Re: [IBIS-Users] IV clamp range

I concur with Arpad. The IBIS Quality 2.0 spec mentions this briefly:

5.3.1. {LEVEL 2} I-V tables have correct typ/min/max order

Inspect every I-V table. Check for proper order of the I-V tables. The order
of the column values in
the table must be:

VOLTAGE, Typical Current, Minimum Current, Maximum Current

In most cases the Maximum current should be greater than the Typical
current, which should be
greater than the Minimum current, in the active region (e.g., where device
is not clamping). The
most common exception is for compensated devices, where the Typical,
Minimum, and Maximum
curves may nearly overlay each other. Also, [POWER Clamp] curves may exhibit
crossovers due
to differences in the voltages at which clamping begins.

This check is easily accomplished by viewing the curves and checking
visually. Checking
combined curves is preferred, but checking of individual curves is
acceptable.

( http://www.eda.org/pub/ibis/quality_wip/)

My philosophy is that when it comes to models real behavior is always
acceptable :)

Mike

On 6/10/11 9:37 AM, "Arpad Muranyi" <Arpad_Muranyi@mentor.com> wrote:

> 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 doesn¹t
> 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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