Re: FAQ #6 and #7 revised....

Text item:

Syed,

I would combine the very last two paragraphs into one (in #7).

Regarding #6, I was expecting to read something about the [Pin Mapping] keyword.
To be able to do good GND bounce simulations one must know how many buffers are
getting their supply current through the same power and GND pins. Your answer
does not address this side of the issue, only the L,R,C part. Could you add
this to it?

Arpad
===============================================================================
IBISfans,

As mentioned in the last IBIS Minutes (Aug11th'95), the last two
FAQ that need to be re-worded were #6 and #7.

I am attaching the revised answers based on some inputs I received.

Pls post your comment/changes/suggestions on the reflector and we
shall vote on this on the Aug25th meeting.

Regards,
Syed.
National Semiconductor.

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6.0 Can IBIS model SSO(Simultaneous Switching Output) ?

IBIS as a model, has all the parameters required to model an SSO event. These
are mainly the package inductance parameters and other associated parasitics.
IBIS specifies R, L and C in matrix format and the use of a matrix for the
inductance accounts for the "loop"inductance i.e. the mutuals between the
pins. Specifying the mutual inductance is necessary to account for SSO event
simulation. Modeling an SSO event is more of a simulator issue than IBIS.

7.0 Why do we need to sweep -Vcc to 2Vcc ?

Simulation accuracy is greatly enhanced by the "beyond-the-rail" data.
Overshoot and undershoot generally fall within this range, and the range
encompasses the forward-biased regions of protection diodes often used on
buffers. Also, reflections caused by improper terminations can produce
voltages at the driver/receiver terminals from -Vcc to 2Vcc. The drivers
and receivers, therefore, need to be modeled over this entire range.

Since measurement of diodes over the entire range is often not possible,
measurement over a reasonable range and extrapolation of data to the
end-point values is permitted to produce IBIS models.

Most non-SPICE based simulators will do their own extrapolation to get to
the end point. Most Spice simulators truncate data to the table
end-points.

The -Vcc to 2Vcc range ensures consistent performance for both types of
simulators.
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Subject: FAQ #6 and #7 revised....
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From: huq@rockie.nsc.com (Syed Huq)
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