Re: V/I table in Bench measurements

Steven, Syed,

Now that I am back from my vacation, here is my opinion on these questions:

The reason we require these "extreme" ranges in the models is to make sure that
all simulators handle the curves as they should in such extreme situations. If
you can not measure that far, make an intelligent extrapolation to extend the
data to the required range.

Regarding the TTL device in a 5V environment, in my opinion, it should still use
-5V to +10V, because there might be another device in the system that is CMOS,
and very well overshoot beyond 7V.

I feel that the ordering of the voltage should go from -V to +V and not +V to
-V, because SPICE can not handle decreasing voltage tables in their PWL sources.
For those who are using IBIS models on SPICE platforms this is important.

Arpad Muranyi
Intel Corporation

Hello Bob, Syed:

     You know, Syed's question brings up an interesting point. Suppose the
     VCC of a device is at +5V but the output is TTL and the maximum swing
     is, say 3.5V. Should the output be characterises from -3.5 to 7.0v
     (the maximum voltage range that the output would ever realistically
see)
     or does one still have to do the -5 to +10v range?

                  Best Regards,
                  Stephen Peters
                  Intel Corp.

Hi fellow gurus:

        Got two questions about the V/I table.

1) Does the Voltage table need to ramp down from a -ve number to
a +ve or can it
   be from +ve to -ve number as well ?
   Ex: For [Pulldown] the Voltage table goes from -5.0V to +10.0V

2) For most of the V/I table, IBIS shows that the voltage range should
go from
   +10V to -5V. Problem is, there are devices whose I/O structure
cannot handle
   swings that large. In that case, since we should not test a device beyond
   it's Absolute Recommended Operating(ABS Max) range, is it O.K
 NOT to swing
   the I/O all the way to +10 to -5V ???

Regards,
Syed huq
National Semiconductor
Received on Mon Jul 25 10:35:39 1994