________

From: owner-ibis-users@server.eda.org
[mailto:owner-ibis-users@server.eda.org] On Behalf Of Muniswara Reddy
Vorugu
Sent: Tuesday, March 17, 2009 12:00 PM
To: Fabio BRINA; ibis-users@server.eda.org; ibis@server.eda.org
Subject: [IBIS-Users] RE: [IBIS] input signal for model usage

Hi,

The OUTPUT of I/O ( IBIS model)  does not depend on the Rise/Fall slew
at the input of I/O ( say A_in ).

 

If you mean. Can you have different  LOW/HIGH duration? 

You can give different clock/pulse frequency, but there is an upper
limit of the clock.

The upper limit of the clock frequency is limited by the duration of the
V-T tables/Ramp time.

 

Thanks,

Muniswar

 

From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of Fabio
BRINA
Sent: Tuesday, March 17, 2009 3:55 PM
To: ibis-users@eda.org; ibis@eda.org
Subject: [IBIS] input signal for model usage

 

Hello IBIS experts, 

 

 Once an IBIS model has been created, can be used in different Input
speeds?

 

 In other words: if I consider an I/O model, Can I use every input Pulse
with

 several rise/fall time Or I have to use only the same pulse used in the


 model creations?

 

I hope is clear what I mean.

 

Thanks,

Fabio

 

 


-- 
This message has been scanned for viruses and 
dangerous content by MailScanner <http://www.mailscanner.info/> , and is

believed to be clean. 

 

-- 
IMPORTANT NOTICE: The contents of this email and any attachments are
confidential and may also be privileged. If you are not the intended
recipient, please notify the sender immediately and do not disclose the
contents to any other person, use it for any purpose, or store or copy
the information in any medium. Thank you. 
-- 
This message has been scanned for viruses and 
dangerous content by MailScanner <http://www.mailscanner.info/> , and is

believed to be clean. 
-- 
This message has been scanned for viruses and 
dangerous content by MailScanner <http://www.mailscanner.info/> , and is

believed to be clean. 


-- 
This message has been scanned for viruses and 
dangerous content by MailScanner <http://www.mailscanner.info/> , and is

believed to be clean. 
-- 
This message has been scanned for viruses and 
dangerous content by MailScanner <http://www.mailscanner.info/> , and is

believed to be clean. 

-- 
IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium.  Thank you.

-- 
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.



--------------------------------------------------------------------
|For help or to subscribe/unsubscribe, e-mail majordomo@eda-stds.org
|with the appropriate command message(s) in the body:
|
|  help
|  subscribe   ibis       <optional e-mail address, if different>
|  subscribe   ibis-users <optional e-mail address, if different>
|  unsubscribe ibis       <optional e-mail address, if different>
|  unsubscribe ibis-users <optional e-mail address, if different>
|
|or e-mail a request to ibis-request@eda-stds.org.
|
|IBIS reflector archives exist under:
|
|  http://www.eda-stds.org/pub/ibis/email_archive/ Recent
|  http://www.eda-stds.org/pub/ibis/users_archive/ Recent
|  http://www.eda-stds.org/pub/ibis/email/         E-mail since 1993
Received on Tue Mar 17 21:12:45 2009

This archive was generated by hypermail 2.1.8 : Tue Mar 17 2009 - 21:13:29 PDT