Facility Grounding & Bonding Based on the EMC/PI/SI Model for a High Speed PCB/Cabinet

Transcription

1 Facility Grounding & Bonding Based on the EMC/PI/SI Model for a High Speed PCB/Cabinet and: SILICON LABS AN203 PRINTED CIRCUIT BOARD DESIGN NOTES William Bush (wbush@ieee.org) Industry Consultant PQ, EMC-PI/SI, Surge, G&B PEG 2011 Huntsville, AL Applying Protection to Traditional and Converged Networks

2 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/ W Bush ATIS PEG 2011 Huntsville, AL 2

3 Emphasis on a high-level discussion Brief overview to indicate model applicability(?) Stick figure minimalist level Just the idea investigated 3

4 Traditional Facility Model 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 Safety ground and Wiring to Port(s) AC & DC 4

5 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 5

6 The great divide: electrical vs. electronic 2 Same series circuit power source/returnpath to load utilization (power to information) via 2 bases return path involves grounding Each basis describes the series circuit differently!! AC basis DC basis 6

7 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) 7

8 What are EMC-PI/SI & High Speed (HS)? 2 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 8

9 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) 9

10 EMC-PI/SI & HS model for Cabinet/Rack 2 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 not radiate only takes few micro-amps of RF to fail FCC! 10

11 EMC-PI/SI & HS model for Cabinet/Rack 3 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 11

12 EMC-PI/SI & HS model for Cabinet/Rack 4 Preferred Model DC Safety ground and Wiring to Port(s) DC AC RF grounding and mesh-bn bonding (geometry not shown) Optional bonding mat (Supplementary Bonding Grid) 12

13 Example PCB layout (credit: 13

14 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 characterization 14

15 EMC-PI/SI & HS model for a PCB 2 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 15

16 EMC-PI/SI & HS model for a PCB 3 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 16

17 Modern facility modeled via Cabinet/PCB Common-mode choke effect AC Safety ground Wiring to Port(s) AC or DC Structured wiring concept should be applied for a modern Facility - ANSI J-STD-607-A? CBN mesh-bn 17

18 Modern facility modeled via Cabinet/PCB 2 Zonal concept ONE entry/exit port! 18

19 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 19

20 Pros for adapting Cabinet/PCB to facility 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 20

21 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 21

22 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 22

23 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

24 On the lighter side: The perils of an idea Adopted from the movie Billy Madison 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. 24