Subject: [IBIS-Users] FW: IBIS Modeling Clarification
From: John Angulo (jangulo@innoveda.com)
Date: Tue Jun 11 2002 - 10:57:03 PDT
The following is posted on behalf of Andris Lauzums. Please send all
private replies to alauzums@intersil.com.
-------------------------------------
Hello. I am currently constructing an IBIS model for a RS-485 Differential
Output transceiver. This is my first attempt at IBIS modeling, and I am
uncertain about what values to specify for certain [model] parameters.
I am attempting to extract rising and falling waveform data on a bench using
a Tektronics TDS-3040 (300MHZ 2.5GS/s ....The 300mHZ bandwidth does not
seem to be limiting my rise and fall time readings) along with a 10X 8.7pF
test probe and a HP 8131A Pulse Generator. My test board is a copper-clad
type breadboard that does not seem to adversely affect my AC test readings.
The model type is an RECEIVER/DRIVER_BI I/O (Driver output, Receiver Input)
I am uncertain about what Vinh, Vinl, Vmeas, Cref, Rref, and Vref parameters
to specify.
The datasheet specifies high and low Voltage input thresholds at 0.8V, and
2.0V....Do i use these values for Vinh, and Vinl? What high and low input
voltages do I set on my pulse generator?
Is the Vmeas parameter the delta between Vinh and Vin? What is this
"Reference Voltage for timing Measurements"?
What do i specify for my Cref value? My board has 12.5pF of capacitance
betewwn my I/O pin and GND. Do i use my board capacitance value? I not
using any caps from my I/O pin to GND
I terminated my differential output pins with a 54.9 ohm resistor. Is this
the R_ref, R_load, or R_fixture value that i need to specify?
Is my V_fixture value the same as my V_meas as well?
What do i specify for C_fixture and L_fixture?
In other words:
I am trying to figure out what values to include for the following
parameters:
Vinh
Vinl
Vmeas
Cref
Rref
Rload
Rfixture
Vfixture
Cfixture
Lifixture
I have read through the various articles on the ANSI/EIA-656-A Homepage. It
has proved to be a great source of information, although because of my
unfamillarity with IBIS, it has left me unclear on the problems that I
describe above. I would appreciate any assistance that can be provided. I
can be reached at (321) 729-4811. I hope this forum can help me get my
project underway.
Thanks,
Andris Lauzums
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