Subject: dv/dt measurement

From: Stephen Peters <[email-masked]>
Date: Wed, 18 Jun 1997 14:33:34 -0700

Hello Vincent:

   Good question, and I will attempt to clarify the cookbook.

   The purpose of the rise and fall data is to give the
simulator information on the devices' pullup and pulldown
transistors turn-on/turn-off times.  This data should not include any 
degredation of rise/fall time due to packaging effects.
In a simulation environment generating the 'transistor only' data is not
a problem -- simply remove the package from the simualtion. Unfortunetly,
in a measurement environment one cannot remove the package and so
any data gathered will include package effects.  What the model maker must
do in that case is as described in the cookbook: 

"Using the known packaging parameters and measured I-V curves, construct 
a simulation model of the device using a best guess of the rise/fall time.  With 
an IBIS simulator, adjust the rise/fall times in the model until the simulation 
results match the oscilloscope waveforms."

  Note that in either case (simulation or measurment) do NOT include a
load capacitor on the output.  Adding a load capacitor only complicates
things.

          Regards,
          Stephen Peters
          Intel Corp.

all,

I have a question on rise and fall measurement.
In the cook book, it states that the rise and fall time
measurement are "no load" measurements; ie, remove the 
package parameters(L/R/C) before doing the simulation.

But, later in Lab measurement section, it states that
Capturing rise/fall time data requires either a specific test 
fixture or a motherboard to which the DUT can be attached. 
Rise/fall time measurements require an oscilloscope with 
at least a 4 GHz bandwidth. Take into account the effect 
on the rise/fall times of the device packaging and capacitive 
load.

So, why it does not use any C_pkg and C_leadfram vaule
in rise and fall time measurement in IBIS model.

I am generating ibis model from spice.

-- 
Best Regards,

			Vincent Chang

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*  Vincent Chang                         TI MSG ID: hui8              *
*  Design Automation                     mailto:[email-masked]    *
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