Subject: [IBIS-Users] Query on the IBIS file verification
From: radhika.guttal@wipro.com
Date: Sun Jan 04 2004 - 21:44:45 PST
Hi Experts,
I have found some interesting behavior of IBIS models during
verification using HSPICE simulator. I would like to get your comments
on the following :
1. I have generated an IBIS model for a 3-state Output buffer. When I
disable the output buffer IBIS model and give a sweep voltage from
-ref_voltage to 2*(ref_voltage) on the output pin (just as is done to
generate the IV tables for IBIS model), I get very small currents in
order of uA even on beyond rail voltage values. Now at above the rail
voltages, I would expect some good amount of current as clamp diodes
would be turned on. The clamp tables in the IBIS model do have currents
in Amperes at above rail voltages. But when I enable the buffer and then
apply a sweeping voltage on the output pin I get expected current
values. Any comments on why I am not able to get clamp table value
currents when the buffer is disabled ?
2. In one of the I/O buffer IBIS model transient analysis, the ouput
waveform does not match the model's V-T table. I am using the same setup
(same Rload with same termination and same input signal used to generate
the IBIS model) for the analysis. I am not able to figure out the
mismatch. When I run ibischk3 on the IBIS model I am getting the
following warnings which I am not able to eleminate :
a. The [Rising Waveform] with [R_fixture]=50 Ohms and
[V_fixture_max]=1.6V has MAX column DC endpoints of 0.76V and 1.59V,but
an equivalent load applied to the model's I-V tables yields different
voltages(0.76V and 1.57V), a difference of 0.21% and 2.22%,respectively.
b. The [Falling Waveform] with [R_fixture]=50 Ohms and
[V_fixture_max]=1.6V has MAX column DC endpoints of 0.76V and 1.59V,but
an equivalent load applied to the model's I-V tables yields different
voltages(0.76V and 1.57V), a difference of 0.21% and 2.22%,respectively.
If anybody has faced the same problem or has some solution for the above
issues please guide me in this regards,
Radhika V Guttal
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