Re: [IBIS-Users] Multi Power Buses IBIS models.


Subject: Re: [IBIS-Users] Multi Power Buses IBIS models.
From: John Phillippe (ra6314@email.sps.mot.com)
Date: Thu Aug 22 2002 - 07:02:56 PDT


Anshuli Goel wrote:
>
> Hi
>
> I am trying to generate the IBIS model for input model with multiple VDD
> and VSS supply.I have in by ckt 2 VDDs and 2VSS.One VDD operates at 3.3 and
> another at 1.8.The circuitry that is in direct contact with outside world
> is working at 3.3 Volt while other circuitry is working on 1.8 V . As there
> is no option to model these multi power buses in s2ibis2 utility . What
> should I do to eliminate this problem.?
>
> One more thing is Vinl and Vinh parameter must for input model to be
> supplied in s2ibis2 utility ?
>
> What is the difference in vinl,vinh and Vil and Vih . ? Where and how
> these parameters should be used ?
>
> If anybody can answer my querries that will be really helpful. ?
>
> Regards
> Anshuli Goel
> Texas Instruments
>
> ------------------------------------------------------------------------
>
> Subject: Multi Power Buses IBIS models.
> Date: Wed, 14 Aug 2002 15:12:06 +0530
> From: Anshuli Goel <anshuli@india.ti.com>
> Organization: Texas Instruments
> To: ibis-info@eda.org
>
> Hi
>
> I am trying to generate the IBIS model for input model with multiple VDD
> and VSS supply.I have in by ckt 2 VDDs and 2VSS.
> One VDD operates at 3.3 and another at 1.8
> As there is no option to model these multi power buses in s2ibis2
> utility . What should I do to eliminate this problem.?
>
> One more thing is Vinl and Vinh parameter must for input model to be
> supplied in s2ibis2 utility ?
>
> What is the difference in vinl,vinh and Vil and Vih . ? Where and how
> there parameters should be used ?
>
> In generating the models I am able to generate the GND clamp curve
> properly but in Power Clamp curve I am getting very low values of
> current . What could be the reason for this ?
>
> If anybody can answer my querries that will be really helpful.

Anshuli,
  I ran into this problem as well. What I did, was to use the higher
VDD, in your case 3.3V, in the .s2i file. Then in my library file, I
added the following spice command:

.global gnd vdd vss vddh
bvdd vdd gnd v=(0.52*v(vddh))

This generates 2.6V from the 5V VDD I'm using. My buffer uses VDDH=5.0V
externally, and VDD=2.6V internally.

-- 
John Phillippe
SPS, 32 Bit Embedded Controller Division, IC Creation
Motorola      -  512-895-1835
Austin, TX    -  ra6314@email.sps.mot.com
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