Subject: using s2ibis2

From: "Betty Luk" <[email-masked]>
Date: Mon, 18 Sep 2000 15:43:27 -0400

Hello,

I have 2 questions regarding s2ibis2:

1) In the email sent by Dan Aleksandrowicz on Aug 13, 2000, he said that there is a version of s2ibis sofware that increases the resolution to 4 decimal places.  I recently downloaded s2ibis2 version 1.1 from the IBIS homepage, and the accuracy that I get is 2 decimal places.  Where can I get this fix for the 4 decimal place resolution?

2) I encountered a DC convergence problem when I was using s2ibis2 to generate an IBIS model for a 3-state Output pad (using HSPICE).  So, I manually changed the spice file generated by s2ibis2 for the pulldown curve to sweep from 6.6V to -3.3V in intervals of -0.1V (instead of its default from -3.3V to 6.6V in intervals of 0.1V).  In the resultant .ibs file, I don't think I'm getting the correct pulldown curve with the subtraction of the gnd clamp curve.  Is this because for s2ibis2 to generate the data correctly, the voltage values in the output file have to be increasing?  Any ideas on other workarounds?

Many thanks,

Betty Luk

IC Technology
Genesis Microchip Inc.
165 Commerce Valley Dr. W.
Thornhill, Ont. L3T 7V8
(905) 889-5400 x2256

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From: Syed Huq <[email-masked]>
Date: Tue, 19 Sep 2000 22:30:57 -0700 (PDT)

Betty, 

Not sure if you got any responses to your questions. My 2cents below:

> 1) In the email sent by Dan Aleksandrowicz on Aug 13, 2000, he said that there 
is a version of s2ibis sofware that increases the resolution to 4 decimal 
places.  I recently downloaded s2ibis2 version 1.1 from the IBIS homepage, and 
the accuracy that I get is 2 decimal places.  Where can I get this fix for the 4 
decimal place resolution?

You can find this 'fix' version at:
http://www.eda.org/pub/ibis/s2ibis/s2ibis2_v1.1/

Download the file called: s2ibis2_fix.tar.Z
Read the '00readme.txt' file for details after uncompressing and untar'ing.

> 
> 2) I encountered a DC convergence problem when I was using s2ibis2 to generate 
an IBIS model for a 3-state Output pad (using HSPICE).  So, I manually changed 
the spice file generated by s2ibis2 for the pulldown curve to sweep from 6.6V to 
-3.3V in intervals of -0.1V (instead of its default from -3.3V to 6.6V in 
intervals of 0.1V).  In the resultant .ibs file, I don't think I'm getting the 
correct pulldown curve with the subtraction of the gnd clamp curve.  Is this 
because for s2ibis2 to generate the data correctly, the voltage values in the 
output file have to be increasing?  Any ideas on other workarounds?
> Many thanks,

The pulldown curve from s2ibis2 does not subtract the gnd clamp. This is very 
visible if you plot the data points. I am unable to comment further since I do 
not know how your generated .ibs file looks like. Sometimes, I would reduce the 
sweep range to get away from convergence issues. Then I could extrapolate the 
end data points to the IBIS specified ranges(this is a valid approach).

Regards, 
Syed
Cisco Systems, Inc

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From: "Betty Luk" <[email-masked]>
Date: Wed, 20 Sep 2000 17:02:33 -0400

Hello Syed,

Thank you for your responses.

>>> Syed Huq <[email-masked]> 09/20/00 01:30AM >>>
>Betty, 

I have attached my .ibs file.  As a "trial", I have not included any package parasitics or c_comp.  I changed the sweep range from -3.3V - 6.6V to -2.7 - 6.6V to clear the convergence issue in the files pdtout.spi and ddtout.spi ("out" being the name of my output pin).  The file pdtout.spi specifies the typical pulldown curve spice file, and the file ddtout.spi specifies the pulldown curve with output disabled spice file.  (The [Ground clamp] curve is generated by another file, gctout.spi.)

It seems to me when I look at the resultant data in pdtout.out, ddtout.out and in the .ibs file under keyword [Pulldown], the subtraction was done by s2ibis2.  I have included excerpts from those files at the end of this message.  If s2ibis2 does not do the "subtraction", then wouldn't the simulator be "double-counting" the clamp curves when it's using the IBIS model? (Since it is stated in the IBIS specification that it is assumed the simulator will sum the clamp curves with the appropriate pullup or pulldown curves when the buffer is driving high or low.)

What method do you use to extrapolate the end data points?

