Subject: How to correct the monotonicity problem of ibis model when importing model to ICX?

From: "Olli Timonen" <[email-masked]>
Date: Wed, 10 May 2000 14:02:56 +0300

Hello!

I tried to import an ibis model to ICX. It reports following errors of non
monononicity:

Error: The sum of the typical clamp curves is not monotonic at voltage 1.6
Error: The sum of the minimum clamp curves is not monotonic at voltage 2.1
Error: The sum of the maximum clamp curves is not monotonic at voltage 2.6

!! the model in question is in the end of this message !!

What is the best way to modify this model to make it compatible with ICX? Does
simulation distort significantly if I just change all the I-values to zeros
after voltage has turned positive?

Second question:

What is the good (best) way to define Vmeas value if it isn't included in the
model and can't be found from the datasheets, etc. (maybe Vdd*0.5?)?

********************************************************

[Model]            ptic
Model_type        Input
Polarity   Non-Inverting
Enable      Active-Low
Vinl =       0.8000V
Vinh =        2.000V
C_comp         5.0pF           5.0pF           5.0pF

[Temperature Range]    25.0000      85.000      -40.0000
[Voltage Range]         3.3000V     2.9700V      3.6300V
[GND_clamp]
| voltage     I(typ)           I(min)        I(max)

-3.30          -0.761         -0.682         -0.999
-3.20          -0.712         -0.641         -0.928
-3.10          -0.664         -0.601         -0.859
-3.00          -0.618         -0.563         -0.794
-2.90          -0.574         -0.526         -0.731
-2.80          -0.531          -0.49          -0.67
-2.70           -0.49         -0.455         -0.612
-2.60          -0.451         -0.421         -0.557
-2.50          -0.413         -0.388         -0.504
-2.40          -0.376         -0.357         -0.454
-2.30          -0.342         -0.327         -0.407
-2.20          -0.308         -0.298         -0.362
-2.10          -0.277          -0.27         -0.319
-2.00          -0.247         -0.244          -0.28
-1.90          -0.219         -0.219         -0.243
-1.80          -0.188         -0.191         -0.208
-1.70          -0.166         -0.171         -0.172
-1.60          -0.145         -0.151         -0.147
-1.50          -0.124         -0.131         -0.123
-1.40          -0.104         -0.112         -0.101
-1.30         -0.0847        -0.0933        -0.0784
-1.20         -0.0659        -0.0751        -0.0576
-1.10         -0.0483        -0.0579        -0.0387
-1.00          -0.032        -0.0416        -0.0221
-0.90          -0.018         -0.027        -0.0099
-0.80         -0.0079        -0.0147       -0.00469
-0.70        -0.00311       -0.00627       -0.00265
-0.60        -0.00144       -0.00228       -0.00121
-0.50       -0.000504      -0.000854      -0.000315
-0.40       -7.55e-05      -0.000237      -2.37e-05
-0.30       -2.96e-06      -2.93e-05      -3.18e-07
-0.20          -8e-08      -1.65e-06      -1.28e-08
-0.10          -6e-09      -7.53e-08      -1.75e-09
0.00          -4e-09      -7.75e-09       3.25e-09
0.10          -1e-09       -2.5e-09       9.25e-09
0.20          -2e-09        2.5e-10       1.43e-08
0.30        -2.5e-09       -2.5e-10       1.57e-08
0.40          -4e-09       -7.5e-10       1.98e-08
0.50        -2.5e-09         -1e-09        2.2e-08
0.60          -2e-09          5e-10        2.7e-08
0.70          -3e-09          1e-09       3.12e-08
0.80          -1e-09       -1.5e-09        3.5e-08
0.90          -3e-09         -5e-10       3.98e-08
1.00          -2e-09       -7.5e-10       4.22e-08
1.10          -2e-09       -3.5e-09        4.5e-08
1.20               0      -1.96e-07       4.93e-08
1.30          -5e-09      -5.23e-06        5.1e-08
1.40       -2.99e-07      -1.05e-05       5.15e-08
1.50       -1.64e-05      -1.35e-05      -3.01e-06
1.60       -2.03e-05       -1.4e-05      -1.49e-05
1.70       -2.12e-05      -1.39e-05      -2.99e-05
1.80       -2.15e-05      -1.32e-05      -3.21e-05
1.90        -2.1e-05      -2.32e-05      -3.26e-05
2.00       -2.02e-05      -3.13e-05      -3.24e-05
2.10          -2e-05      -0.000108      -3.18e-05
2.20          -2e-05      -0.000168      -3.05e-05
2.30          -2e-05      -0.000152      -5.53e-05
2.40          -2e-05      -5.97e-05      -7.74e-05
2.50          -2e-05      -1.16e-05      -0.000134
2.60          -2e-05      -1.37e-06      -0.000245
2.70          -2e-05      -1.32e-07      -0.000562
2.80       -1.84e-06       -1.1e-08       -0.00048
2.90       -1.17e-07       1.25e-09      -0.000223
3.00          -1e-08       1.25e-09      -6.41e-05
3.10        -5.5e-09        2.5e-09       -9.3e-06
3.20          -1e-09          5e-09      -5.43e-07
3.30          -2e-09       1.05e-08       8.95e-08

