RE: [IBIS-Users] IV clamp range

Vinyak,

The crossing you show is perfectly normal. The knee

voltage is determined by the P-N junction (parasitic

diode), and the slope is determined by the resistance

of the Silicon. These two have different dependencies

on corner conditions. In other words, the slope doesn't

get steeper when the knee voltage becomes smaller.

I hope this helps.

Arpad

=========================================================

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of Ghatawade, Vinayak
Sent: Friday, June 10, 2011 3:22 AM
To: Lynne D. Green
Cc: ibis-users
Subject: 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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