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Facility Grounding & Bonding Based on the EMC/PI/SI Model for a High
Speed PCB/Cabinet
William Bush (wbush@ieee.org)
Industry Consultant
PQ, EMC-PI/SI, Surge, G&B
PEG 2011 – Huntsville, ALApplying Protection to Traditional and Converged Networks
and: SILICON LABS AN203 PRINTED CIRCUIT BOARD DESIGN NOTESwww.silabs.com
Presentation Topics
• Emphasis on a high-level discussion
• The great divide: electrical vs.. electronic
• What are EMC-PI/SI and High Speed (HS)?
• EMC-PI/SI and HS model for a Cabinet/Rack
• EMC-PI/SI and HS model for a PCB
• Modern facility modeled via Cabinet/PCB
• Pros/cons to adapting Cabinet/PCB for facility
• What further work is needed??3/15/2011 - W Bush 2ATIS PEG 2011 Huntsville, AL
Emphasis on a high-level discussion
• Brief overview to indicate model applicability(?)– Stick figure – minimalist level
– Just the idea investigated
3/15/2011 - W Bush 3ATIS PEG 2011 Huntsville, AL
Traditional Facility Model
3/15/2011 - W Bush 4ATIS PEG 2011 Huntsville, AL
Wiring to Port(s)
Safety ground and
AC
Wiring and grounding evolves
with needs of a certain area
Structured wiring concept
should be applied for a modern
Facility - ANSI J-STD-607-A ?
AC & DC
The great divide: electrical vs. electronic
• Facility uses electrical basis – AC power– Electrical power engineers
– Very low frequency distribution; power via Volts
– Power quality and power systems compatibility
– Various comm links including high speed data
• Cabinet/PCB uses electronic basis - DC power– Electronic circuit engineers
– Higher frequency distribution; power via Amps
– High speed data links (TLines) on interconnects, board, package, chip, IC
3/15/2011 - W Bush 5ATIS PEG 2011 Huntsville, AL
The great divide: electrical vs. electronic 2
• Same series circuit – power source/return-path to load utilization (power to information) – via 2 bases – return path involves grounding
• Each basis describes the series circuit differently!!
3/15/2011 - W Bush 6ATIS PEG 2011 Huntsville, AL
AC basis DC basis
What are EMC-PI/SI & High Speed (HS)?
• EMC-PI/SI– Electromagnetic compatibility (EMC)
• Control of emissions and susceptibility at various frequencies
– Power Integrity (PI)• Control of DC power generation and distribution on a
PCB and its components; affects EMC and SI
– Signal Integrity (SI)• Control of signal distribution on interconnects
and drivers, receivers, links
• EMC and SI presented at PEG 2010 (Bush)3/15/2011 - W Bush 7ATIS PEG 2011 Huntsville, AL
• High Speed (HS)– Digital data at high mps
• High clock and data rate frequencies
• Fast rise/fall time of clock and data edges
• Typical PCB interconnects quickly approach and exceed electrical length
• PCB interconnects require characterization as a transmission line
• Can even apply at IC level as wiring may be 2 or 3 times longer than the electrical length
• PCB power distribution operates as a transmission line
3/15/2011 - W Bush 8ATIS PEG 2011 Huntsville, AL
What are EMC-PI/SI & High Speed (HS)? 2
EMC-PI/SI & HS model for Cabinet/Rack
• Cabinet/rack can transition the AC to DC basis or electrical to electronic domains– Typical cabinet/rack approaches EMC radiation
mode – concern is for higher than 30 MHz either by direct clock frequency or clock edge rates
– May be required to provide RF shielding via faraday cage effect and RF grounding/bonding
– Requires electrical safety grounding
– Likely requires equipotential bonding to adjacent metallics (mesh-BN)
3/15/2011 - W Bush 9ATIS PEG 2011 Huntsville, AL
• Cabinet/rack can transition the AC to DC basis or electrical to electronic domains– Requires EMI filtering on power and signal ports
– Requires ports to be RF grounded at chassis where port entry is located
– Desirable to locate ALL ports at ONE entry locale• Common RF reference and common bonding act to
effect a common-mode choke
• Shorts out common-mode voltage sources within PCB to the port reference so port external wiring does notradiate – only takes few micro-amps of RF to fail FCC!
