what makes a better i/o driver model?
DESCRIPTION
What Makes a Better I/O Driver Model?. Vadim Heyfitch Cadence Design Systems, Inc. (978) 446-6455 [email protected]. Content: What are we going to discuss?. Personal Introduction What is the intended audience? Who should care? What is an IBIS Driver model? Why verify? - PowerPoint PPT PresentationTRANSCRIPT
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What Makes a Better I/O Driver Model?
Vadim HeyfitchCadence Design Systems, Inc.
(978) [email protected]
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Content: What are we going to discuss?
• Personal Introduction
• What is the intended audience? Who should care?
• What is an IBIS Driver model?
• Why verify?
• Model Integrity (MI) - Cadence Tool for verification, editing– What can it do?
• What to watch out for: typical problems? – Qualitative criteria of IBIS model “goodness”
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What is an IBIS Driver model?
IBIS
Pull-Down
I-V
Pull-Up
I-V
PWR_Clamp
I-V
GND_Clamp
I-V
Pkg
C_comp
V-T
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Why verify?
• IBIS speed ~>25x of SPICE lends it for solution space exploration (aka pre-layout analysis)
• Time spent upfront pays off
• Lots of bad IBIS models out there– Only 42% passed IBISchk3 without errors or warning
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Model Integrity (MI) Module - a graphical look at IBIS
models
‘Like reading ASCII files?
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Model Integrity (MI) Module – What Can It Do?
• Ibischk3 Golden Parser: GUI to navigate errors and warnings.• Visual representation and navigation of (multiple) .ibs file
structure• Editing, Sorting, …• Translation to:
– IBIS to DML
– QUAD to DML
– Espice to Spice
• Viewing curves– V-I for Pullup and Pulldown, GND_Clamp, PWR_Clamp
– V-T
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Look and Feel (Physical View)
Error(s)
Warnings(s)
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Look and Feel (Object View)
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Navigating Errors and Warning
Click on warning message
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Viewing Curves
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Viewing Curves (cont’d)
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What should we do to insure quality of the next IBIS model
we use in simulation?
• Check original data:1. all I-V curves (i.e., static behavior):
V-Range of I-V data: - Vcc <> + 2Vcc Pulldown I-V WITHOUT GND_clamp Pullup I-V WITHOUT PWR_clamp GND_clamp PWR_clamp
2. V-T (i.e., dynamic behavior): How many V-T curves? None, 2, 4? V-T does not contradict I-V ? dV/dT_r/f (even if V-T available)
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Pullup and PWR_clamp – translating the raw data
Vcc 2Vcc-Vcc
I
Vcc 2Vcc-Vcc
IV table = Vcc – V raw
V raw
V table
PU
PC
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Qualitatively Correct I-V Picture
Vcc 2Vcc-Vcc
I
V
PU
PD
PWR
GND
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Error: Clamp Diode Current – not subtracted
What’s wrong with this picture?
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Clamp Diode Current – properly subtracted
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PVT variation
Vcc 2Vcc-Vcc
I
V
Slow
Typical
Fast
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All I-V info at once- textbook example
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Suspiciously Looking Model
+ Vcc
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V-T: dynamic behavior
[Ramp]| variable typ min maxdV/dt_r 1.518V/360.974ps 1.260V/534.096ps 1.731V/327.019psdV/dt_f 1.759V/167.287ps 1.579V/534.096ps 1.928V/155.338psR_load = 50.0000
Required:
80%
20%
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V-T
DC levels must correlate to I-V curves
Optional:
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Driving in to Configurable Load
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What do simulators do with an IBIS model?
• Simulator specific
• If 4 V-T available (Rising and Falling w/f into pull-up and pull-down R_fixture) – it’s the best! Can extrapolate between I-V curves.
• Read the last two papers listed in references.
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Sources of useful info
• Papers to read:– “Assessing and Improving the Quality of IBIS models”,
SiSoft, Inc.– “IBIS Behavioral Models”, Micron’s Technical Note TN-00-07.– “Correlating IBIS and Hspice Buffer Models”, Todd Westerhoff,
CISCO Systems.– “A Critique of IBIS Models Available For Download on the Web:
Part 1”, SiQual Inc., Jan. 22, 2002.– “Introduction to IBIS Modeling of Fiber Optic Transceivers”, Mark
Chang, Agilent Technologies.– “Extraction of Transient Behavioral Model of Digital I/O Buffers from
IBIS”, P.F.Tehrani, Y.Chen, J.Fang, 1996.– “The Development of Analog SPICE Behavioral Model Based on IBIS
Model”, Y.Wang, H.N.Tan, 1999.
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What have we talked about today?
• What is an IBIS Driver model?• Why verify? • Model Integrity (MI) - Cadence Tool for verification,
editing– What can it do?
• What to watch out for: typical problems? – Qualitative criteria of IBIS model “goodness”
• Pointed to sources for further reading