RE: [IBIS-Users] "Frequency Dependant IBIS Models"

Hello,  Radovan,

Frequency dependent models are used for passive interconnects (such as
transmission lines).  They are not  used for I/O buffers.

[Ramp] values are not used during simulation when V-t tables are provided.
Since many SI tools use [Ramp] values for pre-simulation calculations, valid
[Ramp] data is still needed.

Removing points at the end of V-t tables when V is no longer changing is
helpful with simulators that require simulating to the end of the table
before the buffer can toggle.  This does not help the "over-clocking"
problem where the buffer must toggle before the voltage has settled.  IBIS
does not define how a simulator should handle over-clocking, so different
simulators can handle this differently (invalid simulation output, crashing,
etc.).

I hope this information has been helpful.

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 Radovan.Vuletic@infineon.com
Sent: Monday, June 20, 2005 9:51 AM
To: ibis-users@eda.org
Subject: [IBIS-Users] "Frequency Dependant IBIS Models"

Hi IBIS Experts,

question about so called "Frequency Dependant IBIS Models".

I understand  why are these things happen (if rising +  falling waveforms on
V/T are longer than your clock period), but I still don't know what are
simulators doing with V/T curves and dV/dt_r and dV/dt_f? 

I have seen some models where are the trailing points, i.e. points when the
rising/falling has finished and response has steady state commented out (or
deleted), at it is fine. But, I have also seen some models where are the
points with no current change before signal even started to rise/fall
deleted, so this V/t curves are artificially made to fit in duty-cycle. That
means that fly-by-time (propagation of signal from I/O buffer input to I/O
buffer output) of an I/O buffer is reduced to almost zero? Is it OK to do
something like that? I don't know what are simulator doing with V/t curves,
but on that way fly-by information is lost! Is it needed at all?

If one can delete trailing points or points with no current change and
present that as an valid model, do we need then V/t curves at all? Then
should be only dV/dt_r,f data enough...Right or I am missing something?

I would be thankful for any kind of answer or link where are these things
explained.

Best regards / Mit freundlichen Grüßen / S poštovanjem Radovan Vuletić

Infineon Technologies AG
MP PD PDE
Room 03.911
Balanstraße 73
D-81541 München

Phone:		+49 (0)89 234 20108
Fax:		+49 (0)89 234 27705
Fax (PC):	+49 (0)89 234 955 5305 

E-mail: radovan.vuletic@infineon.com

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