Subject: RE: [IBIS-Users] Ramp and Rising waveform Load
From: Muranyi, Arpad (arpad.muranyi@intel.com)
Date: Thu Jan 16 2003 - 08:20:01 PST
Anshuli,
You should use an R_fixture around 50 Ohms, not 500. The best
value for R_fixture is the transmission line impedance that
the buffer is designed to drive. This is usually in the range
below 100 Ohms.
I don't have the time to explain it now, but if you have
waveforms which go almost rail to rail, you do not have a
very good IBIS model.
Arpad Muranyi
Intel Coproration
==============================================================
-----Original Message-----
From: Anshuli Goel [mailto:anshuli@india.ti.com]
Sent: Thursday, January 16, 2003 5:05 AM
To: 'ibis-users@eda.org'
Subject: [IBIS-Users] Ramp and Rising waveform Load
Hello IBIS Gurus
While generating IBIS model I use 50 ohm as rload for calculation of
Ramp rate.
Should my rising and falling waveform also be generated for same load
fixture. ?
If I use 50 ohm as load fixture for rising and falling waveform ,the
voltage level in rising and falling waveform reaches only to maybe 50 %
of VDD.But when I use some high resistance as 500 ohm for load fixture
for rising and falling waveform (keeping Rload for ramp rate still as 50
ohm ) gives me waveform reaching to VDD. What is the best way to get
both ramp rate and rising and falling waveform ..
What significance does this Rload ( for ramp rate ) and R_fixture ( For
waveforms) hold ?
In case of simple I/O buffer what both these parameters define if
I think of physical entity of package and board ? What is the mean of
test structure the buffer is supposed to see ?
Regards
Anshuli
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