Re: [IBIS-Users] Rref_diff keyword

From: Cynthia Low <ibis_user_at_.....>
Date: Tue Jul 07 2009 - 03:55:08 PDT
Hi Bob

Thank you so much for your reply. It was indeed helpful. However, there is something that I was not certain off and hope you can help to clarify. 

In your reply, you mentioned that Rref_diff can be used but to prevent the parser warning message by adding in the Cref,Vref and Rref subparameters.
Which parser checker are you refering to? IBISchecker v4.x.x? Can you please specify?I basically use the latest IBIS checker v4.2.2 to check and there is no warning on the usage.

Also, I will be using this Rref_diff keyword for a dedicated differential output buffer and Cref, Vref and Rref will not exist, (which you suggest to state Cref = 0F ,Vref=1.163 (to follow Vmeas?) and Rref=1E9), this can be applied? It is a dedicated output buffer which do not share any single ended timing test-load information, it could still be use in that way? You can refer back to the previous attachement for the timing test load that I wish to specified (resistor). 

Lastly and most importantly, I noticed that this Rref_diff keyword, which is used in v4.1 IBIS specification is not integreted into many simulation tool yet, and also the ICX checker may not allow this keyword to pass, if so, can this subparameters still be use? How will the simulator tools interprete the Rref_diff keyword. Also, if the simulator is using a v3.2 ibis checker, this keyword will be redundant as it will not pass, am I rite? Could you please kindly comment on this?

Rref_diff and Cref_diff can also be used for [Model]s when
they are connected by the [Diff Pin] keyword without the [External
Model] extension.  However, to prevent parser warning messages,
it is strongly encouraged to still add the Cref and/or Vref and Rref
subparameters.  Cref can be 0 F and/or Rref can be very large.
The parser check was added to be sure that the model maker intentially
meant to have a negligible single-ended timing test load.

Thanks and best regards
Cynthia




________________________________
From: Bob Ross <bob@teraspeed.com>
To: Cynthia Low <ibis_user@yahoo.com>
Cc: ibis-users@server.eda.org; bob@teraspeed.com
Sent: Tuesday, July 7, 2009 1:45:08 PM
Subject: Re: [IBIS-Users] Rref_diff keyword

Hi Cynthia:

My answers are in your text.

Best Regards,
Bob

Cynthia Low wrote:
> Dear IBIS experts
>  I am currently looking at the Rref_diff subparameters under the [model] keyword and the usage of this subparameters. This subparameters is only available in IBIS specification of v4.1 but not in older version. May I know how this subparameters keyword is being used? the detail of the question is as below.
>  IBIS Spec:
> Rref_diff is used for true differential buffer timing test loads. where the buffer hv to be specified only when the [Diff Pin]
> keyword connects two models, and each buffer references the same model.  The Rref_diff and Cref_diff subparameters can be used with the Rref, Cref, and Vref subparameters for a combined differential and signal-ended timing test load.
> 1. My questions will be, can this Rref_diff sub-parameters be used ONLY when we engaged using the true differential [External Model] with either spice or vhdl-ams? As shown in the IBIS spec.

Yes, Rref_diff can be the only timing test load parameter for true
differential buffers, as illustrated in Section 6b.

>  2. Can this Rref_diff keyword be used in the context of a normal true differential buffer under the [Model] keyword, and at the same time the model is define under [Diff Pin] section to describe the timing test loads just like how the rest of the Cref, Vref keyword are used to facilitate for board-level timing simulation, with the setup as attached. Can the Rref_diff keyword used under the example below?

Rref_diff and Cref_diff can also be used for [Model]s when
they are connected by the [Diff Pin] keyword without the [External
Model] extension.  However, to prevent parser warning messages,
it is strongly encouraged to still add the Cref and/or Vref and Rref
subparameters.  Cref can be 0 F and/or Rref can be very large.
The parser check was added to be sure that the model maker intentially
meant to have a negligible single-ended timing test load.

So the example below may produce parser Warning messages.  If that is
the case, I would add

Cref = 0F

and/or possibly

Vref=1.163
Rref=1E9

as needed to remove any Warning messages.

>  [Model] 25_lvds
> Model_type Output
> Polarity Non-Inverting
> Enable Active-Low
> Rref_diff = 100
> Vmeas = 1.163
> C_comp  1.8pF  1.8pF  1.8pF  Please kindly comment. Thanks.
>  Regards
> Cynthia
> 
> 
> -- 


-- Bob Ross
Teraspeed Consulting Group LLC    Teraspeed Labs
121 North River Drive              13610 SW Harness Lane
Narragansett, RI 02882            Beaverton, OR 97008
401-284-1827                      503-430-1065
http://www.teraspeed.com%a0         503-246-8048 Direct
bob@teraspeed.com

Teraspeed is a registered service mark of Teraspeed Consulting Group LLC


-- 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/%a0       E-mail since 1993



      
-- 
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 Jul 7 03:58:36 2009

This archive was generated by hypermail 2.1.8 : Tue Jul 07 2009 - 03:59:39 PDT