Subject: RE: [IBIS-Users] Vinh for Differential Part
From: Tom Dagostino (tom@teraspeed.com)
Date: Fri Dec 06 2002 - 13:40:02 PST
The problem with setting Vdiff to 0 is slow slew rates or poor transitions
will not give accurate timing. All of the datasheets that I checked had a
limitation on the maximum transition time (between 1 and 5 nsec) for the
Vdiff = 0 timing.
Tom Dagostino
Device Modeling Division
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 430-1065
tom@teraspeed.com
http://www.teraspeed.com
-----Original Message-----
From: vinu@cisco.com [mailto:vinu@cisco.com]
Sent: Friday, December 06, 2002 12:40 PM
To: tom@teraspeed.com
Cc: 'Timothy Coyle'; ibis-users@eda.org
Subject: Re: [IBIS-Users] Vinh for Differential Part
The device might switch when the differential inputs are 100mV apart.
However,
if the datasheet timing reference point is the zero crossing, Vdiff should
be
set to 0 in the IBIS model and the simulator should use this Vdiff value to
report timing. Setting a different Vdiff value like 100mV in the IBIS model
will result in a timing inaccuracy due to double counting. Likewise for
Vinh/Vinl.
Thanks,
Vinu
Tom Dagostino wrote:
> The switching point for a differential input happens when the difference
in
> the input voltage reaches the Vdiff value. In this case the common mode
> voltage is 1.2 Volts and the inputs need to be at least 100 mV different
to
> cause the input to recognize state. Thus 1.15 and 1.25 volts would be the
> appropriate Vinl/Vinh values.
>
> Tom Dagostino
> Device Modeling Division
> Teraspeed Consulting Group LLC
> 2926 SE Yamhill St.
> Portland, OR 97214
> (503) 430-1065
> tom@teraspeed.com
> http://www.teraspeed.com
>
> -----Original Message-----
> From: owner-ibis-users@server.eda.org
> [mailto:owner-ibis-users@server.eda.org]On Behalf Of Vinu Arumugham
> Sent: Friday, December 06, 2002 9:30 AM
> To: Timothy Coyle
> Cc: ibis-users@server.eda.org
> Subject: Re: [IBIS-Users] Vinh for Differential Part
>
> Since these threshold voltages are used for timing measurements and since
> datasheets specify timing at the zero crossing or Vddq/2 level, would it
not
> be better to set Vdiff=0, Vinl=Vinh=1.2V?
>
> Thanks,
> Vinu
>
> Timothy Coyle wrote:
>
> > Hello,
> > I have a differential device in an IBIS file. I define a Vdiff of 100mV
> > for my differential signal thresholds. However, I also have to define a
> > Vinh and Vinl
> > for the single-ended positive and negative differential Input model
types
> > in IBIS. The IBIS spec (3.2) states that:
> >
> > If a pin is a differential input pin, the differential input
> > | threshold (vdiff) overrides and supersedes the need for Vinh
> > | and Vinl.
> >
> > However, if I do not define a Vinh and Vinl for my differential inputs,
> > then the IBIS parser gives me a warning. It also seems that some
> > simulators use this
> > Vinh and Vinl for the single-ended differential signals. If this is an
> LVDS
> > input, switching from 1 to 1.4 V, then I could put thresholds of 1.1 and
> > 1.3?
> >
> > I'm curious as to what other people do and why the parser gives me this
> > warning?
> >
> > Regards,
> > Tim
> >
> > |------------------------------------------------------------------
> > |For help or to subscribe/unsubscribe, email majordomo@eda.org
> > |with just 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 email a written request to ibis-request@eda.org.
> > |
> > |IBIS reflector archives exist under:
> > |
> > | http://www.eda.org/pub/ibis/email_archive/ Recent
> > | http://www.eda.org/pub/ibis/users_archive/ Recent
> > | http://www.eda.org/pub/ibis/email/ E-mail since 1993
>
> |------------------------------------------------------------------
> |For help or to subscribe/unsubscribe, email majordomo@eda.org
> |with just 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 email a written request to ibis-request@eda.org.
> |
> |IBIS reflector archives exist under:
> |
> | http://www.eda.org/pub/ibis/email_archive/ Recent
> | http://www.eda.org/pub/ibis/users_archive/ Recent
> | http://www.eda.org/pub/ibis/email/ E-mail since 1993
|------------------------------------------------------------------
|For help or to subscribe/unsubscribe, email majordomo@eda.org
|with just 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 email a written request to ibis-request@eda.org.
|
|IBIS reflector archives exist under:
|
| http://www.eda.org/pub/ibis/email_archive/ Recent
| http://www.eda.org/pub/ibis/users_archive/ Recent
| http://www.eda.org/pub/ibis/email/ E-mail since 1993
This archive was generated by hypermail 2b28 : Fri Dec 06 2002 - 13:54:22 PST