RE: [IBIS-Users] IV Curves

Hi all,
Thanks for the answers, i appreciate them very much.
I am sorry to say that i am poor in SI, i couldn't get how the reflection
for an open circuit transmission with coefficient=1 cause the voltage at
driver site become -vcc (the reflection is the multiplication of voltage
(vcc) and coefficient (+1) which end up with +vcc)? I am sorry but could
someone shed some light to get rid of my confusion?
Much appreciated.

-Lee

>From: "Muranyi, Arpad" <arpad.muranyi@intel.com>
>To: <ibis-users@eda.org>
>Subject: RE: [IBIS-Users] IV Curves
>Date: Mon, 10 Jan 2005 08:58:27 -0800
>
>Just a couple of refinements to the answers I have seen
>so far.
>
>1) Actually none of the IV curves are GND relative any more,
>this is just a terminology that is left over from the first
>version of the IBIS specification.
>
>Note that all four IV curves now have an associated [*** Reference]
>keyword, which defines the voltage for the origin of the IV curve.
>Therefore a pulldown IV curve for an RS232 driver could be referenced
>to -12 V, for example, which is not GND relative by any means...
>It is true, in most cases we reference the pulldown and GND clamp IV
>curves to 0 V, so it is easy to forget about this capability.
>
>2) Lynne said it right, but I would like to add, that even if you
>have a perfect open at the end of the T-line, the 2Vcc or -Vcc
>doubling will only happen if your driver is superconductive,
>i.e. very low impedance. This is because the T-line voltage
>doubling doubles the incident step, which is determined by the
>voltage division based on the T-line impedance, and the driver
>impedance. So the 2Vcc and -Vcc voltages are kind of an absolute
>maximum condition which will most likely never happen.
>
>Arpad Muranyi
>Intel Coproation
>====================================================================
>
>
>-----Original Message-----
>From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf
>Of lgreen
>Sent: Monday, January 10, 2005 8:43 AM
>To: 'lee yang'; ibis-users@eda.org
>Subject: RE: [IBIS-Users] IV Curves
>
>Hello, Lee,
>Please see answers inserted.
>- Lynne
>
>-----Original Message-----
>From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf
>Of lee yang
>Sent: Sunday, January 09, 2005 5:58 PM
>To: ibis-users@eda.org
>Subject: [IBIS-Users] IV Curves
>
>Hi IBIS experts:
>
>I have a few questions regarding IBIS data:
>1) What is the reason of ground clamp and pulldown data is ground relative
>while power clamp and pullup data is vcc relative?
>-- This was an arbitrary decision made in the IBIS 1.0 specification.
>Note that GND-and Pulldown tables currents shift relative to ground
>(and currents usually go through 0A at GND), while Power- and Pullup tables
>shift when Vcc changes (and currents usually go through 0A at Vcc).
>
>2) The IV curves data is covered from -vcc to 2vcc, in what condition the
>voltage would become -vcc? (eg1: output is driving vcc and the receiver end
>is being shorted, the reflection coefficient is -1, then the maximum
>negative voltage is 0V (vcc + (-1*vcc)=0); eg2: output is driving 0v and
>the
>
>reciever end is being shorted, the reflection coefficient is -1 as well,
>would it be any reflection if the output is driving 0V with reciever end
>being shorted to ground?)
>-- A load with a small capacitance has a reflection coefficient close to
>+1.
>For an open circuit termination, the reflection coefficient is +1.
>A rising waveform into an "open circuit" load can cause 2*Vcc at the
>driver,
>and a falling reflection (starting at Vcc) can cause -Vcc at the driver.
>
>
>Hope you all could shed some light here.
>Thanks.
>
>Yours Faithfully,
>LY
>
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Received on Tue Jan 11 17:11:02 2005