Modeling On-Die Power Supply Decoupling - IBIS · Conclusions • A complete model for on-die power...
Transcript of Modeling On-Die Power Supply Decoupling - IBIS · Conclusions • A complete model for on-die power...
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Modeling On-Die Power Supply DecouplingRandy Wolff – Micron TechnologyLance Wang – IO Methodologyg gy
DesignCon IBIS SummitSanta Clara, CA, USA
February 2, 2012
©2012 Micron Technology, Inc. All rights reserved. Products are warranted only to meet Micron’s production data sheet specifications. Information, products, and/or specifications are subject to change without notice. All information is provided on an “AS IS” basis without warranties of any kind. Dates are estimates only. Drawings are not to scale. Micron and the Micron logo are trademarks of Micron Technology, Inc. All other trademarks are the property of their respective owners.
©2012 Micron Technology, Inc. | 1February 2, 2012
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Outline
• Elements of an IBIS 5.0 model for Power Integrity simulationsimulation
• On-die power supply decoupling models
Parasitic vs. non-parasitic
Optimization of models
• Simulation results - Transistor-level vs. IBIS 3.2, 5.0
• Conclusions
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IBIS 5.0 Power Integrity Modeling
• PI modeling requires [Composite Current], [ISSO PU], [ISSO PD] and a detailed model of decoupling capacitance[ ] p g p
ISSO PU
Decoupling
ISSO PD
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* Image from IBIS 5.1 Draft Specification
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Power Supply Decoupling Elements
Bond Pad Layout Floorplan
BBypass Cap
Parasitic
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Parasitic Decoupling
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Parasitic Decoupling Capacitance
14.0000
6 0000
8.0000
10.0000
12.0000
12 0000 14 0000
Capacitance
0.0000
2.0000
4.0000
6.0000 12.0000-14.0000
10.0000-12.0000
8.0000-10.0000
6.0000-8.0000
4.0000-6.0000
2.0000-4.0000
0.0000-2.0000
Note:• Strongly frequency dependant
W kl lt
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• Weakly voltage dependant
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Optimization of Parasitic Decoupling
~ 13.4pF - not insignificant
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Transistor-level vs. Model
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Optimization of All Decoupling
Adds ~450pF!
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Transistor-level vs. Model
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Simulation Setup• DDR3 DQ I/O buffer, 1.5V
• PRBS pattern, minimum bit width of 1.25ns
Typical corner
VCCQ
PKG
I_vccq
• Typical corner
• Various On-die decoupling capacitance models included as SPICE models50 ΩZo=50 Ω
PKG
PKG
DQ1
V_load
• DQ1 + DQ2 switching (with different PRBS patterns) with fully coupled SPICE package model
VTT3pF
PKGDQ1
DECAP
VTT
50 ΩZo=50 Ω
3pF
PKGDQ2
DECAP
VSSQ
PKG
DECAP
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VSSQ
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No Decoupling Model
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No Decoupling Model
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Parasitic Decoupling Model Included
Good match to ringing behavior
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Parasitic Decoupling Model Included
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All Decoupling Modeled
Ringing behavior no longer matches. Why?y
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All Decoupling Modeled
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Conclusions
• A complete model for on-die power supply decoupling must include models for parasitic caps and designed-in caps
• Simple, multi-stage RC circuits accurately model on-die decoupling circuits
• A method is needed for including complex decoupling models along with an IBIS 5.0 model
• More investigation needed to understand circumstances where IBIS 5.0 power-aware models do not match SPICE models
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May 31, 2011