RE: [IBIS-Users] IV clamp range

Lynne,

Thanks for your comments.
We are seeing gnd and powerclamp showing the crossovers.
Please see attached.

We do not see crossover in the normal range 0 to VCC since the ESD diodes are not on.
We use same voltage range in the ibis model. But my concern is since the spice attached is showing the crossover.
Is there anything that I need to do different to report in the model.

In the spice we do below sweep ranges. While reporting we report back to -1.8V to 3.6V since the total range (5.4V is fixed for all corners irrespective of the abs voltage sweep).

Thanks
vinayak

________________________________
From: Lynne D. Green [mailto:lgreen22@mindspring.com]
Sent: Friday, June 10, 2011 1:19 PM
To: Ghatawade, Vinayak
Cc: ibis-users
Subject: Re: [IBIS-Users] IV clamp range

Hello, Vinayak,

You do not say which table exhibits a Crossing, or at what voltage.
- A clamp table can have a crossing for V<0 when the "clamping" is bipolar, while the drive is CMOS. Physically, bipolar and CMOS exhibit opposite dI/dTemp at fixed V. In this case, the total current may also have a crossing.
- A clamp table can exhibit a crossing due to numerical resolution when separating the clamp and drive currents into their respective tables. The total (summed) current usually does not show this type of crossing.
- It is rare to see I-V crossings in the range 0 to Vcc.

It is strongly recommended for all I-V tables to use the same voltage range (-Vcc to 2Vcc). In your example, that would be -1.8V to +3.6V.

As a model maker, you could submit a model to the IBIS Model Review Committee.
http://www.eda.org/ibis/home/support/support.htm

Cheers,
Lynne

Dr. Lynne Green
Chair, IBIS Model Review Committee

On 6/10/2011 12:00 AM, Ghatawade, Vinayak wrote:
Hello,

I have question reagarding the IV sweep ranges used for IBIS IV table generation.
Cookbook does not have detailed sweep range for all corners specified explicitly.
The reason that I am asking this question is we have IV table which has cross-overs for nom, strong and weak corners.
In spice I see this behavior which is expected as per diode behavior since the corners are temp variable as well.
Weak will turn on (125c) first and then followed by nom (25) and strong (-40c). This results in the crossover.
Some customers are not willing to have these crossover (not sure why?). But I feel since this is real behavior you should see the same
reflected in the ibis model.

Do you see a reason why IV crossovers are not allowed (recommended). I did not see any checklist or parser giving out any warning /error due this this.

Going back to the sweep voltage range when I see this crossover in spice (I sweep voltages as mentioned in cookbook) and report the strong, weak to fit in the
typical range voltage axis in the ibis model.

Ex 1.8V IO below is the numbers that I use for IV sweep range.

Sweep range that I use for typ
-1.8 to 3.6

Min/weak will be
-1.962 to 3.428

Max/strong will be
-1.602 to 3.798

Thanks
vinayak

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