Subject: Re: [IBIS-Users] Vinh for Differential Part
From: Fred Balistreri (fred@apsimtech.com)
Date: Fri Dec 06 2002 - 13:46:53 PST
Why not use Vmeas or Vinh, Vinl which would be more accurate. I think
Tom is right on this one.
Best Regards,
Tom Dagostino wrote:
>
> 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
> > >
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-- Fred Balistreri fred@apsimtech.comhttp://www.apsimtech.com |------------------------------------------------------------------ |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
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