Re: Do IBIS models support E

        Reply to: RE>Do IBIS models support EMI
10 db of difference at what frequency? One has to specify the freq when
you talk about the radiated power. I will have hard time to believe
that it was 10 db of difference from dc to optical freq.

Yes, the dc model will work as a first order approximation, (ofcourse,
dc model is the primary requirement to represent a device), but will
not have anywhere close to accurate radiation power AS A FUNCTION OF
FREQ.

Kelle has brought a very good point, as one uses the appropriate
terminations and accounts for signal integrity issues, EMI will be less
compared to when signal integrity issues are not accounted for.
Unterminated Xlines, open eneded Xlines- long stubs etc.,
discontinuties- all act as antenna at one freq. or the other. However,
that gives a feel of comfort, not the quantitative measure of how much
less radiations.

In the present model we are considering for IBIS with dc IV
characterisitcs, intrinsic device (without package) will have the gain
with respect to frequency from dc to optical freq.- if that is true, it
means that when one calculates the ac currents through the
interconnects, the only reason those ac currents will be different is
due to the freq response of interconnects. As far active devices- i/o,
they will have the same freq response at all the freqs. Well, an
analogous situation is, if the i/o models do not change with voltage
i.e. we use only linear model- will that be acceptable? Practical
devices tend to have 3db gain bandwidth, which define their usefulness
for a particular high speed or high frequency application. ECL bipolar
devices may have 3db gain bandwidth in x00 MHz- x GHz range, state of
the art bipolar devices have 3 db gain bandwidth in low 1x GHz range,
MESFET devices have typical useful freq response to high 1x GHz, and
HEMTs go upto xx GHz. If we model all devices with their IV models only
and not worry about their freq response, we are assuming that intrinsic
devices have same freq response (dc to infinity). In essence, given the
same IV dc model for all devices (CMOS, ECL, BiCMOS, MESFET, HEMT)- for
the sake of discussion), CMOS devices typically have lowest freq
response, will not be able to sustain any signal above x00 MHz, so
there will be minimal signal strength supported by the device at higher
freqs, whereas if one is using MESFETs, the system may be able to
support signals at much higher freqs and hence may have significant
radiated power at higher freqs.

Yes, the package parasitics will limit the freq response of the device,
but in case one uses unpackaged device, devices will have freq response
to infinite. Also, whether one puts an ECL- bipolar device or a MESFET
device or for the sake of argument a HEMT device, all will have the
same freq reponse (may have differences due to dc IV models, but freq
response will be the same)- no effect on radiated power pattern as a
function of freq as calculated by the EMI tool.

Ravender
--------------------------------------
Date: 1/11/94 8:20 PM
To: Ravender Goyal
From: Kellee Crisafulli
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Date: 11 Jan 94 23:10:33 EST
From: Kellee Crisafulli <71436.1314@CompuServe.COM>
To: IBIS ALL <ibis@vhdl.org>
Subject: Do IBIS models support EMI simulations?
Message-Id: <940112041032_71436.1314_BHU37-1@CompuServe.COM>

From: Kellee Crisafulli, HyperLynx

I believe that IBIS models will work for first order EMI simulations.
The
best indications that I have seen are when comparing the EMI profiles
from
a real system that has had the transmission lines terminated and the
same
system without termination, there can easily be more than 10 db of
difference.
Received on Wed Jan 12 09:02:05 1994