Subject: RE: [IBIS-Users] Vinh for Differential Part
From: Tom Dagostino (tom@teraspeed.com)
Date: Fri Dec 06 2002 - 09:46:09 PST
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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