Subject: [IBIS-Users] RE: [IBIS] IBIS generation w/ two power supplies
From: Muranyi, Arpad (arpad.muranyi@intel.com)
Date: Fri Apr 25 2003 - 10:05:11 PDT
Wil,
If your "main power supply" is basically the core voltage of
your chip, then you don't need to mention it in the IBIS model.
IBIS only cares about the I/O supply voltage(s). In other words,
you only need to define those voltages in IBIS to which the
pullup, puldown and the clamp devices are connected in the
circuit.
Arpad
=================================================================
-----Original Message-----
From: Wil Ngan [mailto:wngan@idt.com]
Sent: Friday, April 25, 2003 9:55 AM
To: Muranyi, Arpad
Cc: ibis@eda.org; ibis-users@eda.org; ibis-info@eda.org
Subject: Re: [IBIS] IBIS generation w/ two power supplies
Arpad,
I could set [Pullup reference] to 3.3v or 5v, but with what
parameter do I set the main power supply at 5v? (in both
case)
Wil
"Muranyi, Arpad" wrote:
> Wil,
>
> It sounds that your pullup's reference voltage is programmable,
> correct?
>
> In that case, you should use the model selector and make two
> models, on with [Pullup Reference] = 3.3 V, and the other with
> [Pullup Reference] = 5 V.
>
> Arpad Muranyi
> Intel Corporation
> =============================================================
>
> -----Original Message-----
> From: Wil Ngan [mailto:wngan@idt.com]
> Sent: Thursday, April 24, 2003 4:54 PM
> To: ibis@eda.org; ibis-users@eda.org; ibis-info@eda.org
> Subject: [IBIS] IBIS generation w/ two power supplies
>
> hi,
>
> I'm trying to generate an ibis file from a circuit with two power
> supplies, vcc and vccq. Vcc is fixed at 5v, while vccq is either 3.3 or
> 5v, depending on what we would like the output high to be. How do I
> going about doing this?
>
> In the past, I've used [Pullup reference], [Power clamp reference] to
> set vcc to 5v, vccq to 3.3v, respectively. However, I just realized
> that I cannot set vccq using [power clamp reference], since there's
> actually NO power clamp in my circuit. (The ckt only has ground clamp
> transistors, which protects the device from overly low input voltages,
> at same time, that same device works to protect high input voltages
> through breakdown.) I
> had been generating [Power clamp] current table while in fact there is
> no power clamp circuit. Not good. Furthermore, this causes [Pullup]
> current table to be wrong, since [Pullup]currents = I(pullup generated
> by hspice) - I(power clamp), so the numbers in my [Pullup] table are
> actually lower than they should be.
>
> So, going back to the original question, without using [Pullup
> reference] or
>
> [Power clamp reference], how should I go about in providing two power
> supplies to this circuit to generate ibis file?
>
> - Wil
> idt sram, 408/330-1623.
>
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