RE: [IBIS-Users] Warning - "Typical value never becomes zero"

From: Tom Dagostino <tom_at_.....> Date: Mon Jul 11 2005 - 11:05:12 PDT · This archive was generated by hypermail 2.1.8 : Mon Jul 11 2005 - 11:06:12 PDT

Lynne

If there is a pulldown resistor or some other device that is sinking current
to some other voltage then the current in the powerclamp table will not be 0
current at 0.00 Volts.  True, a pulldown should be included in the
groundclamp but we don't know enough about this buffer to know what has
happened in it.  Is there a termination to some intermediate voltage?  We
don't know.  The model maker needs to determine the cause of this current
before anyone can say if this current is a problem or not.  The engineering
must be done first then conclusions can be drawn, not the other way around.

Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
tom@teraspeed.com
www.teraspeed.com

Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827

-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
Behalf Of Lynne D. Green
Sent: Monday, July 11, 2005 10:25 AM
To: 'Vivek Kumar Sundriyal'; ibis-users@eda.org
Subject: RE: [IBIS-Users] Warning - "Typical value never becomes zero"

Hello, Vivek,

Yes, this is serious.  Simulation symptoms could include DC
convergence failure and/or transient convergence failure.

Consider this circuit:
<I/O pin> - <resistor> - <PowerRef>

When the voltage at the I/O pin is the same as PowerRef, there is 0.000V
across the resistor. The resistor current is thus 0.0A.  However, your clamp
table says that 0.3193mA is flowing under this condition.  In this case, the
two currents are not equal, and KCL is violated.

Best things to check are [Power Ref] and [Power Clamp Ref].  One could
also check SPICE tolerance options to make sure they are not too large.

Best regards,
Lynne

"IBIS training when you need it, where you need it."

Dr. Lynne Green
Green Streak Programs
http://www.greenstreakprograms.com
425-788-0412
lgreen22@mindspring.com

-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf
Of Vivek Kumar Sundriyal
Sent: Monday, July 11, 2005 5:10 AM
To: ibis-users@eda.org
Subject: [IBIS-Users] Warning - "Typical value never becomes zero"

Hi ,

I have developed the IBIS model using s2ibis3 and I am using IBIS version
3.2

When I compile the .ibs file, I get the following warning  :

WARNING -
    Model MODEL1: POWER Clamp : Typical value never becomes zero WARNING -
    Model MODEL1: POWER Clamp : Minimum value never becomes zero WARNING -
    Model MODEL1: POWER Clamp : Maximum value never becomes zero

On looking at the Power clamp data, the current values that I get at 0.0V
are :
0.3193mA      72.3000uA      0.6643mA
for typ,min and max respectively.

Can anyone elaborate on this warning ?

And how serious is this ?

Cheers ,

Vivek

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