Grounding: The Grounds for EMC Design …

1 grounding : The Grounds for EMC Design1 grounding : The Grounds for EMC DesignElya B. JoffePresident, IEEE PSE SocietyPast President, IEEE EMC SocietyGrounding: The Grounds for EMC Design "Ground is where potatoes and carrots thrive"(Dr. Bruce Archambeault) grounding : The Grounds for EMC Design2 grounding in EMC Engineering grounding is probably of electrical /electronic systemdesign, often considered as "black magic Not easy to understand intuitively No straightforward definition, modeling or analysis Many uncontrolled factors affect its performance grounding forms an inseparable part of all electronic andelectrical designs, from circuit through system up toinstallation Design Implemented for EMC and ESD protection, for safety purposes, for lightning and surge protection.

2 The Grounds for EMC Design3 Parasitics in Passive Circuit ElementsParasite An organism that grows, feeds, andis sheltered on or in a different organismwhile contributing nothing to the survival of itshostGrounding: The Grounds for EMC Design4 Real World ResistorsRLSCP11 RSPZj Lj CR =+ + Frequency response of "Real World" (non-ideal) Resistors, (R=10 , LS=50nH and CP=1nF) 024681012110100 Frequency [MHz]Impedance [Ohm] grounding : The Grounds for EMC Design5 Real World CapacitorsCRS (ESR)LS (ESL)Rp11 CSSPZj L Rj CR =++ + Frequency response of "Real World" (non-ideal) Capacitors, (C=10nF, LS=5nH and RS=2m ) [MHz]Impedance [Ohms] grounding : The Grounds for EMC Design6 Real World InductorsRSLRpCp111 LPPSZj CR j L R =+++Frequency response of "Real World" (non-ideal) Inductors, (L=1 H, R=10m and CP=10pF) 1010010001000010100 Frequency [MHz]Impedance [Ohms] grounding : The Grounds for EMC Design7 Conclusions.

3 The Invisible Circuit Nothing is like it seems at At high frequencies, where performance of reactive components is most needed ( , for filters) - they may not perform as anticipated The INVISIBLE CIRCUIT must be considered in hi-speed circuit designGrounding: The Grounds for EMC Design8 Common Mode and Differential Mode SignalsGrounding: The Grounds for EMC Design9 Common- & Differential-Mode SignalsII IC=+1 22II ID= 1 22 IDIDdICICdID -Differential ModeCurrentIC -Common ModeCurrentExcellent flux cancellationNo flux cancellation Contradictions do not exist.

4 Whenever you think you are facing a contradiction, check your premises. You will find that one of them is wrong Atlas Shrugged grounding : The Grounds for EMC Design10 Sources of Common-Mode Signals Ground Loops External Radiated FieldOr Capacitive Crosstalk Electric FluxDrVin-2 ICMVG+IDM+ICM-IDM+ICMAI1I2I3 grounding : The Grounds for EMC Design11 Signal Propagation: Path of Least Impedance PrincipleFermat's principle leads to Snell's law; when the sines of the angles in the different media are in the same proportion as the propagation velocities, the time to get from P to Q is choose the easy way to cross hills In thermodynamics, the enthalpy or heat content is a quotient or description of thermodynamic potential of a system, which can be used to calculate the "useful" work obtainable from a closed thermodynamic system under constant pressure and entropy.

5 grounding : The Grounds for EMC Design12 One Rule to bring them alland in the darkness bind Ring to rule them all,One Ring to find them,One Ring to bring them alland in the darkness bind : The Grounds for EMC Design13 Path of Least Impedance Principle Visualize Return Currents Currents always To ground?? To battery negative?? Where are they? They are all flowing to their source!! All the rivers flow to the sea, but the sea is not full (Ecclesiastes 1:7) grounding : The Grounds for EMC Design14 Path of Least Impedance PrincipleElectrical Energy and electrical Potential In order to bring two like charges near each other or to separate two opposite charges work must be done Whenever work gets done, energy changes form As the monkey does work on the positive charge, he increases the energy of that charge The closer he brings it, the more electrical potential energy it has When he releases the charge.

6 Work gets done on the charge which changes its energy from electrical potential energy to kinetic energy Does the path the monkey travels with the charge make a difference? grounding : The Grounds for EMC Design15 Work done against an electric force in carrying a charge along a path from point a to b Electric Potential between with the points a and b:bbbaaaW F dl qE dl q E dl= = = ()work,or electric-energycharge movedbE a baWVE dlq = = = Furdluurdluura bb aW W = Path of Least Impedance PrincipleElectrical Energy and electrical Potential Does the path the monkey travelswith the charge make any difference?

7 Around a closed loop?()()0bb aE a bE a b aaVE dl V V V = = Right?In a lossless : The Grounds for EMC Design16 When time-varying magnetic fields are present it is not possible to describe the electric field simply in terms of a scalar potential V because the electric field is no longer conservative is path-dependent because: E 0 (Faraday's law of induction) Path of Least Impedance PrincipleElectrical Energy and electrical Potential In such cases we must consider the magnetic (vector) potential as well, and: Which remains conservativeCE dl Wrong!

8 !!AE Vt = urIn a lossless bb aW W = MFurbb aaE dl V V grounding : The Grounds for EMC Design17 Path of Least Impedance PrincipleWhich Path will the Return Current follow? Currents always take the path of least .. Distance? Resistance? Impedance!!! grounding : The Grounds for EMC Design18 Equivalent Circuit Path of Least Impedance Principle Which Path will the Return Current follow?or:-1()0S SSI R j L I j M + =SL M=1 SSSSI j LI R j L =+11,SgSSRI I I IL << >>SSgSRI IL >> >>In tightly coupled conductors:1C21Br2 Sdsr1I11Br2C1212dIV Ldt= grounding : The Grounds for EMC Design19 Path of Least Impedance Principle Which Path will the Return Current follow?

9 2112 VsIZZ Z= +1212 VsIZZ Z= +1221111111111111If Z >>Z I >>I (Ohm's Law)min{ }min{ }If Z, min{Z }min{R +jX }If R << Xmin{Z }min{ X }IZR jX = + The Second law of Thermodynamics: In a system, a process that occurs will tend to increase the total entropy of the : The Grounds for EMC Design20 Path of Least Impedance PrincipleWhich Path will the Return Current follow? At LOWFREQUENCIES, the current will follow the path of LEASTRESISTANCE, via ground (IG)1 /SS SjI IR L j = +0| |@ | |@ SSSSSSSZ RR jZ R j MZ LL RL = + = >> >> MSourceCableLoadRSLSRLIgI1 ISGrounding.

10 The Grounds for EMC Design21 At HIGH FREQUENCIES, the current will follow the path ofLEAST INDUCTANCE, via the return conductor (IS)| |@| |@ SSSSSSSZ RR jZ LLMRLZ R j >> >> = + = Path of Least Impedance PrincipleWhich Path will the Return Current follow?1 /SS SjI IR L j = + grounding : The Grounds for EMC Design22 Path of Least Impedance Principle Experiment Set-UpGrounding: The Grounds for EMC Design23 Path of Least Impedance PrincipleWhen is Inductance Minimized? Where is Inductance minimized?