Re: IBIS BIRD67.1 - Increase V-T Table 100 Point Limit

On Fri, 03 Nov 2000, Matthew Flora wrote:
> Will this increase to the data point quantity limit be retroactive to IBIS
> 3.0, 3.1, 3.2, or does it only apply to 3.3 and later? I ask because I want
> to make sure that IBISCHK will make the distinction.

It seems to me that obviously it can only apply to future versions,
because we cannot change products that have already been shipped to
customers.

I do not oppose an increase in the table size to something
arbitrarily large, like 1000 points. Most tools use dynamic
allocation anyway, and for those that don't it is usually just
changing the subscript on an array. The only reason I see to not
make it completely unlimited is to not require a major rewrite for
simulators that use fixed allocation. I agree with the increase,
because most is not all, and the standard should not arbitrarily
prohibit the few cases where the increase in points is truly needed.

However, in most cases the existing 100, or even 30, is plenty of
points. Accuracy is limited elsewhere.

Many models have only one waveform of each type, which is measured
with a particular load. Even if the measurement is highly accurate
with that load, the waveform is only a guess with any other load.
Therefore, accuracy can be better by supplying additional waveforms
with diffrerent loads, or loads to different reference voltages.
This is true in the extreme with differential drivers, where the only
correct load is the differential one, with the other end connected to
the other side's driver.

Another issue is proper choice of the time points. Many have 100
points, but all of the action is in 3 points. First, there are too
few points in the action region. Second, and as important, data in
the nearly steady region is often contaminated by noise or limited by
numeric granularity.

Consider ......
0 0.22
1n 0.22
2n 0.22
3n 0.22
4n 0.23
5n 0.23
6n 0.23
7n 0.23
8n 0.24
9n 0.24

You might naively interpret this to mean the voltage is increasing
slowly. What the data says is that it remains constant until 4ns,
then jumps , remaining constant again until 8ns, jumping again. If
this is driving a capacitor, you get a current spike at 4ns and 8ns,
with no current elsewhere.

But, likely the intent is that the voltage is increasing slowly.
Accuracy is actually improved by removing points, in this case giving
only 0, 4n, and 8n.
 
Received on Fri Nov 3 17:20:06 2000