Subject: Re: AW: [IBIS-Users] I-V vs V-T curves
From: Ross, Bob (bob_ross@mentorg.com)
Date: Wed Apr 24 2002 - 18:10:30 PDT
Hello Tim:
Actually, ibischk3 should work correctly for any set of
waveform endpoints based on R_fixture and V_fixture values.
The manual calculation of voltage can be done by iteration.
You assume a voltage, and then calculate the current needed
to supply R_fixture and V_fixture for either the high state
hen you add up the currents supplied by the [Pullup] table
(plus the [Gnd Clamp] and [Power Clamp] tables for the assumed
voltage.
If the currents are different, readjust the voltage in
the correct direction and repeat. Eventually you should
converge on the solution.
Then you repeat this process for the low state using the
[Pulldown] table and clamps.
Bob Ross
Mentor Graphics
Lenski Eckhard wrote:
>
> Hello Tim,
>
> I assume that you are modeling an LVDS-output.
>
> Normaly ( cmos ) you compare the crossing of the 50Ohmload curves with the
> pullup - pulldown curves
>
> - 50 Ohm to Gnd crossing with pullup curve
> - 50 Ohm to Vcc crossing with pulldown curve
>
> and the rising falling waveforms are measured with a 50 Ohm load to GND and
> to VCC.
>
> For LVDS you have to look for the crossing of your 50 Ohm to 1.2V load-curve
> with the pullup and pulldown curves
> ( so you havve to use the same loadcurve twice )
> and then there should be no ( or no significant ) mismatch.
>
> By the way, I think the ibis-checker is always using 50 ohm to gnd and 50 Ohm
> to vcc.
>
>
> If you have further questions, please let me know.
>
> regards
> Eckhard Lenski
>
>
> Eckhard Lenski
> Siemens AG
> ICN WN OP TDC TC3
> 81359 München
> Tel: 0049 89 722 27776
> Fax: 0049 89 722 44692
> Email: eckhard.lenski@icn.siemens.de
>
> -----Ursprüngliche Nachricht-----
> Von: Timothy Coyle [mailto:Timothy.Coyle@nsc.com]
> Gesendet: Freitag, 19. April 2002 20:24
> An: ibis-users@eda.org
> Betreff: [IBIS-Users] I-V vs V-T curves
>
> Hi,
> I am trying to determine where my mismatch end points are coming
> from in an IBIS file I am creating. How do I get the end points
> from the pullup and pulldown I-V data
> so I can compare them to the endpoints in my V-T curves? (load
> condition for V-T data is 50 ohms to 1.2V with endpoints 1.0V and
> 1.4V)
>
> Thanks,
> Tim
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