Subject: Re: [IBIS-Users] Vinh for Differential Part
From: Vinu Arumugham (vinu@cisco.com)
Date: Fri Dec 06 2002 - 12:39:34 PST
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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