46 DESIGN007 MAGAZINE I FEBRUARY 2020
Planar capacitance can reduce EMI by mini-
mizing the loop area, power supply ripple, and
plane resonance. It is also up to three times
better at heat transfer compared to a standard
core. System price performance can also be
improved by reducing the discrete capacitor
count and the size of the PCB and by improv-
ing signal and power integrity. The best feature
is that it is truly a drop-in replacement for stan-
dard core materials. If you need a quick fix for
the PDN, look no further!
Key Points
• In the time domain, decoupling capacitors
store and supply charge on demand to
the loads
• In the frequency domain, decoupling
capacitors also lower the impedance at
different frequencies to help meet the
AC impedance target
• Inductance pushes the AC impedance up
and shifts the resonant frequency of
capacitors down
• High-current simultaneous switching noise
from the power supply can interfere with
the signal return currents
• As core voltages drop, noise margins
become tighter
• The voltage, emanating from the vicinity
of the signal via, injects a propagating
wave into the cavity, which can excite the
cavity resonances or any other parallel
structure
• This cavity noise propagates as standing
waves spreading across the entire plane
pair
• If the plane cavity is not dampened, then
electromagnetic fields can radiate from
the board
• When optimized, the PDN can mitigate
many potential EMI issues and help
prevent EMC certification test failures
• Planar capacitor laminate or ECM is
becoming a cost-effective solution for
improved power integrity
• ECM takes the place of conventional
discrete decoupling capacitors over 1 GHz
• These ultra-thin laminates replace the
conventional power and ground planes
and should be positioned in the stackup
close to IC
• ECMs can have a capacitance density of
up to 20 nF per square inch and extremely
low inductance DESIGN007
Further Reading
B. Olney, "Beyond Design: Plane Crazy, Part 1," The PCB De-
sign Magazine, December 2015.
B. Olney, "Beyond Design: Plane Crazy, Part 2," The PCB
Design Magazine, January 2015.
B. Olney, "Beyond Design: PDN Planning and Capacitor Se-
lection, Part 1," The PCB Design Magazine, December 2013.
B. Olney, "Beyond Design: PDN Planning and Capacitor Se-
lection, Part 2," The PCB Design Magazine, January 2014.
B. Olney, "Beyond Design: Decoupling Capacitor Place-
ment," The PCB Design Magazine, January 2016.
B. Olney, "Beyond Design: Plane Cavity Resonance," The
PCB Design Magazine, September 2017.
B. Olney, "Beyond Design: Ground Bounce," Design007
Magazine, January 2018.
B. Olney, "Beyond Design: The 10 Fundamental Rules of
HSD, Part 3," Design007 Magazine, November 2018.
B. Olney, "Beyond Design: Materials Selection for SERDES
Design," The PCB Design Magazine, September 2013.
Oak-Mitsui Technologies, "Improved Power Delivery and
Reduce Noise with Embedded Capacitance."
I. Novak, Signal Integrity Journal.
E. Bogatin, Signal and Power Integrity: Simplified, Prentice
Hall, 2008.
Barry Olney is managing director
of In-Circuit Design Pty Ltd. (iCD),
Australia, a PCB design service
bureau that specializes in board-
level simulation. The company
developed the iCD Design Integ-
rity software incorporating the iCD
Stackup, PDN, and CPW Planner. The software can be
downloaded at icd.com.au. To read past columns or
contact Olney, click here.
