Subject: Bi-polar power supplies in IBIS

From: Stephen Nolan <[email-masked]>
Date: Mon, 03 Apr 2000 19:26:09 -0500

IBIS-users,

Is it possible, using IBIS, to model devices that use bi-polar power supplies?
For example data-transmission devices, like RS-232, that use a +15 V and -15 V
supply? 

If so, how is the pull-down modeled? Is the Pull-down VI table -Vcc referenced
instead of ground referenced?

Thanks.
-- 
Regards,
Stephen M. Nolan

---

From: Mike LaBonte <[email-masked]>
Date: Mon, 03 Apr 2000 23:03:53 -0400

I think the basic requirement is that the output has 2 voltage or current levels.
So if the encoding is NRZ-L or Manchester, then an IBIS model should work. But if
something like Bipolar AMI (3 voltage levels) is used, then IBIS falls apart because
IBIS is currently predicated on binary signaling.

We call them power and ground for familiarity, but they can be thought of as high
and low supply voltages with a current loop path. If the output doesn't go rail to
rail, some DC offset can be built into the VI curves. So a +15/-15 power supply might
result in output signals that swing between 0 and +12V, for example.

Mike