3/15/2011 - W Bush 10ATIS PEG 2011 Huntsville, AL
EMC-PI/SI & HS model for Cabinet/Rack 2
• Cabinet/rack can transition the AC to DC basis or electrical to electronic domains– Rack power conversion and distribution
• Fusing, control, converters, inverters, wiring and termination, and routing – power, return, fault path
– Shelf power input and conversion and isolation
– Shelf power distribution to PCB slots and backplanes
– Rack and shelf power distribution requires differential power delivery and fault clearing
3/15/2011 - W Bush 11ATIS PEG 2011 Huntsville, AL
EMC-PI/SI & HS model for Cabinet/Rack 3
3/15/2011 - W Bush 12ATIS PEG 2011 Huntsville, AL
Preferred Model
Wiring to Port(s)
RF grounding and mesh-BN bonding (geometry not shown)
Safety ground and
AC
DC
DC
Optional bonding mat (Supplementary Bonding Grid)
EMC-PI/SI & HS model for Cabinet/Rack 4
Example PCB layout (credit:www.elmac.co.uk)
3/15/2011 - W Bush 13ATIS PEG 2011 Huntsville, AL
EMC-PI/SI & HS model for a PCB
• Ports confined (??) to plug-in card connector
• Voltage regulator modules (VRM) distributed on-board – power distribution decoupling
• Multilayer board construction– Allows for distribution of power, ground and
signal planes
• Signal interconnects modeled to show 3D current density (Maxwell full wave equations)
• Frequency and time domain characterization3/15/2011 - W Bush 14ATIS PEG 2011 Huntsville, AL
• PI characterized to minimize/control component and cavity resonance and enhance decoupling at device power port
• PI characterized even to IC level
• PI characterized for effect on SI
• Transmission lines characterized (SI and PI)
• Digital and analog domains controlled
• EMC filtering at ports
• Radiated emissions controlled
3/15/2011 - W Bush 15ATIS PEG 2011 Huntsville, AL
EMC-PI/SI & HS model for a PCB 2
• Clocks and data lines operated to the lower acceptable rate/speed – minimize EMI
• PCB layout carefully controlled to ensure constant impedance paths to maintain PI/SI
• Power and ground plane stitching
• Split planes to be avoided
• Possible on-board shielding structures
• Separation of “differences in magnitude”– Exp: High switching Amps and low analog signals
3/15/2011 - W Bush 16ATIS PEG 2011 Huntsville, AL
EMC-PI/SI & HS model for a PCB 3
Modern facility modeled via Cabinet/PCB
3/15/2011 - W Bush 17ATIS PEG 2011 Huntsville, AL
Safety ground
Wiring to Port(s)
ACAC or DC
Common-mode choke effect
CBN
mesh-BN
Structured wiring concept
should be applied for a modern
Facility - ANSI J-STD-607-A ?
Modern facility modeled via Cabinet/PCB 2
3/15/2011 - W Bush 18ATIS PEG 2011 Huntsville, AL
Zonal
concept
ONE entry/exit port!
Pros for adapting Cabinet/PCB to facility
• Falls fairly in-line with IEC zonal concept for EMC and meets present ATIS, TIA and IEEE stds intent
• Requires careful attention to power and signal differential delivery and common mode control – greatly enhances circuit performance and reduces EMI!
• Applicable to AC, DC or both at any location
• Provides a common bridge between electrical and electronic disciplines – & engineer speak
3/15/2011 - W Bush 19ATIS PEG 2011 Huntsville, AL
• Readily accommodates shielding practices
• Acclimates engineers to the same circuit topology whether electrical or electronic
• Promotes power and signal decoupling and isolation across voltage defined boundaries
• Brings electrical engineers into PI and SI arena
• Brings electronic engineers into power quality and system cabling arena
3/15/2011 - W Bush 20ATIS PEG 2011 Huntsville, AL
Pros for adapting Cabinet/PCB to facility
Cons for adopting Cabinet/PCB to facility
• Brings electrical engineers into “Maxwell’s World” extended beyond lumped circuits
• Electronic engineers seemingly content to be divorced from facility issues
• Growth of optical ports reduces issue of common-mode control
• Impacts facility design for disaster avoidance where diverse entries are desirable
• Product immunity (markets) has already decreased performance and damage incidents
3/15/2011 - W Bush 21ATIS PEG 2011 Huntsville, AL
What further work is needed??
• Engineering paper developed to present information from overview to detailed analysis for industry review/tutorial– Electrical and electronic sectors
• Diagrams, waveforms, models and simulations
3/15/2011 - W Bush 22ATIS PEG 2011 Huntsville, AL
Recommended References
• Electromagnetic Compatibility Engineering– Henry Ott – Wiley Books
• A Handbook of Black Magic– Johnson and Graham– Prentice Hall
• Electromagnetics for High-Speed Analog and Digital Communication Circuits– Ali Niknejad - Cambridge
• Guide on EMC in Power Plants and Substations– cigre Working Group 36.04
3/15/2011 - W Bush 23ATIS PEG 2011 Huntsville, AL
On the lighter side:The perils of an idea
3/15/2011 - W Bush 24ATIS PEG 2011 Huntsville, AL
“Mr. Madison (Bush), what you have just said, is one of
the most insanely idiotic things I have ever heard.
At no point during your rambling, incoherent response
(preso), were you even close to anything that could
have been considered a rational thought.
Everyone in this room is now dumber having listened
to it. I award you no points, and may God have mercy
on your soul.”
Adopted from the movie Billy Madison
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