Hi Andrew,
Hopefully you know this but let me start from basic:
-VDD to 2VDD range is chosen for sweep to take care of worst case
reflections seen for open and short transmission line.
CMOS or IO behaviour is predictable and extrapolation will work for those
voltages, if at all any such worst case condition happens.
If you are still interested in capturing that behaviour I suggest change
typical voltage to corner you are interested in and do the sweep
accordingly(take reference from below).
Simulate it and the model generated earlier and overlap output waveforms,
and see if there is any difference.
Just for record and understanding sweep range in detail:
Let's say we have Vddio
Typ:1.8V
Min 1.65V
Max: 1.95V
Change IO supply for respective corners in different decks.
Sweep is done at pad pin which you are modeling and step size is same
across corners.
We keep a fixed Vgs and vary Vds by varying drain voltage at pad pin for
pull-up and pulldown data capture.
So table Voltage in IBIS model always refers to Vds. So for pulldown ground
referenced data, Vds same as pad voltage.
Now when you generate data for gnd referenced tables like Pull down sweep
range stays same across corners.
Sweep range for
Typ: -1.8V to 3.6V
Min: -1.8V to 3.6V
Max: -1.8V to 3.6V
For power referenced pullup think of Vds and not the sweep voltage at pad
pin.
Sweep range changes to take care of corners:
Typ: -1.8V to 3.6V
Min: -1.95 to 3.45V
Max: -1.65 to 3.75V
This way you ensure number of points are same across corners for same step
size.
Calculations
Min case:
Pad voltage(Vd)sweep point -1.95,
Vddio(Vs) 1.65
So Vds is 3.6,
Typ case:
Pad voltage(Vd) sweep point -1.8,
vddio(Vs) 1.8
So Vds 3.6
Max case:
Pad voltage(Vd) sweep point -1.65
Vddio(Vs) 1.95
So Vds 3.6
hence we choose the sweep range this way that same Vds point is captured
for all corners.
Number of points are same for all corners if we keep step size same and
choose sweep range like above.
Hope it helps. Feel free to ask if any more doubt.
Thanks
Pankaj Gupta
On Wed, 3 Apr, 2024, 11:27 pm Andrew Phelps, <Andrew.Phelps@xxxxxxxxx>
wrote:
Hi Pankaj,
I’m not sure I understand your comments; if you have different Vdds for
typical, minimum, and maximum, you can have either the same step size or
number of steps, but not both.
If you only use the typical range, you will not be able to fully cover the
maximum range, or where the supply is some percent positive from nominal.
From this comment:
“While simulating, Simulators will read (Voltage Range) keyword values and
automatically adjust VI data covering entire range for each corner.”,
It sounds like you are saying the simulator will extrapolate the data. I
am trying to remove that potential source of error.
Thanks!
Andrew
*From: *pankaj gupta <pankaj26492@xxxxxxxxx>
*Date: *Wednesday, April 3, 2024 at 1:15 PM
*To: *Lance.Wang@xxxxxxxxxxxx <Lance.Wang@xxxxxxxxxxxx>, Andrew Phelps <
Andrew.Phelps@xxxxxxxxx>
*Cc: *ibis@xxxxxxxxxxxxx <ibis@xxxxxxxxxxxxx>
*Subject: *Re: [ibis] FW: IBIS Voltage Sweep question
**This email has been sent from an* EXTERNAL* source**
Hi Andrew,
For data generation do sweep for respective Vdd value for each corner:
-Vdd to 2Vdd
Step size is same and hence total number of points remain same for each
corner.
While putting data, simply use typical voltage value in V column and each
corner current data irrespective of voltage value but point by point. If
you have an eda tool or s2ibis3, that will be done automatically.
While simulating, Simulators will read (Voltage Range) keyword values and
automatically adjust VI data covering entire range for each corner.
Trick is to get sweep range for power reference data like power clamp and
pull-up.
Thanks
Pankaj Gupta
On Wed, 3 Apr, 2024, 8:40 pm Wang Lance, <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
Hi Andrew,
Thanks for the question about IBIS.
I am forwarding your question to ibis reflector. Many experts are there
and they may answer your questions directly.
Meanwhile, if you hadn’t yet. I would suggest you subscribe IBIS reflector
at https://freelists.org/list/ibis
<https://urldefense.com/v3/__https:/freelists.org/list/ibis__;!!LUcoR2A!Px0lNNUezf6nz4hrSGnxvJJAXw87afTzcpdTVWRyFK6z8kWbYgjs9rhJARG-L_gJp3Gic86AjcKB2LO1wfZLVYQk$>.
It will enable you for better connections in IBIS Committee.
Please feel free to contact me for any questions.
People@ibis reflector, Please copy Andrew directly when you answer his
question.
Thanks for supporting IBIS.
Best regards,
Lance
*Lance Wang*
Chair, IBIS Open Forum
*Email*: Lance.Wang@xxxxxxxx
*www.ibis.org*
<https://urldefense.com/v3/__http:/www.ibis.org/__;!!LUcoR2A!Px0lNNUezf6nz4hrSGnxvJJAXw87afTzcpdTVWRyFK6z8kWbYgjs9rhJARG-L_gJp3Gic86AjcKB2LO1wdX9Itsu$>
*From:* Andrew Phelps <Andrew.Phelps@xxxxxxxxx>
*Sent:* Wednesday, April 3, 2024 10:51 AM
*To:* info@xxxxxxxx
*Subject:* IBIS Voltage Sweep question
Hello,
I have a question about performing voltage sweeps for pullup, pulldown,
etc, when looking at minimum and maximum conditions. Below is an excerpt
from the IBIS Modeling Cookbook for IBIS version 4.0, page 16:
[image: A text on a page Description automatically generated]
While this 9.9V sweep range covers the minimum voltage, I don’t think it
would cover the maximum voltage condition, which would range from -3.6V to
7.2V. Does that mean that this range needs to be 10.8V for all sweeps,
including the typical and minimum condition? Otherwise I don’t think you
have all the data you need, since the step size for the sweeps shouldn’t
change from voltage to voltage, or at least that is my understanding of the
IBIS standard.
Thanks!
Andrew