[POWER_clamp]
| voltage      I(typ)         I(min)         I(max)

-3.30           0.388          0.281          0.525
-3.20           0.365          0.264          0.494
-3.10           0.343          0.248          0.464
-3.00           0.321          0.232          0.434
-2.90             0.3          0.216          0.406
-2.80            0.28            0.2          0.378
-2.70            0.26          0.186          0.352
-2.60           0.241          0.169          0.326
-2.50           0.222          0.156          0.301
-2.40           0.204          0.144          0.277
-2.30           0.187          0.131          0.254
-2.20           0.168          0.119          0.233
-2.10           0.154          0.107          0.212
-2.00            0.14         0.0948          0.192
-1.90           0.127         0.0828          0.169
-1.80           0.113          0.071          0.153
-1.70           0.101         0.0595          0.138
-1.60          0.0876         0.0484          0.122
-1.50          0.0748         0.0377          0.107
-1.40          0.0625         0.0279         0.0935
-1.30          0.0507          0.019         0.0796
-1.20          0.0396         0.0116         0.0665
-1.10          0.0295        0.00559         0.0543
-1.00          0.0205        0.00106         0.0428
-0.90          0.0127       0.000111         0.0321
-0.80         0.00535       8.34e-06         0.0219
-0.70        0.000761       7.24e-07          0.013
-0.60        4.39e-05       1.12e-07        0.00507
-0.50        1.37e-06       2.93e-08       0.000549
-0.40         4.5e-08       1.05e-08       2.08e-05
-0.30               0          5e-09       4.82e-07
-0.20          -1e-09        2.5e-09       1.48e-07
-0.10        -2.5e-09       1.25e-09       1.34e-07
 0.00          -2e-09       1.25e-09       1.29e-07

---

From: Bob Ross <[email-masked]>
Date: Wed, 10 May 2000 10:09:56 -0700

Olli:

I will respond briefly to your questions.

For non-monotonic data problem, it appears that your
suggestion of just zeroing out the noisy data should
eliminate the Error reports.  This approach should not
effect accuracy.  There may be other options that could
be discussed directly with the vendor.

There probably is not a completely general answer for
selecting a Vmeas when none can be found.  It is needed
if any timing delay data is specified.  My first
approach would be to select a value that is somewhere
midway between the input threshold voltages for the
input techology that the I/O buffer is designed to
drive.

Best Regards,
Bob Ross
Mentor Graphics

---

From: Al Davis <[email-masked]>
Date: Wed, 10 May 2000 09:28:16 -0700

> after voltage has turned positive?

The non-monotonic stuff looks like measurement noise to me.
You won't lose anything by just making it zero.  The
simulator probably does this anyway.

Non-monotonic means there is a negative resistance region. 
This means the circuit is probably unstable, which means it
is will oscillate in some conditions.  The real circuit
probably doesn't do this.  You are probably improving the
accuracy of the model if you flatten out the questionable
areas.  Just remove or comment out the offending lines.

The real device inside that is being modeled by a clamp
curve is usually a diode.  Diodes don't do that.  A proper
clamp curve should be zero, or at least nearly zero, with
current in the correct direction, in its reverse biased
region.