FEBRUARY 2018 I DESIGN007 MAGAZINE 51
• The best way to avoid EMI radiation
from PDNs is to ensure a resonance-free
impedance profile.
• BGA power/ground vias go directly to
the plane and so should the decap
power/ground vias, which reduce loop
inductance by ~30%.
• Decaps should be placed around the
perimeter of the IC on the same side of the
board and routed directly to the planes.
• The effective impedance of the PDN
should be kept below the target impedance
up to the maximum required bandwidth.
• Target impedance is the most crucial
metric when evaluating PDN performance.
• The circuit designer can combine the
target impedances for several chips on the
same PCB power rail by adding linearly
at DC and low frequencies and statistically
at higher frequencies.
• As frequency goes up, peak currents
become spatially isolated.
References
1. Beyond Design: PDN: Decoupling Capaci-
tor Placement, Power Distribution Network
Planning, Learning the Curve.
2. SI List forum: Steve Weir, Larry Smith.
3. Comparison of PDN Design Methods, Ist-
van Novak, DesignCon 2006.
4. Principles of Power Integrity for PDN
Design, Larry Smith and Eric Bogatin.
5. High-Speed Digital Design, Howard Johnson.
6. Target image: Modified from Melanie
Boylan, Stomp Social Media Training.
Barry Olney is managing director of
In-Circuit Design Pty Ltd (iCD), Aus-
tralia, a PCB design service bureau
that specializes in board-level
simulation. The company developed
the iCD Design Integrity software
incorporating the iCD Stackup, PDN and CPW Planner.
The software can be downloaded from www.icd.com.au.
To contact Olney, or read past columns, click here.
Manipulating Light with
Nanoscale Objects
Scientists at The University of New Mexico study-
ing the field of nanophotonics are developing new per-
spectives never seen before through their research.
In turn, the understanding of these theoretical con-
cepts is enabling physical scientists to create more
efficient nanostructures.
The research, says Assistant Professor Alejan-
dro Manjavacas, in the Department of Physics and
Astronomy at The University of New Mexico in a
paper titled "Hybridization of Lattice Resonances,"
investigates how periodic arrays of nanospheres or
atoms interact with light. These systems are made by
repeating a unit cell periodically, much like a chess-
board is made by repeating two differently colored
squares in a pattern.
As part of the research, Manjavacas and his team
composed by Sebastian Baur, a visiting graduate stu-
dent from Germany, and Stephen Sanders, a graduate
student in Physics and Astronomy, investigated the
optical properties of periodic arrays of plasmonic
nanoparticles with multi-particle unit cells. Specifi-
cally, they sought to understand how the geometry of
complex arrangements of plasmonic nanostructures
can be harnessed to control their optical responses.
Manjavacas and his team also explored systems
with three- and four-particle unit cells, like a chess-
board with three or four different kinds of colored
squares, and showed that they can be designed to
support resonances with complex response patterns
in which different groups of particles in the unit cell
can be selectively excited.
