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

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Traditional Facility Model

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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

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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!!

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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

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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)

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• 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!

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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

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EMC-PI/SI & HS model for Cabinet/Rack 3

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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)

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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

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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

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EMC-PI/SI & HS model for a PCB 3

Modern facility modeled via Cabinet/PCB

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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

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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

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• 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

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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

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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

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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

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On the lighter side:The perils of an idea

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“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