Subject: [IBIS-Users] LVDS driver VT curves selection
From: Henrik G. Madsen (hgm@vitesse.com)
Date: Fri Nov 29 2002 - 07:35:20 PST
Hey all
I have read most of the latest presentations on making IBIS models for LVDS drivers with interest, but....
How many VT curves to include in the initial model?
For very short tracks (I.e. the 100 ohm diff termination very close to the driver, no transmission line), two waveforms should be enough
[Rising waveform] 50 Vcm(typ) Vcm(min) Vcm(max) NA NA NA NA NA
[Falling waveform] 50 Vcm(typ) Vcm(min) Vcm(max) NA NA NA NA NA
where Vcm(???) is the out common mode voltage
To include the cases where the driver is connected to a transmission line with a diff impedance of 100 ohm, the following waveforms should be made too
[Rising waveform] 50 Vol(typ) Vol(min) Vol(max) NA NA NA NA NA
[Falling waveform] 50 Voh(typ) Voh(min) Voh(max) NA NA NA NA NA
(The driver sees a 100 ohm transmission line, but since both pads change opposite, the real voltage swing is the double. To include that in the above I have halfed the impedance)
Is more waveforms needed?
_____________________________________
Henrik G Madsen
Sr. HW Engineer
Vitesse Semiconductor Corporation A/S
Ethernet Products Division
Hoerkaer 16, DK-2730 Herlev, DENMARK
Direct: +45 4485 5920
Phone: +45 4485 5900, Fax: +45 4485 5901
mail: hgm@vitesse.com
web: http://www.vitesse.com
_____________________________________
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