QUESTIONS AND ISSUES

Greetings IBIS folks:

Below are some points in IBIS Version 1.0 which I believe
need clarification before Version 2.0 is finalized. Also,
some issues are raised which call for some format changes,
so I hope these can be resolved quickly.

I. PACKAGE MODEL AND PIN MODEL

What is the model?

        DIE----R_pkg----L_pkg----C_pkg----PIN
or

        DIE----R_pkg----C_pkg----L_pkg----PIN

The first case is used in the Pentium and PCI models from
Intel and the second case exists in the TI Spice models.

I would support a more robust model that allows for both
cases by replacing R_pkg with C_pkd.

        DIE----C_pkd----L_pkg----C_pkg----PIN

Based on the range of typical values and lack of specification,
I believe that R_pkg has an insignificant effect in the
analysis and is inserted primarily to assist in convergence
when running Spice models. The substitution of "R_pkg" with
"C_pkg" would be useful for these reasons:

  (1) Provide compatiblity with either of the first two models
      above (zero or NA would be one of the C_pk* entries).
  (2) Provide the opportunity for a better package model by
      distributing the C-package value.

II. RAMP dV/dt_r AND dV/dt_f "MIN" AND "MAX"

A presumption exists that the PULLDOWN, PULLUP, GND_CLAMP and
POWER_CLAMP "min" and "max" entries are associated with the
"min" and "max" VOLTAGE RANGE values so that the unloaded
ramp amplitiude can be obtained from the voltage offset at
0.0 Amps.

(1) For consistency and extrapolation purposes, should the "min"
and "max" entries of the RAMP dV/dt_r and dV/dt_f also be
associated with VOLTAGE RANGE "min" and "max" values? Or (2),
should they always be the true min and max dV/dt values?
Or (3), should they always correspond to the fastest and slowest
time values? I have seen all three cases, but favor (1).

III. Vtable DEFINITION

For PULLUP and POWER_CLAMP, Vtable is defined as

        Vtable = Vcc - Voutput

This creates an unusual polarity reversal that appears totally
unnecessary. A negative entry corresponds to a positive
offset from Vcc, and visa-versa. What value does this
provide?

A better definition would be:

        Vtable = Voutput - Vcc

This will permit the Vtable offset entries to track with
Voutput values, providing a more readable and understandable
table. Offsets referenced to other supplies such as Vee
would follow a similar definition for consistency and
also would track with Voutput changes.

I would like to see this change made before too many models
are generated in compliance with the original definition.
Alternatively, Version "1.X" models could conform to the
original definition, Version "2.X" and above to the revised
definition where the simulator handles the polarity change
based on Version number.

IV. SPECIFIED VOLTAGE RANGES

In section 2) of "NOTES ON DATA DERIVATION METHOD" at the
end, no explaination is given why the voltage ranges for the
GND_CLAMP and POWER_CLAMP are different.

My preference is to relax the voltage range requirements
for the 2.0 release and rely on vendors providing reasonable
ranges. Simulators easily can do (linear) extrapolation to
go beyond the supplied ranges.

The required ranges go well beyond what is reasonable for
measurement correlation (an explicit goal) and extraction.
For example, it is required that a clamp diode (or sensitive
ESD circuit) be forward biased to, say, 5 volts in order to
extract a 4 Amp current value (20 Watts !!). The "measured"
value would normally have to be obtained from extrapolating
values at lower voltages since a direct measurement done
without using pulsing techniques would damage the device.
In general, I do not believe the standard should require
data that clearly falls outside a part's maximum ratings.

Thanks, Bob Ross (Interconnectix, Inc.)
Received on Fri Aug 27 14:04:34 1993