Many thanks,
Betty Luk

****** file excerpt: pdtout.out
        volt    current                       vouts2i    -2.7000e+00    1.664e-01    -2.6000e+00    1.598e-01    -2.5000e+00    1.531e-01    -2.4000e+00    1.464e-01    -2.3000e+00    1.396e-01    -2.2000e+00    1.327e-01    -2.1000e+00    1.258e-01    -2.0000e+00    1.188e-01    -1.9000e+00    1.118e-01    -1.8000e+00    1.047e-01    -1.7000e+00    9.760e-02    -1.6000e+00    9.048e-02    -1.5000e+00    8.334e-02    -1.4000e+00    7.622e-02    -1.3000e+00    6.914e-02    -1.2000e+00    6.210e-02    -1.1000e+00    5.516e-02    -1.0000e+00    4.834e-02    -9.0000e-01    4.169e-02    -8.0000e-01    3.529e-02    -7.0000e-01    2.921e-02    -6.0000e-01    2.359e-02    -5.0000e-01    1.861e-02    -4.0000e-01    1.451e-02    -3.0000e-01    1.083e-02    -2.0000e-01    7.221e-03    -1.0000e-01    3.611e-03       0.          1.091e-10     1.0000e-01   -3.535e-03     2.0000e-01   -6.921e-03     3.0000e-01   -1.016e-02     4.0000e-01   -1.324e-02     5.0000e-01   -1.617e-02     6.0000e-01   -1.895e-02     7.0000e-01   -2.158e-02     8.0000e-01   -2.405e-02     9.0000e-01   -2.636e-02     1.0000e+00   -2.851e-02     1.1000e+00   -3.050e-02     1.2000e+00   -3.233e-02     1.3000e+00   -3.400e-02     1.4000e+00   -3.550e-02     1.5000e+00   -3.683e-02     1.6000e+00   -3.797e-02     1.7000e+00   -3.890e-02     1.8000e+00   -3.961e-02     1.9000e+00   -4.011e-02     2.0000e+00   -4.046e-02     2.1000e+00   -4.071e-02     2.2000e+00   -4.090e-02     2.3000e+00   -4.104e-02     2.4000e+00   -4.115e-02     2.5000e+00   -4.125e-02     2.6000e+00   -4.132e-02     2.7000e+00   -4.139e-02     2.8000e+00   -4.145e-02     2.9000e+00   -4.150e-02     3.0000e+00   -4.154e-02     3.1000e+00   -4.158e-02     3.2000e+00   -4.162e-02     3.3000e+00   -4.166e-02   

****** file excerpt: ddtout.out
        volt    current                       vouts2i    -2.7000e+00    1.215e-01    -2.6000e+00    1.154e-01    -2.5000e+00    1.093e-01    -2.4000e+00    1.031e-01    -2.3000e+00    9.695e-02    -2.2000e+00    9.075e-02    -2.1000e+00    8.454e-02    -2.0000e+00    7.832e-02    -1.9000e+00    7.211e-02    -1.8000e+00    6.592e-02    -1.7000e+00    5.976e-02    -1.6000e+00    5.365e-02    -1.5000e+00    4.761e-02    -1.4000e+00    4.167e-02    -1.3000e+00    3.585e-02    -1.2000e+00    3.019e-02    -1.1000e+00    2.474e-02    -1.0000e+00    1.953e-02    -9.0000e-01    1.467e-02    -8.0000e-01    1.021e-02    -7.0000e-01    6.294e-03    -6.0000e-01    3.133e-03    -5.0000e-01    9.967e-04    -4.0000e-01    1.728e-04    -3.0000e-01    1.994e-05    -2.0000e-01    1.351e-06    -1.0000e-01    4.619e-08       0.          1.098e-10     1.0000e-01   -1.066e-09     2.0000e-01   -1.158e-09     3.0000e-01   -1.210e-09     4.0000e-01   -1.254e-09     5.0000e-01   -1.293e-09     6.0000e-01   -1.331e-09     7.0000e-01   -1.367e-09     8.0000e-01   -1.401e-09     9.0000e-01   -1.436e-09     1.0000e+00   -1.470e-09     1.1000e+00   -1.504e-09     1.2000e+00   -1.537e-09     1.3000e+00   -1.570e-09     1.4000e+00   -1.603e-09     1.5000e+00   -1.636e-09     1.6000e+00   -1.670e-09     1.7000e+00   -1.702e-09     1.8000e+00   -1.735e-09     1.9000e+00   -1.769e-09     2.0000e+00   -1.802e-09     2.1000e+00   -1.836e-09     2.2000e+00   -1.871e-09     2.3000e+00   -1.905e-09     2.4000e+00   -1.941e-09     2.5000e+00   -1.977e-09     2.6000e+00   -2.015e-09     2.7000e+00   -2.054e-09     2.8000e+00   -2.080e-09     2.9000e+00   -2.086e-09     3.0000e+00   -2.093e-09     3.1000e+00   -2.096e-09     3.2000e+00   -2.102e-09     3.3000e+00   -2.107e-09