EM Noise Mitigation in Electronic Circuit Boards and Enclosures Omar M. Ramahi, Lin Li, Xin Wu, Vijaya Chebolu, Vinay Subramanian, Telesphor Kamgaing, Tom Antonsen, Ed Ott, and Steve Anlage A. James Clark School of Engineering University of Maryland, College Park Microwave Effects & Chaos in 21st Century Analog & Digital Electronics AFOSR MURI June 2002 Review MURI contract F496200110374
Primary Objectives Make each of the following less susceptible to EM noise, or alternatively, more quiet Chasses Packages Printed circuit boards
Outline Quiet Chasses a) Developing 3-Dimensional Full-Wave Predictive Tools for Cavity Resonance and S Parameter Computation and Extraction b) Using lossy material coating to reduce aperture radiation c) Using meta-material (high-impedance surface) to reduce emissions from apertures. Quiet Printed Circuit Boards a) Developing fast predictive modeling tools b) Reducing noise in printed circuit boards using highimpedance surface.
Our Philosophy Concept Development Numerical validation and prototyping Experimental verification
Apertures are Everywhere!! Highest Vulnerability Shielding wall with opening for audio speaker Opening for air ventilation Opening for mounting display Shielding chassis with aesthetics design
EM Interference Entry Points and Noise Channels Chassis contains: Apertures entry point of radiation Cables entry point for conducted radiation Printed circuit boards (PCB) constitute noise channels. If not quiet can be a source of interference and radiation 4. Packages constitute noise channels
S Parameter Calculation and Extraction Resonance Prediction
Finite-Difference Time-Domain Model Treat enclosure as a two-port network Absorbing Boundary Port 1 Port 2
FDTD Simulation Results
Minimizing Radiation from Apertures
Classical EM Aperture Research Developing techniques to predict aperture radiation Multi-aperture coupling Our emphasis: Understand physical distribution of current in the close proximity of Apertures and its effect on near- and far-field radiation
Transmission Line Interpretation of Aperture outgoing outgoing termination Current source termination incoming incoming
Lossy Material Coating Metallic shield Lossy coating Aperture
FDTD Modeling
Alternative techniques Electric Field (db) No lossy material Lossy pads Lossy edge Frequency Lossy edge Lossy pads
Electromagnetic Band Gap Structures Single Cell
HFSS Simulation Preliminary Results Without HIS With HIS
On-going Research in Aperture Radiation Effect of conductivity on near and far field Effect of resistive film are on fields Effect of resistive film on coupling between adjacent apertures
Silencing Printed Circuit Boards
Noisy Circuit Boards A source of internal interference and external radiation this active device experiences a disturbance in its power supply voltages due to via A External radiation via A via C V HIGH via A is part of a signal trace connecting the switching device via B field propagation caused by transient on via A V LOW via C is part of a signal trace and it experiences radial propagating noise due to via A
FDFD 2-D Model 2 2 [ + k ] Ez ( r) = δ ( r r0 ) Source located at r o FDFD grid 2 2 [ + k ] E ( r ) z z = hez Z A c Top view Voltage-controlled Current source Representing lumped element ε r h Computational domain h = planes separation, K = wave number, Z c = impedance of load Side view
Numerical Validation and Results Case 1: 30.5cm x 25cm Board with 99 Capacitors 0-10 -20-30 S12 (db) -40-50 -60-70 -80-90 no caps 99 caps 0 200 400 600 800 1000 Frequency (MHz) Decoupling Capacitors C=10nF, L=2nH S12 (db) 0-20 -40-60 -80-100 -120-140 Expt FDFD 0 200 400 600 800 1000 Frequency (MHz)
E field distribution across the board Effect of Capacitors Placement at 200MHz and 1GHz Effective No caps 200 MHz 99 caps 200 MHz NOT Effective no caps 1 GHz 99 caps 1 GHz
Numerical Validation and Results Capacitors wall 0-10 Feed port -20 Receive port (2.5cm, 2.5cm) (12.5cm, 15cm) S12 (db) -30-40 -50-60 -70-80 -90 No Caps 99 Caps 2"x2" wall of caps 0 200 400 600 800 1000 Frequency (MHz) Receive port Capacitors wall (2.5cm, 2.5cm) Feed port (12.5cm, 15cm) S12 (db) 0-10 -20-30 -40-50 -60-70 -80-90 -100-110 -120-130 -140 no caps 99 caps boundary wall of caps 0 200 400 600 800 1000 Frequency (MHz)
Numerical Validation and Results 2cm x 2cm Package with and without RC pairs RC element 180 160 140 120 No RC pairs 4 RC pairs 5 mm Source Z11 (Ohm) 100 80 60 40 5 mm RC element: R=0.6 Ω, C=50 pf 20 0 0 2 4 6 8 10 Frequency (GHz)
Novel Material: Do they have any thing to offer in Noise Reduction? Meta-material Negative Permittivity material High Impedance Ground Planes Photonic Band Gap material Textured Surface
High Impedance Surface As a Series of Parallel LC Resonators C = W ( ε1 + ε 2 ) Cosh π 1 a g L depends primarily on the length of the via Z 0 = µ ε ω Z BW = = ω 0 0 0 Z 0 Z = L C ω 0 = increasing either L or C can decrease the center frequency. But increasing L will also help increase the relative bandwidth. The constraint on the board thickness is therefore one of the fundamental limit on achievable low frequencies. 1 LC
A Novel Power Plane with Integrated Simultaneous Switching Noise Mitigation Capability using High Impedance Surface Top metal plate a patch Bottom metal planet g via
Increasing Band Gap by increasing inductance without affecting board thickness or periodicity lower via upper via Surface patches top plate a bottom plate a g half-loop inductor normal to the vias upper via lower via Increasing inductance while maintaining constant periodicity
Numerical Simulation Results using HFSS Achieved a 3.2 GHz 20 db bandwidth!
Summary 1. Developed S-parameter extraction methodology for Finite-Difference Time-Domain Simulation of resonant structures 2. Developed a technique for reducing aperture radiation by using external conductive coating 3. Developed fast numerical algorithm for switching noise simulation in printed circuit boards 4. Developed two new concepts for noise mitigation in circuit boards and from apertures using high impedance surfaces (photonic band gap material)