April 2015 • The PCB Design Magazine 61
Important Points to Remember
• The dynamic characteristics of the cur-
rent sink or load determine the effective area
in which the capacitance of the PCB can be uti-
lized.
• In the case where the PCB is much larger
than the calculated effective area, high dielectric
materials are of minimal impact in noise volt-
age suppression. Better performance is achieved
by increasing capacitance either by minimizing
power plane spacing, or by increasing the num-
ber of plane pairs attached to the current sink.
• In the case where the PCB is larger than
the calculated effective area, further increases in
plane area outside of the effective radius/area
also have minimal impact on performance.
• In the case where the PCB is smaller than
the calculated effective area; increasing the ca-
pacitance by using higher dielectric constant
materials can improve noise voltage perfor-
mance. However, similar, if not better results
are achieved by decreasing the spacing or add-
ing additional plane pairs.
• Decreasing the plane pair spacing not only
increases the capacitance but also decreases the
inductance of the structure.
• The PCB is only one part of a PDN. The
VRM, discrete decoupling capacitors, chip pack-
age, and on-die capacitance are also very im-
portant in achieving the desired performance.
PCBDESIGN
References
1. Right the First Time, A Practical Hand-
book on High-Speed PCB and System Design,
Volume 2, by Lee W. Ritchey.
2. Electromagnetic Compatibility Engineer-
ing, by Henry W. Ott.
3. Signal Integrity: Simplified, by Eric Boga-
tin.
article
EFFECTIvE DECoUPLING RADIUS continues
Figure 9: showing the results of experiment 6
when adjusting the dielectric constant higher.
The peak noise voltage has decreased near the
corners to 66mv, but only to 93.2mv at the
current sink.
Kirk Fabbri is owner of KsPT
engineering Consulting llC
and electrical engineer for
l-3 Communications—Avionics
systems. he can be reached at
kirk.fabbri@l-3com.com.
The most recent Mercedes automatic car looks
just like a car on the outside but like a lounge
from the inside. The car, based on the concept
F 015 "luxury in Motion" showcased at the Consumer
electronics show, is totally self-driving but has a brake
and steering wheel if one wants to drive it manually.
Tesla, Audi, Google and a number of other com-
panies are trying to create their own adaptations of
driverless cars, satisfying the predictions that they
will be a reality on the roads possibly by the end of
this decade.
in fact, all the technology required for a self-
driving car is already present. existing features such
as self-parking preview and adaptive cruise control
show what a fully automatic car can do.
Driverless Cars to Renovate
Automotive Industry
